Picosecond Pulse Generation at 596 nm via Sum-Frequency Mixing with a Gain-Switched, Fiber-Amplified Laser Diode

The fiber amplification of a gain-switched laser diode and subsequent sum-frequency mixing of the signal with the residual emission from the pump diode of the amplifer is presented as a practical and economical source for realizing picosecond pulse emission in the yellow-orange spectral range at variable repetition rates. Specifically, a gain-switched distributed feedback (DFB) picosecond laser diode emitting at 1532 nm is coupled into an Erbium-doped fiber amplifier (EDFA) that is core-pumped by a narrowband, single-mode laser diode at 976 nm. The length of the active fiber is optimized for achieving amplification to several watts of pulsed peak power at 1532 nm, while simultaneously allowing for a significant transmission of the residual pump power after the amplifier. The co-propagating amplified signal pulse at 1532 nm and residual pump at 976 nm provide a convenient geometry for direct fiber coupling into a periodically poled potassium titanyl phosphate (PP-KTP) waveguide for sum-frequency generation (SFG) of picosecond pulses at 596 nm. The variable operation of the seed diode allows for a free-running and triggered configuration over a wide range of repetition rates for 596 nm pulsed emission from 5 to 80 MHz with pulse energies up to 5 pJ at a pulse duration of sub 122 ps.