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A description is given of a repetitively pulse source of narrow-band coherent radiation with continuous frequency tuning in the ranges 1.5–1.85 μm and 2.5–3.7 μm, and with energies per pulse up to 8 and 3 mJ, respectively. The source is based on parametric amplification of a weak IR signal from a difference-frequency generator or from a single-mode optical parametric oscillator. This source was used to determine the spectra of IR absorption and of degenerate four-wave mixing, as well as the spectra of excitation of stimulated resonance Raman scattering of light in some molecules under static or supersonic jet conditions.

H2), methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) in a cell under equilibrium conditions and cooled in free jet expansions. For methane at room temperature the detection limit was 2×1012 molecules per cm3 and quantum state, enabling the detection of trace species with a spatial resolution of 1 mm2×30 mm. In an attempt to study transitions in the ν1+ν3 and 2ν2+ν3 combination bands of CO2 or N2O, it was not possible to observe any DFWM signal. Instead a surprisingly strong, backward- and forward-directed emission was found which could not be attributed to the DFWM process. The signal arising from this emission was more than 2 orders of magnitude stronger than the DFWM signals obtained for other molecules. The frequencies of the emitted radiation were found to correlate with the transitions ν1+ν3→ν1 and 2ν2+ν3→2ν2, respectively. Our investigations lead to the conclusion that the emission can be explained by stimulated Raman scattering, resonantly enhanced by transitions to the combination levels ν1+ν3 and 2ν2+ν3. This process seems to suppress the generation of DFWM signals.

The single shot autocorrelator designed to measure the AF of the ultrashort laser pulses in the temporal range of 30 - 200 fs and in spectral range 730 - 820 nm is described.

A tunable KTP optical parametric oscillator (OPO) operating on a single longitudinal mode of its resonator is described. Single mode operation has been achieved by using an intracavity Fabry-Perot etalon in a short-length OPO resonator. The crystal is pumped by the second harmonic of a 10 Hz, Q-switched, injection-seeded Nd:YAG laser. the tuning range observed with a crystal cut at 60 degrees is 0.75 - 0.87 micrometer for the signal beam and 1.83 - 1.37 micrometer for the idler beam. The linewidth of the OPO is 200 MHz (0.0066 cm -1 ), which is very close to the Fourier limit. The total output energy (signal plus idler) was measured to be up to 0.6 mJ per pulse at a pump energy of 10 mJ.

A tunable KTiOPO4 optical parametric oscillator (OPO) operating in a single longitudinal mode of its resonator is described. Single-mode operation has been achieved by use of an intracavity Fabry–Perot etalon in a short-length OPO resonator. The crystal is pumped by the second harmonic of an injection-seeded Nd:YAG laser. The tuning range observed with a crystal cut at 60° is 0.75–0.87 μm for the signal beam and 1.83–1.37 μm for the idler beam. The linewidth of the OPO is approximately 200 MHz (0.0066 cm−1), which is close to the Fourier-transform limit. The total output energy was measured to be as much as 0.6 mJ per pulse.