Passively Q-switched Nd:YAG lasers and their use in UV light generation

Abstract

Recent advances in optoelectronics open up possibilities to realize new kinds of solid state lasers that utilize powerful diode lasers as pump sources. A laser medium has often several appropriate transitions that provide conditions for lasing. Bright pump sources that have recently become available enable building of efficient lasers for wavelengths utilizing such laser transitions that have been unpractical or even totally unattainable. Pulsed lasers are used to create the intensity needed in the nonlinear conversion. With such a laser, focusing of the light beam into the nonlinear crystal is enough to obtain a decent conversion in the range of a few tens of percents. However, this applies to a laser that is designed to produce high enough peak power for the conversion. In this thesis, passive Q-switching is used to develop high peak power laser sources enabling compact and robust lasers. With these laser sources cascaded frequency conversion using nonlinear processes is demonstrated ranging from IR to deep UV wavelengths. In this thesis, passively Q-switched Nd:YAG laser crystal was used in lasers putting out pulses at 946, 1064 and 1123 nm. By second harmonic generation these lasers were used in creating light in the visible wavelength range at 473 and 561 nm. By further conversions to UV the wavelengths of 374, 280 and 236 nm were created. At IR wavelengths, peak powers of 3.7 and 3.2 kW at 946 and 1123 nm were achieved, respectively, while the peak powers for the deep UV lasers were 100 and 120 W at wavelengths of 280 and 236 nm, respectively. Tuning of the pulse properties was studied through adjusting the laser crystal temperature in Q-switched Nd:YAG laser at 1064 nm. A remarkable 90 per cent change in peak power was achieved by heating of the laser mount by 100°C with all the studied lasers.