Broadband Mid-infrared Frequency Combs Generated via Frequency Division

Frequency combs have revolutionized metrology and demonstrated numerous applications in science and technology. Combs operating in the mid-infrared region could be beneficial for molecular spectroscopy for several reasons. First, numerous molecules have their spectroscopic signatures in this region. Furthermore, the atmospheric window (3-5μm and 8-14μm) is located here. Additionally, a mid-infrared frequency comb could be employed as a diagnostic tool for the many components of human breath, as well as for detection of harmful gases and contaminants in the atmosphere. In this thesis, I used synchronously pumped subharmonic optical parametric oscillators (OPOs) operating at degeneracy to produce ultra-broadband outputs near half of the pump laser frequency. One attractive property of the subharmonic OPOs is that the signal/idler waves of the OPO are frequency- and phase-locked to the pump frequency comb. We explored three new nonlinear materials in the subharmonic OPO and demonstrated a broadband spectrum for mid-infrared frequency comb generation. (1) Orientation-patterned (OP) gallium arsenide (GaAs) was selected as the first material because it has high nonlinearity. We found that the OP-GaAs based OPO yielded an approximately two-octave wide spectrum (2.8–11μm). (2) Gallium phosphide (GaP) has near zero group velocity dispersion (GVD) at 4.7 μm and a large bandgap. The OP-GaP OPO yielded a spectrum of more than two octaves (3–12.5μm). Also, because of the large bandgap, GaP is suitable for telecom 1.56-μm pumping, having the advantage of much smaller GVD than in periodically-poled-lithium-niobite (PPLN). The telecom laser (1.56μm) pumped OP-GaP OPO was demonstrated with more than one octave wide spectrum. (3) Finally, we explored the phenomenon of random phase matching in the zinc selenide (ZnSe) polycrystalline material. The first random phase matched OPO was demonstrated with more than one octave spectrum (3.1– 9μm), which is also the first OPO based on ZnSe

Background-free broadband absorption spectroscopy based on interferometric suppression with a sign-inverted waveform

Background-free methods have potentially superior detection sensitivity because of their ability to take advantage of the full laser power; they are therefore attractive to spectroscopists. We implement background-free Fourier transform spectroscopy based on coherent suppression of the background using an interferometer, whereby the central peak of the interferogram is suppressed without losing molecular absorption signatures. This results in the appearance of peaks rather than dips in the measured spectrum. The technique can be used with a variety of broadband spectroscopies and features advantages such as a reduction in the required detector dynamic range, the capability to perform quantitative measurements, and strongly enhanced sensitivity down to the quantum limit. We validated our method experimentally by performing mid-infrared dual-comb spectroscopy with a mixture of multiple molecular species over a broad wavelength range of 3-5 mu m. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing AgreementPeer reviewe

Optical Parametric Oscillation In A Random Poly-Crystalline Medium: Znse Ceramic

We demonstrate an optical parametric oscillator (OPO) based on random phase matching in a polycrystalline χ(2) material, ZnSe. The subharmonic OPO utilized a 1.5-mm-long polished ZnSe ceramic sample placed at the Brewster\u27s angle and was synchronously pumped by a Kerr-lens mode-locked Cr:ZnS laser with a central wavelength of 2.35 μm, a pulse duration of 62 fs, and a repetition frequency of 79 MHz. The OPO had a 90-mW pump threshold, and produced an ultrabroadband spectrum spanning 3-7.5 μm. The observed pump depletion was as high as 79%. The key to success in achieving the OPO action was choosing the average grain size of the ZnSe ceramic to be close to the coherence length (∼ 100 μm) for our 3-wave interaction. This is the first OPO that uses random polycrystalline material with quadratic nonlinearity and the first OPO based on ZnSe. Very likely, random phase matching in ZnSe and similar random polycrystalline materials (ZnS, CdS, CdSe, GaP) represents a viable route for generating few-cycle pulses and multi-octave frequency combs, thanks to a very broadband nonlinear response

Optical Parametric Oscillation In Random Polycrystalline Χ\u3csup\u3e(2)\u3c/sup\u3e Medium

We demonstrate the first OPO based on random phase matching. The OPO was based on ZnSe ceramic pumped by 62-fs, λ=2.35-μm Cr:ZnS laser pulses, had 90-mW pump threshold and produced an ultra-broad spectrum spanning 3-7.5 μm

Half-Watt Average Power Femtosecond Source Spanning 3–8 µm Based On Subharmonic Generation In Gaas

Frequency combs with a wide instantaneous spectral span covering the 3–20 µm molecular fingerprint region are highly desirable for broadband and high-resolution frequency comb spectroscopy, trace molecular detection, and remote sensing. We demonstrate a novel approach for generating high-average-power middle-infrared (MIR) output suitable for producing frequency combs with an instantaneous spectral coverage close to 1.5 octaves. Our method is based on utilizing a highly-efficient and compact Kerr-lens mode-locked Cr2+:ZnS laser operating at 2.35-µm central wavelength with 6-W average power, 77-fs pulse duration, and high 0.9-GHz repetition rate; to pump a degenerate (subharmonic) optical parametric oscillator (OPO) based on a quasi-phase-matched GaAs crystal. Such subharmonic OPO is a nearly ideal frequency converter capable of extending the benefits of frequency combs based on well-established mode-locked pump lasers to the MIR region through rigorous, phase- and frequency-locked down conversion. We report a 0.5-W output in the form of an ultra-broadband spectrum spanning 3–8 µm measured at 50-dB level

Half-Watt Average Power Compact Femtosecond Source With A Bandwidth Of 3-8 Μm Based On Subharmonic Gaas Opo

High-power (0.5 W) mid-IR output suitable for ultra-broadband frequency comb generation was produced in a subharmonic GaAs optical parametric oscillator that was synchronously pumped by a compact 0.9 GHz, 6 W femtosecond Cr:ZnS (2.35μm) MOPA

Optical Parametric Oscillation In A Random Polycrystalline Medium

We demonstrate an optical parametric oscillator (OPO) based on random phase matching in polycrystalline ZnSe. The OPO was pumped by Cr:ZnS laser pulses (2.35 μm, 62 fs, 79 MHz), had a pump threshold of 90 mW, and produced an ultrabroadband spectrum spanning 3–7.5 μm

Optical Parametric Oscillation In Random Polycrystalline Χ\u3csup\u3e(2)\u3c/sup\u3e Medium

We demonstrate the first OPO based on random phase matching. The OPO was based on ZnSe ceramic pumped by 62-fs, λ=2.35-μm Cr:ZnS laser pulses, had 90-mW pump threshold and produced an ultra-broad spectrum spanning 3-7.5 μm

Self-Referenced Octave-Wide Subharmonic Gap Optical Parametric Oscillator Centered At 3 Μm And Pumped By An Er-Fiber Laser

We report an octave-wide mid-IR spectrum (2.3–4.8 μm) obtained from a subharmonic optical parametric oscillator (OPO) based on a newly developed nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP), which was synchronously pumped by a femtosecond 1560 nm fiber laser. We proved that the octave-wide output is in the form of a single frequency comb. The observed f -to-2f frequency beats, originating directly from the OPO, can be used for self-referencing and phase locking of the pump laser comb with no need for supercontinuum generation. With an average output power of ∼30 mW, this setup might be beneficial for a variety of spectroscopic applications in the mid-IR

Half-Watt Average Power Compact Femtosecond Source With A Bandwidth Of 3-8 Μm Based On Subharmonic Gaas Opo

High-power (0.5 W) mid-IR output suitable for ultra-broadband frequency comb generation was produced in a subharmonic GaAs optical parametric oscillator that was synchronously pumped by a compact 0.9 GHz, 6 W femtosecond Cr:ZnS (2.35μm) MOPA