The applications of laser to the measurements of ultrasoniocs are described. Ultrasonic intensities can be measured by ultrasonic-light diffraction without disturbing ultrasonic fields. This optical method is capable of very precise measurements of an ultrasonic velocity and absorption in a wide frequency range. Studies are reviewed on ultrasonic relaxation, such as molecular vibration, ion association-dissociation relaxation, and critical phenomena of binary mixtures.

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On the basis of the transient mass-spectrum analysis of CO₂ gas dissociation for various input probe powers P_in, plasm alengths l, gas-flow velocities v and discharge currents I_dis, the dissociation rate (1-δ) and dissociation factor ξ of a CO₂ molecule are found to be modified in an open-cycle fast-axial flow (FAF) CO₂ laser amplifier. The effective dissociation constant D_eff related to (1-δ) is found to be corrected as a function of v and input probe irradiance I_in, and the dissociation-rate constant a_d concerned with the dissociation factor ξ is found to be modified to be v-dependent, though these have been regarded as a constant in a sealed-off system. Furthermore, suction rate δ_f due to the difference in the evacuation rate between CO₂ and CO or O₂ is found to be taken into consideration in (1-δ). Corrections for D_eff and α_d are also qualitatively discussed. By using these corrected parameters, the small-signal gain γ₀ is calibrated to explain experimental results satisfactorily.

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Ultra-short infrared pulses were generated from a DNP 1040 dye laser synchronously pumped by a CPM glass laser newly constructed. Short (3-4 ps) pulses of about 100 per shot were obtained from the glass laser, in which a saturable absorber (NDL 112) of 0.5 mm in thickness was set in the center of a linear cavity of 1.0 min length and a glass rod (LHG-8.5^φ, 75^l) was placed between the cell and a coupling mirror. These glass laser pulses pumped synchronously the dye laser, the dye cell of which was contacted with the rear mirror and the cavity length was adjusted to be a half of the pump laser. The pulse width of the infrared dye laser of weak intensi-ty was measured by an optical Kerr shutter method with a CS₂ cell and the glass laser. The pulse width of a transmitted signal was 3.0 ps including the responce time of the Kerr shutter and the gate pulse width in convolution. The attainable pulse width of this dye laser is estimated to be ab-out 1.0 ps or less for the Gaussian pulse profile by deconvolution.

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Sub-ps pulse generation by an absorber-amplifier system was demonstrated. A new scheme two-step pulse shaping was used to improve the compression ratio and stability. A uv saturable dye, acridine, having a low saturation energy and a low residual absorption was found to be suit-able for strong pulse shortening. We have obtained 400fs pulses with an output energy of 20mJ including ASE less than 0.1%.

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