Avalanche-like behavior of up-conversion luminescence by nonlinear coupling of pumping rates.

Here we report and discuss the avalanche-like up-conversion behavior in absence of the avalanche. We experimentally observed significant changes in the slope of the curve for the intensity dependence of up-conversion luminescence of erbium ions in the green band (520-560 nm) on the pump intensity of the diode laser. Such changes are typical for the photon avalanche. However, the concentration of erbium ions is insufficient for an efficient exchange of energy between them, and the excitation of a photon avalanche is not possible. Using a simple three-level approximation of the up-conversion process model, we have shown that the observed avalanche-like luminescence process can also occur in the absence of a photon avalanche due to the nonlinear relation between the efficiency of two pumping channels of erbium ions caused by the intensity dependence of the pump spectrum.

Low-threshold cavitation in water using IR laser pulse trains.

The low-temperature cavitational disruption by trains of laser pulses was demonstrated in water. The trains used in the experiment were generated by a Raman laser at a wavelength of 1626 nm. The mean value of the fragmentation threshold energy density per pulse in a train was estimated to be equal to 7.2x10(6) J/m(3). The corresponding amplitude of the negative pressure had the order of 6-7 bars at a temperature jump of only about 2 degrees C. This result opens up prospects for developing precision nonthermal cavitational laser surgery.

Continuous-wave Raman generation in a diode-pumped Nd3+:KGd(WO4)2 laser.

Continuous-wave Raman generation in a compact solid-state laser system pumped by a multimode diode laser is demonstrated. The Stokes radiation of stimulated Raman scattering at 1.181 microm is generated as a result of self-frequency conversion of the 1.067 microm laser radiation in Nd3+:KGd(WO4)2 crystal placed in the cavity. The Raman threshold was measured at 1.15 W of laser diode power. The highest output power obtained at the Stokes wavelength was 54 mW. The anomalous delay of Raman generation relative to the start of laser generation (the oscillation buildup) due to slow accumulation of Stokes photons in the cavity at low Raman gain and Raman threshold dependence not only on the laser intensity but also on the time of laser action are observed.

Multimode pumped continuous-wave solid-state Raman laser.

We demonstrate the continuous-wave operation of a solid-state Raman laser containing a barium nitrate crystal as the Raman medium. The Raman laser, which has a singly resonant cavity, is pumped by multimode radiation. The Raman oscillation threshold is reached at approximately 2 W of pump power. As much as 500 kW/cm2 of Stokes power density at 60-kW/cm2 pump power density is obtained in the cavity.

Observation of Raman conversion for 70-fs pulses in KGd(WO4)2 crystal in the regime of impulsive stimulated Raman scattering.

Raman conversion of femtosecond pulses in a solid-state medium is reported. Stimulated Raman scattering (SRS) was observed in an impulsive SRS regime when the pump pulse's duration was comparable with the period of Raman-active vibration. The generation of super broadband radiation, which is a distinguishing feature of impulsive SRS, is shown.