The Laser Interferometer Space Antenna (LISA) is a partnership between the European Space Agency (ESA) and NASA to build a Gravitational Wave (GW) observatory. The observatory, which consists of a three-spacecraft constellation with a nominal separation of 2.5 million km between each spacecraft, provides a tool for scientists to directly detect gravitational waves generated from various astronomical phenomena in a waveband that is not accessible from Earth. NASA is developing laser transmitters as one of the potential US contributions to LISA. The NASA laser design leverages lessons learned from previous flight missions and included the latest technologies in photonics packaging and reliability engineering to ensure a laser lifetime of <16 years covering integration and test through a possible extended mission phase. As part of the laser development process, NASA’s Goddard Space Flight Center (GSFC) requested support from the NASA Engineering and Safety Center (NESC) to independently assess the Technology Readiness Level (TRL) of the LISA Laser System (LS). The independent assessment included the following tasks: (a) assess the design for weaknesses and suggest improvements to mitigate risks, (b) assess the laser reliability plan for weaknesses and suggest improvements to mitigate risks and improve effectiveness, and (c) assess the current redundancy plan on laser subsystems for weaknesses and suggest improvements to mitigate risks and improve effectiveness. The NESC team comprised of a team of subject matter experts (SMEs) and performed a 12-month review of every aspect of the laser design. We present the assessment findings and the current development progress of the LISA laser to meet the mission requirements with a delivery of a form, fit, and functional TRL6 laser to the LSIA mission by late 2023
KEYWORDS: Laser energy, Calibration, Signal to noise ratio, LIDAR, Sensors, Analog electronics, Pulsed laser operation, Absorption, Carbon monoxide, Signal detection
Integrated path differential absorption (IPDA) lidar is an active remote sensing technique for monitoring different atmospheric species. The technique relies on wavelength differentiation between strong and weak absorbing features normalized to the transmitted energy. An advanced 2-μm triple-pulse IPDA lidar was developed at NASA Langley Research Center for active sensing of carbon dioxide and water vapor simultaneously. The IPDA transmitter produces three successive laser pulses separated by a short interval (200 μs) with a repetition rate of 50Hz. Measurement of laser pulse energy accurately is a prerequisite for the retrieval of gas mixing ratios from IPDA. Due to the short interval between the three transmitted pulses, conventional thermal energy monitors underestimate the total transmitted energy. The design and calibration of a 2-μm triple-pulse laser energy monitor are presented. The design is based on a high speed, extended range InGaAs pin quantum detector suitable for separating the three pulse events. Pulse integration is applied for converting the detected pulse power into energy. The results obtained from the laser energy monitor were compared to an ultra-fast energy-meter reference for energy scaling and verification. High correlations between the pin energy monitor and the total transmitted energy were obtained. The objective of this development is to reduce measurement biases and errors using the triple-pulse IPDA technique.
Atmospheric water vapor and carbon dioxide are important greenhouse gases that significantly contribute to the global radiation budget on Earth. A 2-micron triple-pulse, Integrated Path Differential Absorption (IPDA) lidar instrument for ground and airborne atmospheric carbon dioxide and water vapor concentration measurements using direct detection was developed at NASA Langley Research Center. This active remote sensing instrument provides an alternate approach with significant advantages for measuring atmospheric concentrations of the gases. A high energy pulsed laser transmitter approach coupled with sensitive receiver detection provides a high-precision measurement capability by having a high signal-to-noise ratio. This paper presents the concept, development, integration and testing of the 2-micron triple-pulse IPDA. The integration includes the various IPDA transmitter, receiver and data acquisition subsystems and components. Ground and airborne testing indicated successful operation of the IPDA lidar.
A 2-micron pulsed, Integrated Path Differential Absorption (IPDA) lidar instrument for ground and airborne atmospheric CO2 concentration measurements via direct detection method is being developed at NASA Langley Research Center. This instrument will provide an alternate approach to measure atmospheric CO2 concentrations with significant advantages. A high energy pulsed approach provides high precision measurement capability by having high signal-to-noise level and unambiguously eliminates the contamination from aerosols and clouds that can bias the IPDA measurement.
Carbon dioxide (CO2) is an important greenhouse gas that significantly contributes to the carbon cycle and global radiation budget on Earth. CO2 role on Earth’s climate is rather complicated due to different interactions with various climate components that include the atmosphere, the biosphere and the hydrosphere.
The 2-micron wavelength region is suitable for atmospheric carbon dioxide (CO2) measurements due to the existence of distinct absorption features for the gas at this wavelength region [1]. For more than 20 years, researchers at NASA Langley Research Center (LaRC) have developed several high-energy and high repetition rate 2-micron pulsed lasers [2]. Currently, LaRC team is engaged in designing, developing and demonstrating a triple-pulsed 2-micron direct detection Integrated Path Differential Absorption (IPDA) lidar to measure the weighted-average column dry-air mixing ratios of carbon dioxide (XCO2) and water vapor (XH2O) from an airborne platform [1, 3-5]. This novel technique allows measurement of the two most dominant greenhouse gases, simultaneously and independently, using a single instrument. This paper will provide status and details of the development of this airborne 2-micron triple-pulse IPDA lidar. The presented work will focus on the advancement of critical IPDA lidar components. Updates on the state-of-the-art triple-pulse laser transmitter will be presented including the status of seed laser locking, wavelength control, receiver and detector upgrades, laser packaging and lidar integration. Future plans for IPDA lidar ground integration, testing and flight validation will also be discussed. This work enables new Earth observation measurements, while reducing risk, cost, size, volume, mass and development time of required instruments.
An airborne 2-μm triple-pulse integrated path differential absorption (IPDA) lidar is currently under development at NASA Langley Research Center (LaRC). This lidar targets both atmospheric carbon dioxide (CO2) and water vapor (H2O) column measurements, simultaneously. Advancements in the development of this IPDA lidar are presented in this paper. Updates on advanced two-micron triple-pulse high-energy laser transmitter will be given including packaging and lidar integration status. In addition, receiver development updates will also be presented. This includes a state-of-the-art detection system integrated at NASA Goddard Space Flight Center. This detection system is based on a newly developed HgCdTe (MCT) electron-initiated avalanche photodiode (e-APD) array. Future plan for IPDA lidar system for ground integration, testing and flight validation will be discussed.
An airborne 2-micron double-pulsed Integrated Path Differential Absorption (IPDA) lidar has been developed for atmospheric CO2 measurements. This instrument has been flown in spring of 2014 for a total of ten flights with 27 flight hours. The results of these test flights clearly show the capability of the lidar instrument to measure the total column amount of atmospheric CO2 from aircraft to the ground or cloud top.
The 2-micron wavelength region is suitable for atmospheric carbon dioxide (CO2) measurements due to the existence of distinct absorption feathers for the gas at this particular wavelength. For more than 20 years, researchers at NASA Langley Research Center (LaRC) have developed several high-energy and high repetition rate 2-micron pulsed lasers. This paper will provide status and details of an airborne 2-micron triple-pulse integrated path differential absorption (IPDA) lidar. The development of this active optical remote sensing IPDA instrument is targeted for measuring both CO2 and water vapor (H2O) in the atmosphere from an airborne platform. This presentation will focus on the advancement of the 2-micron triple-pulse IPDA lidar development. Updates on the state-of-the-art triple-pulse laser transmitter will be presented including the status of seed laser locking, wavelength control, receiver telescope, detection system and data acquisition. Future plans for the IPDA lidar system for ground integration, testing and flight validation will also be presented.
An airborne 2-m triple-pulse integrated path differential absorption (IPDA) lidar is currently under development at
NASA Langley Research Center (LaRC). This IPDA lidar system targets both atmospheric carbon dioxide (CO2) and
water vapor (H2O) column measurements. Independent wavelength control of each of the transmitted laser pulses is a
key feature for the success of this instrument. The wavelength control unit provides switching, tuning and locking for
each pulse in reference to a 2-μm CW laser source locked to CO2 line-center. Targeting the CO2 R30 line center, at
2050.967 nm, a wavelength locking unit has been integrated using semiconductor laser diode. The CO2 center-line
locking unit includes a laser diode current driver, temperature controller, center-line locking controller and CO2
absorption cell. This paper presents the CO2 center-line locking unit architecture, characterization procedure and results.
Assessment of wavelength jitter on the IPDA measurement error will also be addressed by comparison to the system
design.
For more than 15 years, NASA Langley Research Center (LaRC) has contributed in developing several 2-micron carbon dioxide active remote sensors using the DIAL technique. Currently, an airborne 2-micron triple-pulse integrated path differential absorption (IPDA) lidar is under development at NASA LaRC. This paper focuses on the advancement of the 2-micron triple-pulse IPDA lidar development. Updates on the state-of-the-art triple-pulse laser transmitter will be presented including the status of wavelength control, packaging and lidar integration. In addition, receiver development updates will also be presented, including telescope integration, detection systems and data acquisition electronics. Future plan for IPDA lidar system for ground integration, testing and flight validation will be presented.
A double-pulsed, 2-μm Integrated Path Differential Absorption (IPDA) lidar instrument for atmospheric carbon dioxide (CO2) measurements is successfully developed at NASA Langley Research Center (LaRC). Based on direct detection technique, the instrument can be operated on ground or onboard a small aircraft. Key features of this compact, rugged and reliable IPDA lidar includes high transmitted laser energy, wavelength tuning, switching and locking, and sensitive detection. As a proof of concept, the IPDA ground and airborne CO2 measurement and validation will be presented. Ground validation of the IPDA lidar column CO2 measurements were conducted at NASA LaRC using hard targets and a calibrated in situ sensor. Airborne validation, conducted onboard the NASA B-200 aircraft, included CO2 plume detection from power stations incinerators, in-flight CO2in situ sensor and air sampling at different altitude, conducted by NOAA at the same site. Airborne measurements, spanning for 20 hours, were obtained from different targets such as soil, vegetation, sand, snow and ocean. In addition, cloud slicing was examined over the ocean. These flight validations were conducted at different altitudes, up to 6 km, with different wavelength controlled weighing functions. CO2 measurement results agree with modeling results from different sensors.
Carbon dioxide (CO2) is an important greenhouse gas that significantly contributes to the carbon cycle and global radiation budget on Earth. CO2 role on Earth’s climate is complicated due to different interactions with various climate components that include the atmosphere, the biosphere and the hydrosphere. Although extensive worldwide efforts for monitoring atmospheric CO2 through various techniques, including in-situ and passive sensors, are taking place high uncertainties exist in quantifying CO2 sources and sinks. These uncertainties are mainly due to insufficient spatial and temporal mapping of the gas. Therefore it is required to have more rapid and accurate CO2 monitoring with higher uniform coverage and higher resolution. CO2 DIAL operating in the 2-μm band offer better near-surface CO2 measurement sensitivity due to the intrinsically stronger absorption lines. For more than 15 years, NASA Langley Research Center (LaRC) contributed in developing several 2-μm CO2 DIAL systems and technologies. This paper focuses on the current development of the airborne double-pulsed and triple-pulsed 2-μm CO2 integrated path differential absorption (IPDA) lidar system at NASA LaRC. This includes the IPDA system development and integration. Results from ground and airborne CO2 IPDA testing will be presented. The potential of scaling such technology to a space mission will be addressed.
Double-pulse 2-micron lasers have been demonstrated with energy as high as 600 mJ and up to 10 Hz repetition rate.
The two laser pulses are separated by 200 µs and can be tuned and locked separately. Applying double-pulse laser in
DIAL system enhances the CO2 measurement capability by increasing the overlap of the sampled volume between the
on-line and off-line. To avoid detection complicity, integrated path differential absorption (IPDA) lidar provides higher
signal-to-noise ratio measurement compared to conventional range-resolved DIAL. Rather than weak atmospheric
scattering returns, IPDA rely on the much stronger hard target returns that is best suited for airborne platforms. In
addition, the IPDA technique measures the total integrated column content from the instrument to the hard target but
with weighting that can be tuned by the transmitter. Therefore, the transmitter could be tuned to weight the column
measurement to the surface for optimum CO2 interaction studies or up to the free troposphere for optimum transport
studies. Currently, NASA LaRC is developing and integrating a double-Pulsed 2-µm direct detection IPDA lidar for CO2
column measurement from an airborne platform. The presentation will describe the development of the 2-μm IPDA lidar
system and present the airborne measurement of column CO2 and will compare to in-situ measurement for various
ground target of different reflectivity.
Knowledge derived from global tropospheric wind measurement is an important constituent of our overall understanding of climate behavior [1]. Accurate weather prediction saves lives and protects properties from destructions. High-energy 2-micron laser is the transmitter of choice for coherent Doppler wind detection. In addition to the eye-safety, the wavelength of the transmitter suitably matches the aerosol size in the lower troposphere. Although the technology of the 2-micron laser has been maturing steadily, lidar derived wind data is still a void in the global weather database. In the last decade, researchers at NASA Langley Research Center (LaRC) have been engaged in this endeavor, contributing to the scientific database of 2-micron lidar transmitters. As part of this effort, an in depth analysis of the physics involved in the workings of the Ho: Tm laser systems have been published. In the last few years, we have demonstrated lidar transmitter with over1Joule output energy. In addition, a large body of work has been done in characterizing new laser materials and unique crystal configurations to enhance the efficiency and output energy of the 2-micron laser systems. At present 2-micron lidar systems are measuring wind from both ground and airborne platforms. This paper will provide an overview of the advancements made in recent years and the technology maturity levels attained.
Integrated path differential absorption (IPDA) lidar is a remote sensing technique for monitoring different atmospheric species. The technique relies on wavelength differentiation between strong and weak absorbing features normalized to the transmitted energy. 2-μm double-pulsed IPDA lidar is best suited for atmospheric carbon dioxide measurements. In such case, the transmitter produces two successive laser pulses separated by short interval (200 μs), with low repetition rate (10Hz). Conventional laser energy monitors, based on thermal detectors, are suitable for low repetition rate single pulse lasers. Due to the short pulse interval in double-pulsed lasers, thermal energy monitors underestimate the total transmitted energy. This leads to measurement biases and errors in double-pulsed IPDA technique. The design and calibration of a 2-μm double-pulse laser energy monitor is presented. The design is based on a highspeed, extended range InGaAs pin quantum detectors suitable for separating the two pulse events. Pulse integration is applied for converting the detected pulse power into energy. Results are compared to a photo-electro-magnetic (PEM) detector for impulse response verification. Calibration included comparing the three detection technologies in singlepulsed mode, then comparing the pin and PEM detectors in double-pulsed mode. Energy monitor linearity will be addressed.
We demonstrated upconversion assisted detection of a 2.05-μm signal by sum frequency generation to generate a 700-nm light using a bulk periodically poled lithium niobate crystal. The achieved 94% intrinsic upconversion efficiency and 22.58% overall detection efficiency at a pW level of 2.05 μm pave the path to detect extremely weak infrared (IR) signals for remote sensing applications.
Compact, reliable and conductively-cooled solid state 2-micron laser technology is a critical component of the 3-D Winds mission envisioned in the NRC Decadal survey. In order to mature the 2-micron laser technology to a Technical Readiness Level of 5 (TRL-5), we are developing a conductively-cooled single-frequency 2-micron laser meeting the performance requirements for this wind LIDAR mission and able to operate in vacuum. Conductive cooling is accomplished via heat pipes attached to a reconfigurable condenser plate. The ruggedized mechanical design is based upon design concepts used and validated for the NASA Ice, Cloud and Land Elevation Satellite-2 (ICESat-2) Mission. Achieving TRL-5 has particular challenges for this technology due to its unique requirements. The cold operating temperature mandated by the laser crystal (Ho:Tm:LuLF) and the long resonator required to generate <100 ns pulsewidths needed to maximize the LIDAR resolution, make stabilizing the laser more difficult than many other lasers. The completion and demonstration of this laser provides a platform for further maturation of solid state 2 micron laser technology to the TRL-6 required for space-based deployment.
Atmospheric carbon dioxide (CO2) is an important greenhouse gas that significantly contributes to the carbon cycle and global radiation budget on Earth. Active remote sensing of CO2 is important to address several limitations that contend with passive sensors. A 2-micron double-pulsed, Integrated Path Differential Absorption (IPDA) lidar instrument for ground and airborne atmospheric CO2 concentration measurements via direct detection method is being developed at NASA Langley Research Center. This active remote sensing instrument will provide an alternate approach of measuring atmospheric CO2 concentrations with significant advantages. A high energy pulsed approach provides high-precision measurement capability by having high signal-to-noise ratio level and unambiguously eliminates the contamination from aerosols and clouds that can bias the IPDA measurement. Commercial, on the shelf, components are implemented for the detection system. Instrument integration will be presented in this paper as well as a background for CO2 measurement at NASA Langley research Center.
A field demonstration was done from Virginia Beach, Virginia, to show the use of high-energy (250-mJ) eyesafe Doppler lidar for measurements of offshore wind. The lidar is located onshore and pointed near-horizontally to reach a target area many kilometers away. In sample measurements, the lidar scan's hypothetical turbine is located 6 km away. For one beam elevation of interest, the horizontal wind vector is measured by scanning the beam in azimuth. The elevation can then be changed to profile the wind at many altitudes. An example measurement is shown in which wind vector is determined at six altitudes covering the height of a supposed turbine and above. In addition to the wind vector, wind shear is measured across a turbine blade span width. Over a two-week period in October 2011, range capability was found to vary from 4.5 to 17 km depending on weather and aerosol backscatter conditions. A comparison was made with an anemometer to validate the lidar's measurements.
Sustained research efforts at NASA Langley Research Center (LaRC) during last fifteen years have resulted in a
significant advancement in 2-micron diode-pumped, solid-state laser transmitter for wind and carbon dioxide
measurement from ground, air and space-borne platform. Solid-state 2-micron laser is a key subsystem for a
coherent Doppler lidar that measures the horizontal and vertical wind velocities with high precision and resolution.
The same laser, after a few modifications, can also be used in a Differential Absorption Lidar (DIAL) system for
measuring atmospheric CO2 concentration profiles. Researchers at NASA Langley Research Center have
developed a compact, flight capable, high energy, injection seeded, 2-micron laser transmitter for ground and
airborne wind and carbon dioxide measurements. It is capable of producing 250 mJ at 10 Hz by an oscillator and
one amplifier. This compact laser transmitter was integrated into a mobile trailer based coherent Doppler wind and
CO2 DIAL system and was deployed during field measurement campaigns. This paper will give an overview of 2-
micron solid-state laser technology development and discuss results from recent ground-based field measurements.
A pulsed, 2-μm coherent Differential Absorption Lidar (DIAL) / Integrated Path Differential Absorption (IPDA)
transceiver, developed under the Laser Risk Reduction Program (LRRP) at NASA, is integrated into a fully functional
lidar instrument. This instrument measures atmospheric CO2 profiles (by DIAL) from a ground platform. It allows the
investigators to pursue subsequent in science-driven deployments, and provides a unique tool for Active Sensing of CO2
Emissions over Night, Days, and Seasons (ASCENDS) validation that was strongly advocated in the recent ASCENDS
Workshop.
A 2-µm wavelength coherent Doppler lidar for wind measurement has been developed of an unprecedented laser pulse energy of 250-mJ in a rugged package. This high pulse energy is produced by a Ho:Tm:LuLiF laser with an optical amplifier. While the lidar is meant for use as an airborne instrument, ground-based tests were carried out to characterize performance of the lidar. Atmospheric measurements are presented, showing the lidar's capability for wind measurement in the atmospheric boundary layer and free troposphere. Lidar wind measurements are compared to a balloon sonde, showing good agreement between the two sensors.
In the process of designing a coherent, high energy 2μm, Doppler wind Lidar, various types of Q-Switch materials and
configurations have been investigated for the oscillator. Designing an oscillator with a relatively low gain laser material
presents challenges related to the management high internal circulating fluence due to high reflective output coupler.
This problem is compounded by the loss of hold-off. In addition, the selection has to take into account the round trip
optical loss in the resonator and the loss of hold-off. For this application, a Brewster cut 5mm aperture, fused silica AO
Q-switch is selected. Once the Q-switch is selected various rf frequencies were evaluated. Since the Lidar has to perform
in single longitudinal and transverse mode with transform limited line width, in this paper, various seeding
configurations are presented in the context of Q-Switch diffraction efficiency. The master oscillator power amplifier has
demonstrated over 350mJ output when the amplifier is operated in double pass mode and higher than 250mJ when
operated in single pass configuration. The repetition rate of the system is 10Hz and with a pulse length of 200ns.
A coherent Doppler lidar at 2 µm wavelength has been built with higher output energy (100 mJ) than previously available. The laser transmitter is based on diode-pumped Ho:Tm:LuLiF, a recently developed laser material that allows more efficient energy extraction. Single-frequency operation is achieved by a ramp-and-fire injection seeding technique. An advanced photodetector architecture is used incorporating photodiodes in a dual-balanced configuration. A digital signal processing system has been built, allowing real-time display of wind and aerosol backscatter data products. The high pulse energy and receiver efficiency provides for measurement of wind fields to ranges not seen before with 2 µm lidars, and example wind measurements were made to show this capability.
The design of a compact coherent laser radar transmitter for tropospheric wind sensing is presented. This
system is hardened for ground and airborne applications. As a transmitter for a coherent wind Lidar, this
laser has stringent spectral line width and beam quality requirements. Although the absolute wavelength is
not fixed, the output wavelength should avoid atmospheric CO2 and H2O absorption lines. The design
architecture includes a seed laser, a power oscillator and a single amplifier. The laser material used for this
application is a Ho:Tm:LuLF crystal. The 3-meter long folded ring resonator produces 100-mJ with a
temporal pulse length around 185 ns. A final output of 300 mJ at a repetition rate of 10 Hz is achieved by
using an amplifier in a double pass format. The operating temperature is set around 15°C for the pump
diode lasers and 5°C for the rod. Since the laser design has to meet high-energy as well as high beam
quality requirements, close attention is paid to the laser head design to avoid thermal distortion in the rod.
A side-pumped configuration is used and heat is removed uniformly by passing coolant through a tube
slightly larger than the rod to reduce thermal gradient. This paper also discusses issues related to beam
distortion due to high repetition rate. In addition, energy, seeding technique, and beam quality evaluation of
the engineering verification laser will be presented.
Significant advancements in the 2-micron laser development have been made recently. Solid-state 2-micron
laser is a key subsystem for a coherent Doppler lidar that measures the horizontal and vertical wind
velocities with high precision and resolution. The same laser, after a few modifications, can also be used in
a Diffrencial Absorption Lidar (DIAL) system for measuring atmospheric CO2 concentration profiles. The
world record 2-micron laser energy is demonstrated with an oscillator and two amplifiers system. It
generates more than one joule per pulse energy with excellent beam quality. Based on the successful
demonstration of a fully conductive cooled oscillator by using heat pipe technology, an improved fully
conductively cooled 2-micron amplifier was designed, manufactured and integrated. It virtually eliminates
the running coolant to increase the overall system efficiency and reliability. In addition to technology
development and demonstration, a compact and engineering hardened 2-micron laser is under development.
It is capable of producing 250 mJ at 10 Hz by an oscillator and one amplifier. This compact laser is
expected to be integrated to a lidar system and take field measurements. The recent achievements push
forward the readiness of such a laser system for space lidar applications. This paper will review the
developments of the state-of-the-art solid-state 2-micron laser.
For space-based lidar applications, conductively cooled lasers have been identified as a critical technology for high energy, 2-micron laser transmitter. Effective thermal management is a challenge for high-energy, 2-micon lasers. In this paper, the design of a totally conductively cooled, diode pumped, 2-micron laser amplifier is presented. Based on the successful testing of a conductively cooled oscillator, concepts for a laser amplifier were developed. The newly designed amplifier consists of a 40 mm long Ho:Tm: LuLF rod being pumped by 4 banks of 5-radially arranged diode lasers totaling 80W pump power. Optical and thermal studies for the amplifier head are presented and discussed. Currently, the design of the amplifier head is being integrated into a complete amplifier subsystem for a conductive cooled Master Oscillator Power Amplifier (MOPA) laser.
Remote sensing using mid-infrared wavelength has many applications in pollution surveillance and atmosphere studies. However, high gain, low noise detectors or single photon counters are not available in the mid-infrared wavelength range. One approach to obtain single-photon detection in mid-infrared wavelength is to convert the mid-infrared radiations into visible/near-infrared wavelengths where high efficiency and low dark current detectors are easily available. In this paper, the up-conversion of mid-infrared radiations based on the quasi-phase matching condition of periodically poled lithium niobate (PPLN) is investigated. The bandwidth and efficiency are the two essential parameters for the up-conversion process. The optimal pump wavelength λlasero and PPLN period Λ can be determined from conservations of energy and momentum. Once the λlasero and Λ are defined, the spectral bandwidth corresponding to the full width at half maximum of frequency up-conversion can be calculated. The spectral bandwidth of mid-infrared radiations can exceed 130 nm for a 25 mm PPLN crystal when the pump laser operates in the optimum wavelength. It is wide enough to cover both the on and off wavelengths of the species of interest in a Differential Absorption Lidar. The maximum up-conversion bandwidth usually corresponds to the longest PPLN period allowed by the quasi-phase matching condition. The conversion efficiency increases with the pump laser intensity. Both the external cavity pumping approach with cavity locking technique and the intra-cavity pumping approach can greatly increase the up-conversion efficiency.
State of the art 2-micron lasers and other lidar components under development by NASA are being demonstrated and validated in a mobile test bed Doppler wind lidar. A lidar intercomparison facility has been developed to ensure parallel alignment of up to 4 Doppler lidar systems while measuring wind. Investigations of the new components; their operation in a complete system; systematic and random errors; the hybrid (joint coherent and direct detection) approach to global wind measurement; and atmospheric wind behavior are planned. Future uses of the VALIDAR (VALIDation LIDAR) mobile lidar may include comparison with the data from an airborne Doppler wind lidar in preparation for validation by the airborne system of an earth orbiting Doppler wind lidar sensor.
Spaceborne coherent Doppler wind lidars and CO2 Differential Absorption Lidars (DIALs) at eye-safe 2-μm spectral range have been proposed for several years for accurate global wind and carbon-oxide concentration profiling measurement. These lidar systems require Joule level laser pulse energy from laser transmitter and high efficiency. In this paper, we report a diode-pumped Ho:Tm:LuLF Master-Oscillator-Power-Amplifier (MOPA) developed to demonstrate Joule level output pulse energy. The MOPA consists of one master oscillator and two power amplifiers. The master oscillator was Q-switched and can be operated at single pulse mode or double pulse mode respectively. The single pulse operation is used for a coherent Doppler wind lidar and the double pulse operation for a CO2 Differential Absorption Lidar (DIAL). The output pulse energy of the master oscillator is 115 mJ for the single pulse operation and 186 mJ for the double pulse operation. To extract more energy from the pumping pulses and increase the efficiency of the MOPA, the first amplifier was set at a double pass configuration. The second amplifier was set at a single pass configuration to avoid the damage problem of the Ho:Tm:LuLF laser rod. Total output pulse energy of 0.63 J with an optical efficiency of 4.1% for single pulse operation and 1.05 J with an optical efficiency of 6.9% for double pulse operation were demonstrated.
Space Lidar applications benefits from efficient conductive cooled laser transmitters. Effective thermal management is a key challenge for high-energy laser development. In this paper, the design and performance of a totally conductive cooled 2µm laser is presented. Three heat pipes capable of removing 150 watts of heat both from the pump diode lasers and the rod were used in the design. A 2.5 m long ring resonator with two 5-m radii of curvature mirrors set a 2.36mm diameter TEMoo mode radius in the cavity. Despite the thermal gradient that was created in the Ho:Tm: LuLF crystal due to the cooling method and geometry, almost diffraction limited beam and up to 107 mJ of Q-switched output with a pulse length of 135ns was obtained. Such a laser transmitter can be used as a wind Lidar. It is especially suitable as a CO2 DIAL since two Q-switched pulses can be acquired for a single pump pulse due to the long lifetime of the Ho: 5I7 and 5I8 transition and the operating wavelength is near rich CO2 absorption lines.
Pulsed lasers are useful for remote sensing of wind and greenhouse gases to better understand the atmosphere and its impact on weather patterns and the environment. It is not always practical to develop and optimize new laser systems empirically due to the time and expense associated with such endeavors. A practical option is to use a laser model to predict various performance parameters and compare these with the needs required for a particular remote sensing application. This approach can be very useful in determining the efficacy of potential laser systems, saving both time and money before proceeding with the actual construction of a laser device. As a pedagogical example, the modeling of diode pumped Tm:Ho:YLF and Tm:Ho:LuLF lasers are examined. Tm:Ho lasers operating around 2.0 μm have been used for wind measurements such as clear air turbulence and wake vortices. The model predictions for the laser systems examined here are compared to the actual laser performance, validating the usefulness of the modeling approach. While Tm:Ho fluoride lasers are used as a pedagogical example, the model is applicable to any lanthanide series pulsed laser system. This provides a useful tool for investigating potential laser systems that meet the requirements desired for a variety of remote sensing applications.
It has been realized that eye-safe 2-mm all-solid-state lasers are important laser sources for an accurate measurement of the CO2 concentration in the atmosphere. Served as laser transmitters, they can be integrated into ground-based, airborne-base, and spaceborne-based CO2 Differential Absorption Lidars (DIALs) to accomplish the measurement. In addition, the lasers are also ideal laser pumping sources for a ZnGeP2 (ZGP) Optical Parametric Oscillator (OPO) or an Optical Parametric Amplifier (OPA) to achieve tunable laser output in 3~5 mm. In this spectrum region, the other important greenhouse gases, water vapor (H2O), carbon monoxide (CO), and methane (CH4) in the atmosphere can be measured. In this paper, we report a diode-pumped, double-pulsed, Q-switched, eye-safe Ho:Tm:LuLF laser at 2.05 mm developed for ground-based and airborne-based CO2 Differential Absorption Lidars (DIALs). The technology can be easily transferred to a space-borne CO2 DIAL in the future. The total output pulse energy of the laser is 220 mJ and 204 mJ per pair of pulses at 2 Hz and at 10 Hz respectively. The related optical energy conversion efficiency is 6.7% and 5.9% respectively.
High-energy 2-micron lasers have been incorporated in a breadboard coherent Doppler lidar to test component technologies and explore applications for remote sensing of the atmosphere. Design of the lidar is presented including aspects in the laser transmitter, receiver, photodetector, and signal processing. Sample data is presented on wind profiling and CO2 concentration measurements.
A tunable continuous-wave (CW) intracavity pumped periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) has been developed where a diode-pumped ring-cavity Nd:YAG laser is used as the pumping source. The idler tunable range from 2.3 μm to 3.9 μm with linewidth less than 15 MHz has been demonstrated. The slop efficiency of the idler output versus the diode pump power is ~ 5.6%. The idler output power at 3.4 μm reaches 370 mW when the diode output power is 21.5 W. The PPLN OPO will be applied to seed ZnGeP2 OPO pumped by a Tm:Ho:YLF laser (λ=2.05 μm). The ZnGeP2 OPO can be tuned between 3-10.5 μm. Combined PPLN OPO and ZnGeP2 OPO, the tunable range covers the strong absorption lines of most atmospheric pollutants, and overlaps the mid-infrared atmospheric windows of 3.4-5 μm and 8-13 μm. The mid-infrared emission source is a potential lidar transmitter for remote sensing applications.
Accurate global atmospheric remote sensing such as wind and carbon-oxide concentration profiling requires a coherent Doppler lidar and a Differential Absorption Lidar (DIAL) in an eye-safe spectrum range, respectively. Both Doppler lidar and DIAL should have laser transmitters with high pulse energy and high efficiency. There is no doubt that a Tm:Ho:YLF or Tm:Ho:LuLF laser oscillator with multistage amplifiers are appropriate candidates for these transmitters, especially for space-borne lidar systems. To achieve a high efficient laser transmitter, a collinear double-pass Tm:Ho:YLF laser amplifier has been designed and experimentally tested with a Tm:Ho:YLF laser oscillator. When laser pulses at a reasonably high energy, said 50 mJ here, from a Q-switched Tm:Ho:YLF laser oscillator were directly sent into a single-pass Tm:Ho:YLF amplifier, a gain of 1.86 was obtained at a pump pulse energy of 5.82 J. With a collinear double-pass configuration, a gain of 2.24 was achieved at same pump pulse energy level including all losses of the necessary optical elements, such as a thin film polarizer, a half-wave plate, and a Faraday rotator. More than 95% pulse energy was extracted from the double-pass amplifier, compared to a single-pass amplifier.
Two-micron lasers can be used in a variety of remote sensing and medical applications. In recent years, such lasers have been used for remote sensing of wind and CO2 to expand our understanding of the global weather system. The detection of clear air turbulence and wake vortex from aircraft has been proven to enhance air travel safety. In this paper, we present the design and performance of a high-energy diode pumped solid-state 2-micron laser transmitter. There has been a large body of work on 2 μm laser crystals using Tm and Ho ions doped in YLF and YAG hosts, but the use of LuLiF4 as a host is relatively recent. Studies comparing Ho:LuLiF4 and Ho:YLF show that both crystals have similar emission cross-sections for both 2.05 μm and 2.06 μm transitions. Tm:Ho:LuLiF4 has proven to produce 15%-20% more energy than Tm:Ho:YLF. This is primarily attributed to the variation of the thermal population distribution in the Ho: 5I7 and 5I8 energy levels. The laser crystal used for this experiment is grown in the crystalline a-axis. The resonator is a bow tie ring configuration with 3-m length. One of the mirrors in the resonator has a 3.5m curvature, which sets up a 1.8 mm TEMoo mode radius. The output mirror reflectivity is 72% and it is the dominant source of the resonator loss. An acousto-optic Q-Switch with Brewster angle switches the Q of the oscillator and defines the polarization of the laser output. This laser has a potential to produce a multi joule energy and replace the traditionally used Ho: Tm: YLF crystal.
We report on a diode pumped Tm: YLF laser generating 1.9 micrometers output. Recently, research is being pursued to produce laser wavelength around 2 micrometers by separating the Ho and Tm ions in different laser hosts. Compared to co-doped laser hosts; a higher efficiency performance can be achieved by directly pumping the Holmium with a 1.9 micrometers Tm laser due to the elimination of energy sharing between Tm and Ho as well as deleterious upconversion effects in co-doped systems. A 300-mJ Tm:YLF laser at room temperature has been demonstrated. The laser design and laser performance is described. To our knowledge, this is the highest energy ever reported for this laser material.
Solid-state 2-?m laser has been receiving considerable interest because of its eye-safe property and efficient diode pump operation. It has potential for multiple lidar applications to detect water vapor, carbon dioxide and winds. In this paper, we describe a 2-?m double pulsed Ho:Tm:YLF laser and end-pumped amplifier system. A comprehensive theoretical model has been developed to aid the design and optimization of the laser performance. In a single Q-switched pulse operation, the residual energy stored in the Tm atoms will be wasted. However, in a double pulses operation mode, the residual energy stored in the Tm atoms will repopulate the Ho atoms that were depleted by the extraction ofthe first Q-switched pulse. Thus, the Tm sensitized Ho:YLF laser provides a unique advantage in applications that require double pulse operation, such as DIfferential Absorption Lidar (DIAL). A total output energy of 146 nil per pulse pair under Q-switch operation is achieved with as high as 4.8 % optical to optical efficiency. Compared to a single pulse laser, 70% higher laser efficiency is realized. To obtain high energy while maintaining the high beam quality, a master-oscillator-power-amplifier 2-tim system is designed. We developed an end-pumped Ho:Tm:YLF disk amplifier. This amplifier uses two diode arrays as pump source. A non-imaging lens duct is used to couple the radiation from the laser diode arrays to the laser disk. Preliminary result shows that the efficiency of this laser can be as high as 3 %, a factor of three increases over side-pump configuration. This high energy, highly efficient and high beam quality laser is a promising candidate for use in an efficient, multiple lidar applications.
Global wind measurement is a key component of weather prediction. Coherent wind lidar provides excellent wind profile measurement sensitivity and accuracy through the use of heterodyne detection technique. A high pulse energy, high beam quality, very narrow linewidth laser is essential for successful coherent wind detection. We have developed an eye- safe all solid state Ho:Tm:YLF power oscillator with ring configuration to be used as coherent lidar transmitter. It achieved an optical to optical efficiency of 0.03. A Q- switched output energy as high as 109 mJ at 6 Hz, with a pulse width of 170 ns is obtained. The resonator alignment sensitivity, heat dissipation efficiency and polarization extinction ratio are all characterized for space application lidar. Laser performance as a function of laser rod temperature and pump intensity has also been investigated. The high power and high beam quality of this laser make it well suited for use as a coherent wind lidar transmitter on a space platform.
Laser remote sensing technique using coherent lidar systems are being widely used for wind measurements. Laser wind measurements use the Doppler shift of backscattered radiation to determine the wind speed. To measure the small Doppler shifts accurately heterodyne detection is used. This technique requires an energetic, low divergence, narrow linewidth laser transmitter to maintain a high degree of coherence. For measurements from ground, air, or space platform, a reliable, all solid-state laser transmitter in the eye-safe region with appreciable energy/pulse is required. This paper reports development and performance of a diode-pumped solid-state amplifiers at 2-micrometer. Q-switched, 400-ns pulses with output energy of 700 mJ at 2-micrometer, representing an optical-to-optical efficiency of 2%, was achieved from five diode-pumped Ho:TM:YLF laser amplifiers at room-temperature.
The Lidar In-Space Technology Experiment (LITE) laser transmitter module (LTM) flight laser optical architecture has been space qualified by extensive testing at the system, subsystem, and component level. The projected system output performance has been verified using an optically and electrically similar breadboard version of the laser. Parasitic lasing was closely examined and completely suppressed after design changes were implemented and tested. Oscillator and amplifier-type heads were separately tested to 150 million shots. Critical subassemblies have undergone environmental testing to shuttle qualification levels. A superior three-color anti reflection coating was developed and tested for use on 14 surfaces after the final amplifier.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.