Miniaturized watt-level laser modules emitting in the yellow-green spectral range for biophotonic applications

Many biophotonic applications used in ophthalmology, dermatology, or flow cytometry rely on laser sources emitting in the yellow-green spectral range. To enable miniaturized laser sources one has to rely on diode lasers. As no direct emitting diode lasers with excellent beam qualities are readily available in this wavelength range, second harmonic generation (SHG) of novel diode lasers emitting wavelengths of 1120 nm and 1152 nm is one feasible approach. For high SHG conversion efficiencies a high beam quality as well as a high optical output power of the fundamental laser light is needed. Our approach is a hybrid integrated master oscillator power amplifier (MOPA) setup which incorporates an optical micro-isolator to protect the MO against back reflections and thereby keep high mode stability. Using individually designed and machined parts based on the results of optical simulations, a platform to integrate different laser system setups has been realized. Using this platform, we were able to compare different approaches of SHG (using planar waveguide or volume LiNbO₃ crystals) and beam output possibilities (free space or fiber-coupled) to satisfy a wide range of applications. In this work we show novel miniaturized diode laser modules emitting more than 2 W and 1.6 W at wavelengths of 560 nm and 576 nm, respectively, which can be used in a wide range of biophotonic applications.