High efficient difference frequency generation of tunable visible light in a self-controlled process

Generating the difference frequency of a frequency-doubled, widely tunable Ti:Al₂O₃ laser and a Nd:YAG laser provides tunable laser radiation in the visible spectrum range. The generated wavelength region closes the spectral gap between the fundamental and the second harmonic of the Ti:Sapphire laser. A prototype has being developed with a fully automated wavelength tuning, i.e. the wavelength tuning of the Ti:Sapphire laser, the angel tuning of the nonlinear crystals and the tuning of the temporal delay between the Ti:Sapphire and the Nd:YAG laser operate self-controlled. Design, theoretical modeling and experimental characterization of the system are closely discussed. At a repetition rate of one kilohertz, the frequency-doubled Ti:Sapphire laser provides pulses of approximately 20 ns, a spectral line width of 20 GHz. a nearly diffraction limited beam quality and pulse energies of up to 850 μJ. The tuning range reaches from 340 nm to 510 nm. For the three wave interaction process in a 8 mm long BBO crystal the Ti:Sapphire pulses (pump wave) are mixed with 3.5 mJ pulses of a Nd:YAG laser (signal wave). The generated idler wave has pulse energies of up to 280 μJ and pulse durations of approximately 10 ns in the spectral range between 510 nm and 680 nm. This yields to a conversion efficiency of about 33% and a quantum conversion efficiency of more than 50%. To our knowledge, this clearly exceeds the values that has been obtained with comparable setups so far. Further increase of the efficiency is currently under investigation.