Efficient blue generation from all-solid-state Q-switched Nd:YAG lasers

Abstract

This thesis describes work carried out at Southampton University that has been directed towards achieving high-power all-solid-state blue sources using two low-gain transitions of Nd:YAG. Diode-end-pumping is used to obtain efficient laser performance. The thesis attempts to tackle some of the obstacles to power scaling Q-switched low-gain lasers that use diode-end-pumping schemes.

A 1319nm Q-switched Nd:YAG laser is described that produces a 17KHz pulse train consisting of 353 watt peak power pulses delivering an average power of 780mW for doubling. Periodically poled lithium niobate (PPLN) is used to double to 659.5nm. A 54% second harmonic conversion efficiency produces 360mW of red average power. Sum frequency mixing of the red and infra-red in a second PPLN sample is achieved with a third order grating. A pulsed blue output (13.7 watts peak) at 439.7nm is achieved with good beam quality and an average power of 35mW.

A technique is described to aid power-scaling of polarised laser sources. Analysis of the quarter wave-plate technique demonstrates that the technique will be highly beneficial in reducing the depolarisation loss in low-gain solid-state lasers. The technique is applied to a 946nm laser and a 1319nm laser. Depolarisation of the 946nm source is reduced from 1.66% to 0.0006% and depolarisation of the 1319nm laser is reduced from 1.2% to 0.015%.

The quarter wave-plate technique is implemented in a high power 946nm laser that is Q-switched for low repetition rates. 0.53mJ is extracted with a 5.3KW peak pulse power at 1 kHz repetition rate. The 946nm output is used to generate 473nm blue light via second harmonic generation in non-critically phase-matched LBO at 329° centigrade. An average power of 370mW is demonstrated with a conversion efficiency of 21% at 4kHz repetition rate.

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