RF intensity modulated mid-IR light source based on dual-frequency optical parametric oscillation.

Laser detection and ranging (Ladar)-radar uses intensity-modulated laser beam for ranging and remote sensing. It has the advantages of high spatial resolution from Ladar and immunity to atmospheric turbulence from radar, since the synthetic wavelength is in the order of meters. Intensity modulated mid-IR laser can extend the Ladar-radar concept to mid-IR spectrum. An intensity modulated mid-IR light source with tunable wavelength and modulation frequency is presented. A dual-frequency 1064 nm laser is used to pump an optical parametric oscillator with magnesium oxide doped periodically-poled lithium niobate crystal (MgO:PPLN) as the nonlinear medium. The beat note frequency of the dual-frequency pump laser can be tuned from 140 to 160 MHz. When the pump power is 13 W, the idler output power at mid-IR is 2.38 W, corresponding to a pump-idler conversion efficiency of 19.4%. The wavelength of the idler light is tuned from 3.1 to 3.8 μm by changing the temperature of the MgO:PPLN crystal. The modulation spectra of the mid-IR light are studied. The frequency stability of the beat note in mid-IR is compared with the one in the pump, which are 4.1 Hz and 3 Hz in 240 second measuring time, respectively.