Engineered nonlinear material produces low-loss mid-infrared source
Researchers at the Center for Nonlinear Optical Materials (Stanford University; Palo Alto, CA) have reduced the optical loss of a quasi-phase-matched, diffusion-bonded stack of gallium arsenide (GaAs) plates to that of single-crystal GaAs. The stack consisted of 24 alternately rotated GaAs layers with an average layer thickness of 252 µm. The total length of the stack was 6 mm. The layers were fused in a bonding furnace.
The completed third-order quasi-phase-matching device was tested in a laser at the Blackett Laboratory (Imperial College; London, England) consisting of a double-pass zinc germanium phosphide (ZnGeP2) optical parametric generator pumped by a 2.8-µm erbium chromium-doped YSGG laser. The resulting 4.79- and 6.74-µm output in 96-ps pulses produced tunable 15.6- to 17.6-µm radiation after difference-frequency mixing in the GaAs stack. The peak external conversion efficiency was 0.7%, which corresponded to 5% internal quantum conversion efficiency at 16.6 µm. In the tunable wavelength range, the optical loss coefficient of the bonded stack was almost the same as single-crystal GaAs, according to the researchers. The team says that the use of engineered nonlinear optical materials shows promise for developing tunable infrared sources.