Locking the cavity of a pulsed periodically poled lithium niobate optical parametric oscillator to the wavelength of a continuous-wave injection seeder by an "intensity-dip" method

Injection seeding by a single-mode continuous-wave (cw) laser provides a co nvenient way to achieve narrowband tunable operation of a laser with a broa d spectral gain profile, or of an optical parametric oscillator (OPO). Cont inuous single-mode tunability of the laser or OPO output usually requires t he length of the optical cavity to be controlled as the injection-seeding w avelength is scanned. We report a novel variant on established methods of l ocking the optical cavity length to the seed wavelength. Our approach takes advantage of the resonance properties of an optical cavity. When the cavit y is in resonance with the cw seed radiation, the total intensity of that r adiation reflected off the cavity displays a pronounced dip; this intensity dip can be used as a locking signal to reset the cavity length piezoelectr ically during each interval between the pump pulses that excite the laser o r OPO. Our active cavity-locking scheme is realized in the case of a ring-c avity OPO, incorporating periodically poled lithium niobate (PPLN), pumped at 1.064 mu m by a single-mode pulsed Nd:yttrium-aluminum-garnet laser and injection-seeded at its signal wavelength by a 1.55 mu m single-mode tunabl e diode laser. The coherent infrared output of this injection-seeded PPLN O PO is shown to be continuously tunable, with an optical bandwidth of simila r to 130 MHz (0.0045 cm-1) and excellent spatial beam quality. (C) 1999 Ame rican Institute of Physics. [S0034-6748(99)02808-7].