Nonlinear optical frequency conversion of mode-locked all-solid-state lasers
The work contained in this thesis concerns the design, development and implementation of robust diode-pumped solid-state mode-locked lasers as a platform for nonlinear optical frequency conversion experiments. One objective is to create an ultrashort-pulsed source that is tunable between λ = 600nm and λ = 700nm, since currently no other laser gain media exists that covers this region of the electromagnetic spectrum. This novel source is intended for application to multiphoton imaging. The first demonstration of additive pulse mode-locking of a diode-pumped Nd³⁺: YVO₄ laser operating in the near-infrared is presented and the source characteristics compared to a similar system that is mode-locked using a saturable Bragg reflector. Although the additive-pulsed mode-locked laser demonstrates higher peak power, it is observed to be less robust due to vibrational intolerance. Therefore, the saturable Bragg reflector mode-locked laser is chosen as the basis for frequency conversion experiments. This source is used to develop an efficient picosecond-pulsed ultraviolet laser that is intended to pump an optical parametric oscillator to realise tunable visible radiation in the wavelength region of interest. Using a resonant enhancement method to generate the third harmonic of the near-infrared laser, an average power of 320mW at λ = 355nm is measured, with a peak power of approximately 68W. However, experiment and calculation proves this to be insufficient to reach the oscillation threshold of the proposed optical parametric oscillator to realise a visible tunable source. The near-infrared laser is also used to obtain mid-infrared radiation by use of a quasiphase-matched optical parametric oscillator. An average power of 1W tunable from λ =1460-1601nm is achieved. This is mixed with some fundamental radiation in a nonlinear medium to generate radiation that is tunable from λ = 610 to 650nm. This system is presented with emphasis on suitability for multi-photon imaging.