Tailored UV-laser source for fluorescence spectroscopy of biomolecules

A dual-wavelength UV-laser source was developed for biosensing. First, a passively Q-switched diode-pumped Nd:YAG laser was constructed. The astigmatic diode output beam was converted into a homogenous beam profile by utilizing a mode converter. As a result, a frequency-doubling conversion efficiency of 50% was achieved in a periodically poled KTiOPO4. With a repetition rate of 100 Hz, the pulse energies and lengths were 650 μJ and 1.8 ns, respectively, at 532 nm with a M2 of 1.3. The UV-generation is based on cascaded parametric processes using an intra-cavity sum-frequency mixing scheme in a periodically poled KTiOPO4 parametric oscillator pumped at 532 nm. Here, the wavelengths 293 and 343 nm were generated, with conversion efficiencies of 7% and 6.5%, respectively, in respect to 532 nm. With pulse length 1 ns and an average power above 2.7 mW, the wavelengths were used for fluorescence measurements of non-pathogenic bacteria.