Second harmonic generation (SHG) is a ubiquitous technique for extending the spectral coverage of laser sources into regions that would otherwise be technologically challenging to access. SHG schemes typically rely on the use of bulk optical components, resulting in systems with large footprints requiring precise optical alignment. Integration of the SHG components into a single unit facilitates the implementation of compact, robust and turn-key sources, suitable for applications in biophotonic imaging, amongst others. We report on the development of fiber-coupled frequency doubling modules and their application to novel fiberintegrated picosecond pulse sources in the visible and near-visible. The modules employ a simple, single-pass configuration using a periodically-poled lithium niobate (PPLN) crystal as the nonlinear conversion medium. They are readily adaptable for different fiber pump laser configurations and are configurable with either fiber-coupled or collimated free-space outputs. Two sources using the modules are presented, operating at 780 nm and 560 nm. The 780 nm source utilizes an erbium master oscillator power fiber amplifier (MOPFA) scheme. SHG was performed in a 35 mm long crystal, generating 3.5 W of 780 nm radiation with a pulse duration of 410 ps at 50 MHz and conversion efficiencies exceeding 20%. Results of this source being used for parametric wavelength conversion in photonic crystal fiber are discussed. The 560 nm source was based on SHG of a Raman amplified CW diode pumped by a pulsed ytterbium-fiber MOPFA. This source generated 450 mW of average power with conversion efficiencies greater than 20%.
We present experimental data obtained during investigation of synchronously pumped optical parametric oscillators (SPOPO’s) pumped by fundamental (1030 nm) and second harmonic (515 nm) radiation of mode-locked Yb:KGW laser, providing 105 fs pulses at 76 MHz repetition rate with an average power of 4 W. Different nonlinear crystals such as beta barium borate (BBO), and periodically poled lithium niobate (PPLN) and MgO doped PPLN (MgO:PPLN) were tested to estimate wavelength tuning capabilities and SPOPO’s efficiency. Rotation of BBO nonlinear crystal and SPOPO’s cavity length variation and, in the case of SPOPO based on PPLN, change of grating period and cavity length allowed signal wavelength tuning in 630 – 1030 nm and 1350 – 1700 nm spectral ranges, respectively. Parametric light conversion from pump power to signal power efficiency was as high as 25 %. Including the idler pulses the tuning ranges were from 630 to 2400 nm and from 1350 to 4000 nm in case of BBO and PPLN crystals, respectively. SPOPO based on BBO wsithout intracavity group velocity dispersion (GVD) compensation generates longer than transform limited pulses, so SPOPO based on BBO with dispersive prisms were investigated.
We report laser-induced damage threshold (LIDT) measurements of periodically poled lithium niobate (PPLN) and
magnesium-oxide-doped PPLN (MgO:PPLN) in the femtosecond pulse duration regime at 1030 nm with 100 kHz and 75
MHz repetition rate. PPLN and MgO:PPLN crystals with broadband Nb2O5/SiO2 AR coatings for 1.4 - 1.8 um spectral
range were used. S-on-1 test for LIDT measurements were performed. S was equal to 106 and 4.56*1010 pulses for 100
kHz CPA laser system and 75 MHz oscillator, respectively. Evaluated LIDT was 20 mJ/cm2 for 290 fs pulses at 100 kHz repetition rate and 0.63 mJ/cm2 for 105 fs pulses at 76 MHz repetition rate.
We report the absorption and scattering losses measurements in IR range by high average power tunable radiation of optical parametric oscillator (OPO) based on a periodically poled lithium niobate (PPLN) pumped by a diode-pumped, Q-switched TEM00 mode Nd:YVO4 laser operated at 1064 nm.
Techniques are presented to model optical nonlinear frequency conversion of highly distorted beams with M-squared values as high as 30. Random superpositions of Gaussian-Hermite modes are used to create the field distributions of the incident beams. Split-step Fourier transform techniques are used for the calculation of nonlinear conversion.
We report the optimisation of a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) pumped by a diode-pumped, Q-switched multiaxial TEM00 mode Nd:YAG laser operated at 1064 nm. Total conversion efficiency exceeding 66 % was achieved. This OPO is used in a coherent spectrophotometer for optical component characterisation.
A review of measurement techniques and nonlinear coefficient values are presented. Coefficients of a few materials are evolving as standards by consensus based on independent measurements. Improved instrumentation, extension of measurement techniques, and more detailed analysis are improving accuracy in recent measurements. Confusion still remains for values of some materials, and specification of the reporting frame for the tensor values remains an issue.
We report on the development and use of coherent spectrophotometers specialized for the unusual requirements of characterizing nonlinear optical materials and multilayer dielectric coatings used in laser systems. A large dynamic range is required to measure the linear properties of transmission, reflection and absorption and nonlinear properties of laser-induced damage threshold and nonlinear frequency conversion. Optical parametric oscillators generate coherent radiation that is widely tunable with instantaneous powers that can range from milliwatts to megawatts and are well matched to this application. As particular example a laser spectrophotometer based on optical parametric oscillators and a diode-pumped, Q-switched Nd:YAG laser and suitable for optical characterization in the spectral range 420-4500 nm is described. Measurements include reflectance and transmittance, absorption, scattering and laser-induced damage thresholds. Possibilities of a system based on a 130-fs Ti:sapphire laser and optical parametric generators are also discussed.
A laser spectrophotometer based on optical parametric oscillators for characterization of optical coatings in the spectral range 420 - 4500 nm is described. The characterization includes measurements of reflectance and transmittance, absorption losses, and laser-induced damage thresholds. The master oscillator of the pump-laser system is a diode-pumped, Q-switched Nd:YAG laser. Additional power, when needed for laser-induced damage threshold measurements, is obtained from flashlamp-pumped Nd:YAG amplifiers. Operation of the laser spectrometer is demonstrated by absorptance measurements and reflectance and transmission measurements of optical coatings over a wide range of angle of incidence. Damage thresholds are measured both with the OPO output and with the direct output and harmonics of the output of the amplified laser system.
Measurements on several high-reflection (HR) metallic mirrors were performed, and multiple-pulse laser induced damage thresholds (LIDT) were estimate according to the draft International Standard ISO/DIS 11254 using S on 1 tests at 1064 nm. The experimental set-up was based on Q-switched, diode-pumped Nd:YAG laser. Transmission increase was used for an in situ measurement of damage. The characteristic damage curves were plotted and multiple-pulse damage thresholds were determined at 30-Hz pulse-repetition rate, while the number of pulses varied up to 300.
We report polarization dependent measurements of absorptance of some crystal performed according to the ISO11551 standard by the 'pulse' or 'gradient' calorimetric method at 1064 and 532 nm using a pulsed, diode-pumped, Q-switched YAG:Nd laser.
We report the optimization of a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) pumped by a diode-pumped, Q-switched Nd:YAG laser operated at 1064 nm. Total conversion efficiency exceeding 66 percent was achieved.
We review progress on quasi-phasematched optical parametric oscillators (OPOs) in bulk periodically poled LiNbO3. We have extended the electric-field poling process so that we now reliably fabricate crystals over 60-mm long in full 3-inch-diameter, 0.5-mm-thick wafers. Periodically poled material retains the low loss and bulk power handling properties of single domain LiNbO3, and QPM allows noncritical phasematching with the highest value of the nonlinear coefficient. OPOs pumped by 1.064-micrometers Nd:YAG lasers have been operated over the wavelength range 1.36 micrometers to 4.9 micrometers with tuning by temperature or QPM period. We have shown oscillation threshold as low as 0.006 mJ with a Q-switched pump laser, and pumping over 25 times threshold without damage. We have also demonstrated a doubly resonant OPO pumped directly with a commercial cw diode laser at 978 nm, and a 1.064-micrometers -pumped cw singly-resonant OPO with threshold < 3 W.
The use of nonlinear infrared frequency conversion of laser output for infrared scene projection is explored. Nonlinear frequency conversion can be used to shift a laser wavelength for scanned laser images or used for two-dimensional image conversion in which an image in one spectral region such as the visible is projected as an image at a different wavelength in the IR.
We review progress of quasi-phasematched (QPM) optical parametric oscillators (OPOs) in bulk periodically poled LiNbO3. Using the electric field poling process, we can reliably fabricate 0.5-mm thick crystals with uniform domain structures over 15-mm long. Periodically poled material retains the low loss and bulk power handling properties of single domain LiNbO3, and QPM allows noncritical phasematching with the highest value of the nonlinear coefficient. OPOs pumped by 1.064-micrometers pulsed Nd:YAG lasers have been operated over the wavelength range 1.45 micrometers to 4.0 micrometers with tuning by temperature or QPM period. We have shown oscillation threshold as low as 0.020 mJ with a Q-switched pump laser, and pumping over two times threshold without damage. We have also demonstrated a doubly resonant oscillator near 1.96 micrometers pumped directly with a cw diode laser at 978 nm.
We are developing the diffusion-bonded stacked (DBS) structure for quasi-phasematched interactions to meet the need for high- power nonlinear conversions in the infrared. In our preliminary investigations, we have compared optical and thermal properties of some potential DBS materials. Theoretical projections of device performance were compared for DBS GaAs and ZnSe and birefringent crystals ZnGeP2 and AgGaSe2 for both second- harmonic generation (SHG) of 10-micrometers radiation and 2-micrometers pumped optical parametric oscillators (OPOs). We are refining bonding processes for GaAs and have initial diffusion bonding results for ZnSe. We have fabricated and tested DBS GaAs structures for SHG, demonstrating that the crystal orientation is conserved during the bonding process, and that the nonlinear generation of the individual layers sums coherently. These studies indicate that DBS materials have potential for application in high-average-power OPOs.
A wide range of nonlinear optical coefficients and various systems of notation have been used to describe optical second-harmonic generation (SHG). To avoid possible confusion, the techniques of optical nonlinear coefficient measurement and the elementary theory of SHG are briefly reviewed. Absolute and relative nonlinear coefficient measurements by phase-matched SHG are described. The following results were obtained: d36(KDP) equals 0.38 pm/V, d36(KD*P) equals 0.37 pm/V, d22(BaB2O4) equals 2.2 pm/V, d31(LiIO3) equals -4.1 pm/V, d31(5%MgO:LiNbO3) equals -4.7 pm/V, d15(KTP) equals 1.9 pm/V and d24(KTP) equals 3.5 pm/V. The accuracy of these measurements is estimated to be better than 10%. An example of high-repetition-rate pulsed SHG in AgGaSe2 is given to demonstrate the use of quantitative analysis of harmonic generation for evaluation of nonlinear optical material performance.
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications IX
25 January 2010 | San Francisco, California, United States
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications VIII
27 January 2009 | San Jose, California, United States
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications VII
22 January 2008 | San Jose, California, United States
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications VI
23 January 2007 | San Jose, California, United States
Laser Sources and Enabling Materials
13 June 2006 | Dayton, Ohio, United States
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications V
25 January 2006 | San Jose, California, United States
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications IV
26 January 2005 | San Jose, California, United States
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications III
26 January 2004 | San Jose, Ca, United States
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications II
27 January 2003 | San Jose, CA, United States
Nonlinear Optics for High-Speed Electronics and Optical Frequency Conversion/Nonharmonic Optical Frequency Conversion: Parametric Oscillatiors and Related Devices
26 January 1994 | Los Angeles, CA, United States
Nonlinear Optics for High-Speed Electronics and Optical Frequency Conversion
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