ABSTRACT
The highly-nonlinear chalcopyrite crystal family has experienced remarkable success as source crystals in the mid-infrared spectral range, such that these crystals are primary candidates for producing high terahertz frequency (i.e., [Formula: see text] 10 THz) electric fields. A phase-resolved terahertz electric field pulse is produced via intra-pulse difference frequency generation in a chalcopyrite (110) ZnGeP2 crystal, with phase-matching being satisfied by the excitation electric field pulse having polarizations along both the ordinary and extraordinary crystal axes. While maximum spectral power is observed at the frequency of 24.5 THz (in agreement with intra-pulse phase-matching calculations), generation nonetheless occurs across the wide spectral range of 23-30 THz. To our knowledge, this is the first time a chalcopyrite ZnGeP2 crystal has been used for the generation of phase-resolved high-frequency terahertz electric fields.
ABSTRACT
We report on experimental demonstration of optical transient detection (OTD) based on photorefractive two-wave mixing of femtosecond pulses. The demonstrated technique also combines nonlinear-crystal-based OTD with up-conversion from infrared into the visible range. The approach enables measurement of phase changes of a dynamic signal in the infrared using GaP- or Si-based detectors while suppressing stationary background. Experimental results reveal existence of the relation between input phases in the infrared and output phases in the visible wavelength range. We further present experimental evidence of additional merits of up-converted transient phase analysis under noisy conditions, such as residual continuous-wave emission affecting the ultrashort pulses from the laser.
ABSTRACT
A phase-resolved electric field pulse is produced through the second-order nonlinear process of intra-pulse difference frequency generation (DFG) in a (110) CdSiP2 chalcopyrite crystal. The generated electric field pulse exhibits a duration of several picoseconds and contains frequency components within the high-frequency terahertz regime of â¼17-32 THz. The intra-pulse DFG signal is shown to be influenced by single-phonon and two-phonon absorption, the nonlinear phase-matching criterion, and temporal spreading of the excitation electric field pulse. To date, this is the first investigation in which a CdSiP2 chalcopyrite crystal is used to produce radiation within the aforementioned spectral range.
ABSTRACT
The potential of frequency comb spectroscopy has aroused great interest in generating mid-infrared frequency combs in the integrated photonic setting. However, despite remarkable progress in microresonators and quantum cascade lasers, the availability of suitable mid-IR comb sources remains scarce. Here, we generate mid-IR microcombs relying on cascaded three-wave-mixing for the first time. By pumping a CdSiP2 microresonator at 1.55 µm wavelength with a low power continuous wave laser, we generate χ(2) frequency combs at 3.1 µm wavelength, with a span of about 30 nm. We observe ordinary combs states with a line spacing of the free spectral range of the resonator, and combs where the sideband numbers around the pump and half-harmonic alternate, forming staggered patterns of spectral lines. Our scheme for mid-IR microcomb generation is compatible with integrated telecom lasers. Therefore, it has the potential to be used as a simple and fully integrated mid-IR comb source, relying on only one single material.
ABSTRACT
A GaSe crystal cut along the (001) crystallographic plane is investigated for the emission and detection of high-frequency (i.e. up to â¼20 THz) electric fields. To date, a comprehensive analysis on high-frequency difference frequency generation and electro-optic sensing in GaSe has not been performed and should consider aspects such as electric field polarization orientation, symmetries inherent to the crystal structure, and the various possible generation and detection phase-matching arrangements. Herein, terahertz radiation generation is investigated for various excitation electric field polarizations as the GaSe crystal is rotated in the (001) plane. Subsequently, the crystal is rotated out-of-plane to investigate the difference frequency generation and electro-optic sampling phase-matching conditions for various arrangements. The measured terahertz radiation spectra show peak generation at the frequencies of 10, 16, and 18 THz (dependent on the GaSe crystal orientation), in agreement with the frequencies exhibiting perfect phase-matching. GaSe has the potential to emerge as the primary crystal for the emission and detection of high-frequency electric fields, such that this comprehensive analysis is necessary for the widespread adoption and practical implementation of GaSe as a high-frequency source crystal.
ABSTRACT
Optical parametric oscillators (OPOs) constitute an important coherent, narrow-linewidth and widely tunable light source with applications in spectroscopy and many other fields. Their realizations based on whispering gallery resonators (WGRs) provide a small footprint and ultra-low thresholds, with demonstrations of tunability typically done via temperature variation. In this work, we show the pump tuning capabilities of a mm-sized WGR mid-infrared OPO made of CdSiP2. By tuning a telecom wavelength diode laser by 16 nm, we generate tunable light from 2708 to 3575 nm. Furthermore, we show controlled tuning in steps of 1 free spectral range (FSR) and the possibility of 12 GHz of continuous tuning. All these features are in good agreement with the theoretical predictions. We conclude that tuning from 2.4 to 4.9 µm is even possible, while still using commercially available near-infrared diode lasers. This work highlights the advantages of pump tuning of WGR OPOs and provides valuable insights for their precise control.
ABSTRACT
We report a seeded optical parametric generator (OPG) producing tunable radiation from 4.2-4.6 µm. The seeded OPG employs a 13 mm long CdSiP2 (CSP) crystal cut for non-critical phase-matching, pumped by a nanosecond-pulsed, MHz repetition rate Raman fiber amplifier system at 1.24 µm. A filtered, continuous-wave fiber supercontinuum source at 1.72 µm is used as the seed. The source generates up to 0.25 W of mid-infrared (MIR) idler power with a total pump conversion of 42% (combined signal and idler).
ABSTRACT
We report a subharmonic (frequency-divide-by-2) optical parametric oscillator (OPO) with a continuous wavelength span of 3 to 12 µm (-37dB level) that covers most of the molecular rovibrational "signature" region. The key to obtaining such a wide spectral span is the use of an OPO with a minimal dispersion-through the choice of intracavity elements, the use of all gold-coated mirrors, and a special "injector" mirror. The system delivers up to 245 mW of the average power with the conversion efficiency exceeding 20% from a 2.35 µm Kerr-lens mode-locked pump laser.
ABSTRACT
We report on narrowband terahertz (THz) radiation generation via optical rectification from a BaGa4Se7 crystal. The dense phonon mode distribution of the BaGa4Se7 crystal causes narrow transmission bands in the THz frequency range with enhanced nonlinear susceptibility magnitudes, thus permitting strong narrowband THz radiation generation at the frequencies of 1.97 and 2.34 THz. In comparison to THz radiation generated from a ZnTe crystal, the narrowband THz radiation produced by the BaGa4Se7 crystal is 4.5 times higher at 1.97 THz and 63% higher at 2.34 THz, thus making BaGa4Se7 a viable crystal for use in such areas as security and medicine.
ABSTRACT
Optical rectification is experimentally investigated in a biaxial BaGa4Se7 crystal by considering various combinations of near-infrared excitation polarizations and crystal orientations. The highest terahertz radiation is produced along the Z crystallo-physical direction of the BaGa4Se7 crystal. Despite the optical complexity of the BaGa4Se7 crystal in the terahertz spectral regime, this systematic experimental investigation determines the optimal excitation polarization and crystal orientation for the optical rectification process.
ABSTRACT
We report a synchronously-pumped femtosecond optical parametric oscillator (OPO) based on orientation-patterned gallium phosphide (OP-GaP), providing continuously tunable mid-infrared (mid-IR) idler radiation across 3570-7892 nm (2801-1267 cm-1), by exploiting pump wavelength tuning. We generate up to 54 mW of output average power at 80 MHz, and quantum conversion efficiencies up to 28.9% are achieved by use of synchronized pump retroreflection. With the inclusion of intracavity dispersion compensation in an OP-GaP OPO, near-transform-limited signal pulse durations of 112 fs at 1288 nm are measured, and peak powers up to 3 kW in the mid-IR are inferred. Finally, evidence of three-photon absorption is observed and characterized near the pump wavelength.
ABSTRACT
We report a pulsed singly-resonant optical parametric oscillator (OPO) based on the new nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched Nd:YAG laser at 1064 nm, and using a 40-mm-long OP-GaP crystal with a single grating period of Λ=16 µm, the OPO generates signal and idler output across 1.6-1.7 µm and 2.8-3.1 µm, respectively, under temperature tuning. For an average pump power of 4.8 W at 50 kHz pulse repetition rate, mid-infrared idler powers of up to â¼20 mW have been obtained at 2966 nm with high output stability. For pump pulses of â¼13 ns duration, the OPO generates â¼6 ns output signal pulses. From temperature-dependent wavelength tuning measurements at two different pump powers of 4.2 W and 1.2 W, a discrepancy of 11-17°C in the internal crystal temperature is estimated, implying that the OP-GaP sample suffers from increasing thermal effects at higher pump powers due to absorption.
ABSTRACT
We report the generation of tunable continuous-wave (cw) mid-infrared (mid-IR) radiation across 4608-4694 nm using the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). By exploiting difference-frequency mixing between a cw Tm-fiber laser and a home-built cw optical parametric oscillator in a 40-mm-long crystal, we have generated up to 43 mW of cw output power, with >30 mW across >95% of the mid-IR tuning range. The output at 4608 nm exhibits high beam quality with a passive power stability of 2.5% rms over 1.5 min. The temperature acceptance bandwidth of the OP-GaP crystal has been measured and compared with theory. The performance of the mid-IR source at high pump powers and polarization-dependent transmission in OP-GaP has been investigated.
ABSTRACT
We report a high-repetition-rate femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on type-I critical phase-matching in CdSiP2 (CSP), pumped directly by a Ti:sapphire laser. Using angle-tuning in the CSP crystal, the OPO can be continuously tuned across 7306-8329 nm (1201-1369 cm-1) in the deep-IR. It delivers up to 18 mW of idler average power at 7306 nm and >7 mW beyond 8000 nm at 80.5 MHz repetition rate, with the spectra exhibiting bandwidths of >150 nm across the tuning range. Moreover, the signal is tunable across 1128-1150 nm in the near-infrared, providing up to 35 mW of average power in â¼266 fs pulses at 1150 nm. Both beams exhibit single-peak Gaussian distribution in TEM00 spatial profile. With an equivalent spectral brightness of â¼5.6×1020photons s-1 mm-2 sr-10.1% BW-1, this OPO represents a viable alternative to synchrotron and supercontinuum sources for deep-IR applications in spectroscopy, metrology, and medical diagnostics.
Subject(s)
Cadmium Compounds/chemistry , Lasers , Optical Phenomena , Phosphorus Compounds/chemistry , Silicon Compounds/chemistry , Aluminum Oxide , TitaniumABSTRACT
We report the generation of tunable high-repetition-rate picosecond radiation in the mid-infrared using the new quasi-phase-matched nonlinear material of orientation-patterned gallium phosphide (OP-GaP). The source is realized by single-pass difference-frequency-generation (DFG) between the output signal of a picosecond optical parametric oscillator (OPO) tunable across 1609-1637 nm with input pump pulses at 1064 nm in OP-GaP, resulting in tunable radiation across 3040-3132 nm. Using a 40-mm-long crystal, we have generated up to 57 mW of DFG average power at ~80 MHz repetition rate for a pump power of 5 W and signal power of 0.9 W, with >30 mW over >50% of the tuning range. The DFG source exhibits a passive power stability better than 3.2% rms over 1 hour in good spatial beam quality. To the best of our knowledge, this is the first picosecond frequency conversion source based on OP-GaP.
ABSTRACT
We report on the generation of broadband (0.07-6 THz) terahertz (THz) radiation via optical rectification in a ⟨110⟩ CdSiP2 (CSP) crystal pumped by a 50 fs, 780 nm central wavelength optical pulse. By measuring the THz phase refractive index and the optical pump group refractive index, good phase matching can be achieved for a crystal thickness â²200 µm. Due to this crystal's high second order nonlinearity and low absorption losses, it is envisioned that THz generation from CSP could be further enhanced by confining the optical pump pulse to sub-wavelength waveguides.
ABSTRACT
We report a high-repetition-rate picosecond optical parametric oscillator (OPO) based on CdSiP2 (CSP) that is synchronously pumped by an Yb-fiber laser at 1064 nm and provides high average power in the deep-infrared (deep-IR) at 79.5 MHz. The OPO is tunable across 6205-6710 nm in the idler, providing as much as 105 mW of average power at 6205 nm and >55 mW over nearly the entire tuning range. The deep-IR idler output exhibits passive power stability better than 2.3% rms over 12 h in good beam quality. The near-IR signal pulses from the OPO have a Gaussian pulse duration of â¼19 ps, measured at 1284 nm. We have investigated the temperature tuning characteristics of the OPO and compared the data with the theoretical calculations using the most recent Sellmeier equations and thermo-optic coefficients for the crystal. To the best of our knowledge, this is the first picosecond OPO based on CSP operating at MHz repetition rates.
ABSTRACT
We report an optical parametric generator (OPG) based on the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched nanosecond Nd:YAG laser at 1064 nm with 25 kHz pulse repetition rate, the OPG can be tuned across 1721-1850 nm in the signal and 2504-2787 nm in the idler. Using a 40-mm-long crystal in single-pass configuration, we have generated a total average output power of up to â¼18 mW, with â¼5 mW of idler power at 2670 nm, for 2 W of input pump power. The OPG exhibits a passive stability in total output power better than 0.87% rms over 1 h, at a crystal temperature of 120°C, compared to 0.14% rms for the input pump. The output signal pulses, recorded at 1769 nm, have duration of 5.9 ns for input pump pulses of 9 ns. Temperature-dependent loss measurements for the pump polarization along the [100] axis in the OP-GaP crystal have also been performed, for the first time, indicating a drop in transmission from 28.8% at 50°C to 19.4% at 160°C.
ABSTRACT
We report on a high-power femtosecond optical parametric oscillator (OPO) at 80 MHz repetition rate, tunable across 6318-7061 nm in the deep-infrared (deep-IR) using pump wavelength tuning. The OPO, based on CdSiP2 (CSP), is synchronously pumped by a commercial Ti:sapphire-pumped femtosecond OPO in the near-IR, enabling rapid static tuning of the CSP OPO with minimal adjustments to its cavity length. The deep-IR CSP OPO provides as much as 32 mW of average idler power at 6808 nm with spectral bandwidth >1000 nm (at -10 dB level) across the tuning range. By implementing intracavity dispersion control, near-transform-limited signal pulses of â¼100 fs duration with smooth single-peak spectrum are achieved at 1264 nm, corresponding to an idler wavelength at 6440 nm. To the best of our knowledge, this is the first time such practical idler powers in the deep-IR have been generated from a dispersion-compensated CSP femtosecond OPO at sub-100 MHz repetition rate.
ABSTRACT
We study the temporal coherence of an ultrabroadband frequency comb produced in a degenerate GaAs optical parametric oscillator (OPO) pumped by a stabilized Tm-fiber comb, by observing multiheterodyne beats in the RF domain. We infer that in such a regime the OPO automatically produces a stable frequency comb that is phase and frequency locked to the pump. By varying intracavity dispersion, we achieve a comb spanning 2.6-7.5 µm at a -20 dB level. Low pump threshold (down to 7 mW), high average power (up to 73 mW), broad spectral coverage, flat spectrum, and high coherence make this comb a source suitable for various applications, foremost dual-comb molecular spectroscopy.