Laser-induced damage threshold of ZnGeP2 crystal for (sub)picosecond 1-µm laser pulse.

The laser-induced damage threshold (LIDT) was measured for a Z n G e P 2 crystal exposed to 0.3-9.5 ps 1030-nm laser pulses. Single-pulse LIDT fluence was ∼0.22J/c m 2 for the laser pulse widths of 0.3-3.5 ps and increased until 0.76J/c m 2 for 9.5-ps pulses. Multi-pulse LIDT fluence for 0.3-ps pulses at repetition frequencies in the range of 100 Hz-1 kHz was ∼0.053J/c m 2 and decreased further at higher, multi-kHz, pulse repetition frequencies. The coating of the Z n G e P 2 crystal surface with an anti-reflection multi-layer thin film increased the multi-pulse LIDT by one order of magnitude, up to 0.62J/c m 2 (about 2T W/c m 2). The significant increase in LIDT coupled with a decrease in reflection losses provides a way to cardinally improve efficiency of frequency conversion of popular 1-µm ultrashort pulses into mid- and far-IR ranges with a thin AR-coated Z n G e P 2 crystal sample.

Broadband (8.5-13.5 µm) intra-pulse difference frequency generation in a LiGaS2 crystal of a 90 fs 744 nm laser pulse after its continuous redshift in air.

Broadband frequency downconversion of a 90 fs 744 nm Ti:sapphire laser pulse into the mid-infrared (IR) was demonstrated via its filamentation-induced self-frequency shift in air and subsequent intra-pulse difference frequency generation in a LiGaS2 crystal. The filamentation of the laser pulse in air provided its continuous spectral broadening to the Stokes wing with spectral humps separated by ∼1000cm-1 that was appropriate for the laser pulse difference frequency conversion into the mid-IR. The difference frequency emission spectrum spanned from 8.5 to 13.5 µm at the e-2 level. The transform limited pulse duration of the mid-IR pulse was 47 fs, which corresponded to a 1.3-cycle laser pulse. Energy conversion efficiency was up to 10-4 and 5⋅10-4 without and with chirp compensation, respectively.

Highly efficient stimulated Raman scattering of sub-picosecond laser pulses in BaWO4 for 10.6 µm difference frequency generation.

Transient stimulated Raman scattering (SRS) of 0.3 ps 515 nm laser pulses in ${\rm BaWO_4}$BaWO4 crystal was experimentally demonstrated with efficiency up to ${\sim}{20}\% $∼20% for the Stokes component with a wavenumber of ${\sim}{925}\;{{\rm cm}^{ - 1}}$∼925cm-1 in a simple single-pass geometry. This anomalous high efficiency was obtained due to the laser pulse self-phase modulation resulting in spectral broadening and seeding the SRS. The applicability of seed pulse production for a high-pressure sub-picosecond ${{\rm CO}_2}$CO2 laser amplifier via difference frequency generation in ${{\rm LiGaS}_2}$LiGaS2 crystal was numerically verified.

Frequency conversion of mid-IR lasers into the long-wavelength domain of 12-20 µm with AgGaSe2, BaGa2GeSe6 and PbIn6Te10 nonlinear crystals.

Difference frequency generation under mixing of repetitively-pulsed CO- and CO2-laser radiation in AgGaSe2, BaGa2GeSe6 and PbIn6Te10 nonlinear crystals was studied. Efficiency and refractive indices were examined for this frequency conversion into the long-wave domain of ∼12-20 µm in the mid-IR. The highest frequency conversion efficiency of 10-4 was obtained for a relatively new PbIn6Te10 crystal, which is an order of magnitude higher than previous results.

Verification of an integral figure of merit for mid-IR nonlinear crystals.

The examination and verification of a simple integral figure of merit for nonlinear crystals, taking into account different crystal properties, was studied. The examination was carried out on the basis of experimental data on the broadband sum frequency generation of CO laser radiation in ZnGeP2, BaGa2GeSe6, AgGaSe2, GaSe, and PbIn6Te10 mid-IR nonlinear crystals. Taking into account spectral and angular phase-matching bandwidths, the figure of merit provides the best agreement with the experiment and can be applied for qualitative, and even quantitative, comparison of the nonlinear crystals.

Three-stage frequency conversion of sub-microsecond multiline CO laser pulse in a single ZnGeP2 crystal.

Broadband three-stage frequency conversion of multiline sub-microsecond CO laser radiation in a single sample of ZnGeP2 crystal was experimentally and numerically studied for the first time, to the best of our knowledge. As a result, the hybrid laser system emitted more than 200 narrow spectral lines within the 2.4-6.2 µm spectral range. The measured conversion efficiencies of the first, second, and third stages were about 4.8%, 0.4%, and 0.05%, respectively. Our numerical simulation demonstrated that the third stage of this frequency conversion can extend the laser system spectrum toward the shorter wavelength of 2.2 µm.

Sum frequency generation of multi-line slab radio frequency discharge carbon monoxide laser system with intracavity nonlinear BaGa2GeSe6 crystal.

A compact repetitively pulsed broadband carbon monoxide (CO) laser system with intracavity frequency conversion, for which a nonlinear crystal was also used as an output coupler, was launched for the first time, to the best of our knowledge. The laser system simultaneously operated in two spectral ranges: CO laser fundamental band (4.9-6.0 µm) and its sum frequencies band (2.45-2.95 µm). Different designs of the laser cavity were considered. Peak powers of the fundamental and sum frequencies laser pulses were up to 2 kW and 10 W, respectively.

Frequency tunable CO laser operating on the highest vibrational transition with wavelength of 8.7 µm.

A carbon monoxide laser emitting on the highest ever observed vibrational transition with a wavelength of 8.7 µm was for the first time launched. An influence of gas mixture content on the CO laser spectrum and factors limiting the longest CO laser wavelength are discussed.

Frequency conversion of molecular gas lasers in PbIn6Te10 crystal within mid-IR range.

PbIn6Te10 is a new mid-infrared (IR) nonlinear crystal with a very wide transparency range from 1.7 up to 31 µm. Calculated phase-matching angles show possibility of frequency conversion throughout the transparency range. Sum frequency generation of multiline carbon monoxide (CO) laser and difference frequency generation when mixing CO and carbon dioxide laser radiation were experimentally studied. Laser-induced damage threshold and frequency conversion efficiency under multiline CO laser pumping were measured.

Broadband two-stage frequency conversion of CO laser in AgGaSe(2) crystal.

For the first time, to the best of our knowledge, a broadband two-stage frequency conversion of multiline CO laser radiation was theoretically and experimentally demonstrated in a single AgGaSe2 crystal. The first stage is sum frequency generation of CO laser radiation. The second stage is concurrent difference frequency generation within 4.3-4.9 µm spectral range when mixing sum frequency radiation with the pump radiation in the same AgGaSe2 crystal. Internal sum frequency generation efficiency of multiline CO laser was up to 1%, while internal difference frequency generation efficiency was up to 0.065%.

Frequency conversion of mode-locked and Q-switched CO laser radiation with efficiency up to 37%.

Frequency conversion of CO laser radiation was experimentally studied in ZnGeP(2) and GaSe nonlinear crystals. To enhance conversion efficiency, we applied a CO laser system "master oscillator power amplifier" with concurrent mode locking and Q switching. The laser system emitted ∼1-µs train of ns pulses. Internal efficiency of frequency doubling reached 37% in ZnGeP(2) crystal and 5% in GaSe crystal. Two-stage frequency conversion (including second-harmonic and difference-frequency generation) in ZnGeP(2) crystal under optical pumping by a selective two-spectral line CO laser was studied.

Cascaded carbon monoxide laser frequency conversion into the 4.3-4.9 µm range in a single ZnGeP2 crystal.

Collinear cascaded mid-IR frequency conversion in a single nonlinear optical crystal was accomplished. Concurrent collinear generation of the sum frequency of multiline fundamental band carbon monoxide laser radiation as a first frequency conversion cascade resulted in collinear difference frequency generation within the 4.3 to 4.9 µm spectral range when mixing this sum frequency radiation with the fundamental one as the second cascade in the same ZnGeP(2) nonlinear optical crystal.