The development of parametric devices down-converting the laser frequency to the mid-infrared (3–30µm) based on non-oxide nonlinear optical crystals is reviewed. Such devices, pumped by solid-state ...laser systems operating in the near-infrared, fill in this spectral gap where no such lasers exist, on practically all time scales, from continuous-wave to femtosecond regime. All important results obtained so far with difference-frequency generation, optical parametric oscillation, generation and amplification are presented in a comparative manner, illustrating examples of recent achievements are given in more detail, and some special issues such as continuum and frequency comb generation or pulse shaping are also discussed. The vital element in any frequency-conversion process is the nonlinear optical crystal and this represents one of the major limitations for achieving high energies and average powers in the mid-infrared although the broad spectral tunability seems not to be a problem. Hence, an overview of the available non-oxide nonlinear optical materials, emphasizing new developments such as wide band-gap, engineered (mixed), and quasi-phase-matched crystals, is also included.
► The development of parametric down-conversion devices operating from 3 to about 20
μm is reviewed. ► All time scales, from continuous wave to femtosecond regime, are considered. ► An overview of ...the available non-oxide mid-infrared nonlinear optical materials is also included.
The development of parametric down-conversion devices operating in the mid-infrared, from 3
μm to about 20
μm, based on non-oxide nonlinear optical crystals is reviewed. Such devices, pumped by solid-state laser systems operating in the near-infrared, fill in this spectral gap where no solid-state laser technology exists, on practically all time scales, from continuous-wave to femtosecond regime. The vital element in any frequency-conversion process is the nonlinear optical crystal and this represents one of the major limitations with respect to achieving high energies and average powers in the mid-infrared although the broad spectral tunability seems not to be a problem. Hence, an overview of the available mid-infrared nonlinear optical materials, emphasizing new developments like wide band-gap, engineered (mixed), and quasi-phase-matched crystals, is also included.
High-brightness sources of coherent and few-cycle-duration light waveforms with spectral coverage from the ultraviolet to the terahertz would offer unprecedented versatility and opportunities for a ...wide range of applications from bio-chemical sensing1 to time-resolved and nonlinear spectroscopy, and to attosecond light-wave electronics2,3. Combinations of various sources with frequency conversion4,5 and supercontinuum generation6–9 can provide relatively large spectral coverage, but many applications require a much broader spectral range10 and low-jitter synchronization for time-domain measurements11. Here, we present a carrier-envelope-phase (CEP)-stable light source, seeded by a mid-infrared frequency comb12,13, with simultaneous spectral coverage across seven optical octaves, from the ultraviolet (340 nm) into the terahertz (40,000 nm). Combining soliton self-compression and dispersive wave generation in an anti-resonant-reflection photonic-crystal fibre with intra-pulse difference frequency generation in BaGa2GeSe6, the spectral brightness is two to five orders of magnitude above that of synchrotron sources. This will enable high-dynamic-range spectroscopies and provide numerous opportunities in attosecond physics and material sciences14,15.Using a gas-filled anti-resonant-reflection photonic-crystal fibre, a high-brightness table-top source of coherent carrier-envelope-phase-stable waveforms is demonstrated across seven octaves (340 nm to 40,000 nm) with ultraviolet peak powers up to 2.5 MW and terahertz peak powers of 1.8 MW, without the need for changing nonlinear crystals.
A Tm-doped mixed sesquioxide ceramic laser is mode-locked near 2 µm using InGaAsSb quantum-well semiconductor saturable absorber and chirped mirrors for dispersion compensation. Maximum average ...output power of 175 mW is achieved for a pulse duration of 230 fs at a repetition rate of 78.9 MHz with a 3% output coupler. Applying a 0.2% output coupler pulses as short as 63 fs are generated at 2.057 µm.
Nonlinear vibrational spectroscopy profits from broadband sources emitting in the molecular fingerprint region. Yet, broadband lasers operating at wavelengths above 7 μm have been lacking, while ...traditional cascaded parametric frequency down-conversion schemes suffer from exceedingly low conversion efficiencies. Here we present efficient, direct frequency down-conversion of femtosecond 100-kHz, 1.03-μm pulses to the mid-infrared from 7.5 to 13.3 μm in a supercontinuum-seeded, tunable, single-stage optical parametric amplifier based on the wide-bandgap material Cd
Hg
Ga
S
. The amplifier delivers near transform-limited, few-cycle pulses with an average power > 30 mW at center wavelengths between 8.8 and 10.6 μm, at conversion efficiencies far surpassing that of optical parametric amplification followed by difference-frequency generation or intrapulse difference-frequency generation. The pulse duration at 10.6 μm is 101 fs corresponding to 2.9 optical cycles with a spectral coverage of 760-1160 cm
. Cd
Hg
Ga
S
is an attractive alternative to LiGaS
and BaGa
S
in small-scale, Yb-laser-pumped, few-cycle mid-infrared optical parametric amplifiers and offers a much higher nonlinear figure of merit compared to those materials. Leveraging the inherent spatial variation of composition in Cd
Hg
Ga
S
, an approach is proposed to give access to a significant fraction of the molecular fingerprint region using a single crystal at a fixed phase matching angle.
Temperature tuning of CdSe optical parametric oscillators (OPO’s) is studied by pumping with the 1.8645-µm signal and 2.4793-µm idler outputs of a Nd:YAG laser-pumped CsTiOAsO 4 (CTA) OPO. The ...measured temperature-dependent phase-matching conditions are used to construct new Sellmeier and thermo-optic dispersion formulas for CdSe, which are verified via temperature-tuned sum-frequency generation (SFG) between the fundamental and second harmonic of a transversely excited atmospheric (TEA) CO 2 laser operating at 10.2466, 9.5525, and 9.2714 µm.
We demonstrate a dual-beam infrared optical parametric source featuring a noncollinear KTA booster amplifier and straightforward angular dispersion compensation of the idler beam. Through careful ...beam and pulse characterization, and high-harmonic generation in a crystalline solid, we show that the corrected idler beam is diffraction-limited, astigmatism-free, and compressible to its transform-limited, 5-cycle pulse duration. Pumped by only 40-µJ pulses at 1.03 µm, the parametric source delivers 7.8-µJ, 38-fs, 1.53-µm and 2.3-µJ, 53-fs, CEP-stable, 3.1-µm pulses at a repetition rate of 100 kHz. The scheme provides a promising route to scale the pulse energy and average power beyond PPLN- or KTA-based collinear OPA architectures.
We demonstrate a scheme for correcting the angular dispersion of the 3.1-<inline-formula><tex-math notation="LaTeX"> \mu</tex-math></inline-formula>m idler beam from a high repetition rate, ...KTiOAsO<inline-formula> <tex-math notation="LaTeX">_4</tex-math></inline-formula> (KTA) based noncollinear optical parametric amplifier pumped at 1.03 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>m and seeded by broadband signal pulses at 1.55 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>m. Following angular dispersion correction, successful temporal chirp compensation was possible, and a close to transform-limited pulse duration of 70 fs and a pulse energy of 30 <inline-formula><tex-math notation="LaTeX"> \mu</tex-math></inline-formula>J at a repetition rate of 100 kHz were obtained. The angular chirp compensated KTA-based scheme is scalable to higher pulse energies and average powers and has various advantages compared to periodically poled and angle-tuned LiNbO<inline-formula><tex-math notation="LaTeX">_3</tex-math></inline-formula> -based amplifiers, which exhibit low resistance to photorefractive damage.
PDF
