High repetition rate tunable lasers
Copper vapour laser (CVL) pumped dye lasers offer a source of high power, kilohertz repetition rate, tunable narrow-bandwidth radiation suitable for many spectroscopic applications in the visible and infra-red. Furthermore, the nonlinear frequency conversion of CVL-pumped dye laser radiation extends the wavelength range of these laser sources into the blue and ultra-violet. A series of experimental investigations have been undertaken to gain a physical understanding of the fundamental parameters necessary for the optimization of the CVL-pumping of dye lasers. Issues addressed include the influence of the CVL cavity design, the pump beam polarization and geometry, the dye oscillator cavity design, the choice of grating materials, and the dye flow rate. A model based on the rate equation analysis of the kinetic processes relevant to optical amplification in dye lasers has been developed, and the results have been used to design amplifiers with extraction efficiencies in excess of 45 %. As a result of the aforementioned investigations, three commercially available pulsed dye lasers have been successfully optimized for CVL-pumping for the first time. Once modified, these dye lasers have typically shown conversion efficiencies in excess of 20%, with frequency bandwidths as narrow as 800MHz, and beam qualities approaching the diffraction limit. The theory of second harmonic generation is reviewed, and a suite of corresponding computer models have been developed to form the basis for a coherent experimental investigation of UV generation using the CVL and CVL-pumped dye lasers. CVL SHG has been demonstrated in jS-barium borate (BBO) and lithium triborate (LBO), with SHG efficiencies in excess of 18% realized for the CVL 511nm line in BBO. For the first time, an experimental comparison of spherically and elliptically focused second harmonic generation has been undertaken. Optimized elliptical focusing is found to be up to 30% more efficient than using conventional spherical focusing in agreement with theoretical predictions. The superior divergence and transverse coherence of CVL-pumped dye lasers, in comparison to those of the CVL, is reflected in the SHG efficiencies achieved in BBO, LBO and lithium iodate. Conversion efficiencies approaching 40% have been demonstrated in lithium iodate, with harmonic conversion coefficients approaching 2400mW/W2 realized at low input powers. The Boyd and Kleinman theory of SHG with focused Gaussian beams is found to provide an excellent description of SHG with CVL-pumped dye laser radiation, and accurately predicts the optimum strength of focusing and harmonic conversion coefficient. For the first time, sum frequency mixing (SFM) of the CVL with a dye laser has been demonstrated, and found to provide a potentially efficient source for tunable UV radiation. Finally, the application of CVL-pumped dye lasers to resonant ionization mass spectrometry and tropospheric hydroxyl (OH) radical detection is discussed, and the spectroscopic potential of a frequency doubled CVL-pumped dye is demonstrated by recording the absorption spectrum of OH at 308nm.