The influence of pump beam spatial modulation on angular divergence and temporal characteristics of subnanosecond gain-switched Ti: Sapphire laser was investigated. It was shown, that the change of Ti: Sapphire refraction index by pump light may result in considerable change of laser characteristics. Spatial modulation with frequencies > 15-20 mm-1 induce scattering in laser crystal and leads to the increase of angular divergence in lasers with flat resonator mirrors and large Fresnel number. At the same time induced scattering produces coupling of light within laser aperture, which can result in synchronous generation of all active volume and reduced laser pulse duration.
We report about the development of two new subnanosecond solid-state laser models for application in dermatology and cosmetics. One model uses subnanosecond Nd: YAG microchip laser as a master oscillator and includes Nd: YAG double- and single-pass amplifiers. At 10 Hz this laser produces more than 600 mJ pulse energy with duration 500 +/- 5 ps. Another model (under development) is gain-switched Ti: Sapphire laser with short cavity. This laser produces 200 mJ, 560 ps pulses at 790 nm and uses standard Q-Switched Nd: YAG laser with nanosecond pulse duration as a pumping sourse.
Subnanosecond Nd: YAG laser with output energy at 1064 nm up to 1.1 J and pulse repetition rate 10 Hz was developed for applications, related to medical skin treatment. Available pulse durations are 400 – 750 ps. Laser includes master oscillator with pulse duration 5.5 ns, stimulated Brillouin scattering (SBS) pulse compressor, and amplifier system. Original multi-pass scheme provide compression using liquid cell with small overall length ~15 - 20 cm.
Overlapping of pump beams during multiple passes along cell leads to several effects, which can produce negative influence on output pulse performance. We develop schemes, where overlapping is eliminated or reduced, and obtain reliable generation of compressed pulses with the same duration and stability, as can be obtained for long (with total length ≥ 70 cm) single-pass SBS compressors.
Two years ago we reported about the development of solid state laser source for medical skin treatment with wavelength
310.6 nm and average power 200 mW. Here we describe the results of investigation of the advanced version of the laser,
which is a more compact device with increased output power and flat top beam profile. Ti: Sapphire laser, the main
module of our source, was modified and optimized such, that UV average power of the device was increased 1.7 times.
Fiber optic homogenizer was replaced by articulated arm with diffraction diffuser, providing round spot with flat profile
at the skin. We investigated and compare characteristics of Ti: Sapphire lasers with volume Bragg grating and with fused
silica transmission grating, which was used first time for Ti: Sapphire laser spectral selection and tuning. Promising
performance of last gratings is demonstrated.
We report about the development of all-solid-state laser source of narrowband UV-B light for medical applications. The device is based on a gain-switched Ti: Sapphire laser with volume Bragg grating, pumped at 532 nm and operating at 931.8 nm, followed by a third harmonic generator and a fiber optic beam homogenizer. The maximum available pulse energy exceeded 5 mJ at 310.6 nm, with a pulse repetition rates of 50 Hz. The output characteristics satisfy the medical requirements for psoriasis and vitiligo treatment. A new optical scheme for third harmonic generation enhancement at moderate levels of input intensities is proposed and investigated. As a result, 40% harmonic efficiency was obtained, when input pulse power was only 300 kW.