Pulse-to-pulse wavelength tuning of an injection seeded nanosecond optical parametric generator with 10 kHz repetition rate

Abstract.

This paper reports on the pulse-to-pulse wavelength tuning of a multiwatt narrow-linewidth nanosecond optical parametric generator (OPG). The OPG consists of a 55 mm long periodically poled lithium niobate (PPLN) crystal with a domain period of 29.75 μm. Excited by 5.7 W of 1064 nm laser pulses (duration: 10 ns, repetition rate: 10 kHz, spatial beam quality M²=1.2) the OPG generates 1.78 W of signal radiation and 0.79 W of idler radiation. The total output of 2.57 W corresponds to a crystal internal efficiency of 64%. The wavelength and spectral width of the OPG is controlled by injecting the cw single mode radiation of a 1580.2 nm DFB diode laser. A seed power as low as 20 μW is sufficient for complete control of the wavelength and the (90 MHz) linewidth of the OPG output. Fast tuning of the diode laser frequency is possible with a rate of up to 6×10⁷ GHz/s by changing the diode current. This allows pulse-to-pulse wavelength tuning of the 10 kHz OPG over a range of 25 GHz limited only by the maximum variation of the current (of 60 mA) allowed for the DFB diode laser used. Increasing the current from 35 mA to 95 mA changed the diode power from 0.3 mW to 5.7 mW. Since these power levels are well above the required minimum seed power, the change of the diode current changes the wavelength of the OPG, but not its linewidth or its output power.