Optical Sciences and Photonics are areas of growing importance that are too often missing from traditional undergraduate science and engineering curricula. Often, aspects of optics and photonics are picked up as side topics in undergraduate and graduate courses along the way to obtaining more traditional STEM (Science, Technology, Engineering and Mathematics) degrees. Since 2016, the annual Optical Sciences Winter School has been held during the winter break of the University of Arizona’s academic calendar. Its annual participants are now approximately 50 – 60 undergraduate students (mostly juniors and seniors) from US (United States) Universities who demonstrate an aptitude and talent for science and research. These students participate in a three- to five-day immersion experience, learning the many opportunities and benefits that choosing optics and photonics for their graduate studies can offer. The Optical Sciences Winter School (OSWS) brings together a motivated group of undergraduate students for a series of overview lectures teaching foundational topics in optics and their relation to current research. It also provides a forum for faculty, alumni, and invited guests to share results, approaches and methodologies in optics and photonics research and education that are unique to the undergraduate setting. This event is not focused on a specific school’s program but tries to highlight the diverse optics programs in the US. Many sessions in the program are filled with various invited faculties and researchers’ presentations from prominent optical physics and engineering undergraduate or graduate institutions.
We build and model coupled GHz rep rate mode-locked VECSEL cavities sharing a common gain medium. The goal is to understand both experimentally and theoretically, gain competition between pulse trains in each cavity while varying relative rep rates and explore applications.
A mode-locked VECSEL is reported using a novel hybrid semiconductor saturable absorber mirror (SESAM) consisting of a semiconductor absorber region bonded to a curved dielectric partial reflector. The hybrid SESAM is realized by direct bonding of the saturable absorber to a commercially available ultrafast output coupler, nominally 99.4% reflectivity and GDD of ≤ |20 fs2| with a radius of curvature of 10 cm. In a linear cavity where the curved output coupler is the hybrid SESAM, a pulse-width of 410 femtoseconds is achieved at a repetition rate of 4.2 GHz for a VECSEL operating at a wavelength of 1030 nm.
Mid infrared frequency combs allow for high resolution absorption spectroscopy of molecular species, which have strong signatures in this spectral region. Dual comb spectroscopy can provide broadband and high-resolution capability, but requires two fully stabilized frequency combs which adds complexity to the system.
Previous work has demonstrated that frequency combs coupled with a high resolution spectrometer, consisting of a virtually imaged phased array (VIPA) along with a grating, can perform time-resolved, broadband and high- resolution absorption spectroscopy with a single frequency comb. The VIPA spectrometer disperses the spectrum in two dimensions and images it onto a focal plane detector array. If the comb teeth can be resolved, the VIPA is easily calibrated and provides comb-tooth resolved resolution and accuracy. However, in previous work, the repetition rate of the laser sources used was too low to be resolved directly, and additional passive "filter cavities" had to be employed to increase the effective repetition rate of the frequency comb. In this work we use a fully stabilized mid infrared frequency comb based on a 1.6 GHz repetition rate modelocked vertical external cavity surface emitting laser (VECSEL) and difference frequency generation to produce an off set free comb in the 3- 4 micron wavelength range. The source is directly coupled to the VIPA spectrometer to provide comb-tooth resolved absorption spectroscopy. We discuss the system's performance in gas absorption spectroscopy and its time resolving capabilities, which are limited only by the speed of the detector system.
The mid-infrared (MIR) region above 3 microns is of great interest for spectroscopic applications. Because it is difficult to produce mode-locked laser sources that emit natively in this region, difference frequency generation (DFG) is a popular method to produce mid-IR output using more traditional laser oscillators. Previous examples include fiber based DFG sources and OPOs, which are typically limited to repetition rates on the order of tens to hundreds of MHz. VECSELs allow access to higher repetition rates, while the use of highly nonlinear waveguides enables the requisite spectral broadening despite the lower pulse energy. In this work we present a VECSEL-based frequency comb that uses DFG to produce output in the 3-4 micron range. This system is based on a mode-locked VECSEL emitting at a 1030 nm wavelength with a 1.6 GHz repetition rate. A Yb fiber amplification system is used to increase the power to over 10W and compress the pulses to sub-90 fs. Coherent spectral broadening out to 1560 nm is achieved with a nonlinear waveguide. By combining the 1030 nm and 1560 nm beams in a PPLN DFG crystal, 290 mW of mid IR output between 3.0 and 3.5 microns is produced. Since the DFG light is produced by two wavelengths from the same oscillator, the carrier envelope offset frequency is cancelled, producing an offset free comb requiring stabilization of only a single degree of freedom. We characterize this VECSEL based frequency comb and discuss the advantages it provides for spectroscopic applications.
We present preliminary results showing the potential of VECSEL technology for the generation of high power coherent supercontinuum. Among these results, we demonstrate a stable output power of 16 W with a pulse duration of 71 fs and a repetition rate of 1.7 GHz from a VECSEL oscillator and Ytterbium fiber amplifier. This system was used to generate a coherent supercontinuum averaging 3 W of power using a highly nonlinear photonic crystal fiber. In addition, we discuss the possible methods for the detection and stabilization of the carrier offset frequency. The beatnote between a VECSEL seeded supercontinuum and an external CW laser reveals a relatively stable signal, well above the detection noise. A discussion about system design considerations for noise reduction and increased offset frequency stability is also included.
We present a novel Vertical External Cavity Surface Emitting Laser (VECSEL) cavity design which makes use of multiple interactions with the gain region under different angles of incidence in a single round trip. This design allows for optimization of the net, round-trip Group Delay Dispersion (GDD) by shifting the GDD of the gain via cavity fold angle while still maintaining the high gain of resonant structures. The effectiveness of this scheme is demonstrated with femtosecond-regime pulses from a resonant structure and record pulse energies for the VECSEL gain medium. In addition, we show that the interference pattern of the intracavity mode within the active region, resulting from the double-angle multifold, is advantageous for operating the laser in CW on multiple wavelengths simultaneously. Power, noise, and mode competition characterization is presented.
We present a comprehensive characterization of semiconductor gain and absorber devices utilizing novel measurement techniques. Using a 20fs probe laser, a time resolution in the few femtosecond range is achieved in traditional pump and probe measurements performed on VECSELs and SESAMs. In-situ characterizations of VECSEL samples mode-locked in the sub-500fs regime reveal the fast and longtime recoveries of the gain present in real lasing conditions. Spectrally-resolved probing gives further information about the properties of carriers in VECSEL gain media. Our results indicate that stable mode-locked operation is sustained by multiple carrier relaxation mechanisms ranging from a few femtoseconds to the pico- and nanosecond regimes.
While Vertical-External-Cavity-Surface-Emitting-Lasers (VECSELs) have been successfully used as ultrafast laser sources with pulse durations in the hundreds of femtosecond regime, the dynamics within the semiconductor gain structure are not yet completely understood. With the high carrier densities inside the semiconductor, nonequilibrium effects such as kinetic-hole burning are expected to play a major role in pulse formation dynamics. Moreover, the nonlinear phase change by the intense light field can induce a complex dispersion, which may potentially limit the achievable pulse durations. To shed light on such nonequilibrium dynamics, we perform in-situ characterization of mode-locked VECSELs. We probe the gain media as well as the intracavity absorber with a femtosecond fiber laser source. For measuring temporal characteristics, we employ an asynchronous optical sampling technique by phase-locking the repetition rate of the VECSEL to a multiple of the probe laser with an adjustable offset frequency. This allows for probing dynamics from femtosecond to nanosecond time scales with scan rates up to hundreds of Hertz without compromise of measurement precision which can be introduced by mechanical delays covering such large temporal windows. With a resolution in the femtosecond range, we characterize gain depletion by the intracavity pulse as well as the gain recovery timescales for different power levels and operation regimes.
We demonstrate the utility of optically pumped semiconductor lasers (OPSLs) in the eld of precision atomic spectroscopy. We have constructed an OPSL for the purpose of laser-cooling and trapping neutral Hg atoms. The OPSL lases at 1015 nm and is frequency quadrupled to provide the trapping light for the ground state cooling transition. We report up to 1.5 W of stable, single-frequency output power with a linewidth of < 70 kHz with active feedback. From the OPSL we generate deep-UV light at 253.7 nm used to form a neutral Hg magneto-optical trap (MOT). We present details of the MOT. We also report initial results for spectroscopy of the 61S0 - 63P0 clock transition in the Hg199 isotope.
The dynamic intracavity ionization of a dilute gas target can substantially alter the pulse formation inside
resonant fs enhancement cavities. We numerically and experimentally study these effects and how they affect
intracavity high harmonic generation using fs frequency combs.
We propose a method of optical data storage that exploits the small dimensions of metallic nano-particles
and/or nano-structures to achieve high storage densities. The resonant behavior of these particles (both individual and in
small clusters) in the presence of ultraviolet, visible, and near-infrared light may be used to retrieve pre-recorded
information by far-field spectroscopic optical detection. In plasmonic data storage, a femtosecond laser pulse is focused
to a diffraction-limited spot over a small region of an optical disk containing metallic nano-structures. The digital
information stored in each bit-cell modifies the spectrum of the femtosecond light pulse, which is subsequently detected
in transmission (or reflection) using an optical spectrum analyzer. We present theoretical as well as preliminary
experimental results that confirm the potential of plasmonic nano-structures for high-density optical storage applications.
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.