Construction of a solid-state RGB laser

In this master thesis project, a solid-state red-green-blue (RGB) laser was built. The project consisted of two parts. In the first part, an actively Q-switched diode-pumped solid-state laser was constructed. As laser gain medium, a Nd:YVO4 crystal, which lased at 1064 nm, was used. The Q-switch was a home built electrooptic modulator based on two RTP crystals. The modulator had a shortest rise time of 15 ns. At a pulse repetition frequency of 1000 Hz, a pulse energy of 39 μJ was obtained from the laser. The peak power was 1.1 kW and the pulse length was 25 ns. Imperfect birefringence compensation in the electrooptic modulator is believed to be the limiting factor for the pulse energy. In the second part of this project, three different frequency conversion stages were considered. The purpose of the frequency conversion stages was to convert light at 1064 nm into red, green and blue light. Based on simulations in the software SNLO, one of the stages was chosen for experimental realization. The practical setup consisted of an optical parametric oscillator (OPO), with a periodically poled KTP crystal as nonlinear medium. When pumping this OPO with frequency-doubled light at 532 nm, a signal at 632.0 nm and an idler at 3362 nm were obtained. At a pump energy of 0.5 mJ, the pump depletion was measured to 30 % and the conversion efficiency to 18 %, meaning 0.07 mJ of red energy. After the OPO, a sum frequency generation (SFG) process between the pump and the idler gave blue at 459.3 nm. The blue energy was however low, only 2 μJ. A way of increasing the conversion efficiency of the SFG process would be to achieve a better overlap between the spectrum of the idler and the acceptance bandwidth of the SFG process. Therefore the bandwidth of the idler was indirectly narrowed by using a volume Bragg grating as incoupler to the signal-resonant OPO. The bandwidth of the signal was in this way decreased by 50 % and the idler bandwidth was believed to have decreased by the same fraction. However, the blue output energy did not increase as expected. Final experiments showed that the blue output energy was strongly dependent on the beam quality of the pump at 532 nm; when the beam quality was changed from M = 6 to M = 1.5, the blue output pulse energy increased from 2.4 μJ to 5.0 μJ.