Self-mode-locking through intra-cavity sum-frequency generation.

A new technique for mode-locking is demonstrated based on two lasers sharing one leg for sum-frequency generation. When the two lasers had equal round trip time one will produce bright pulses and the other dark pulses. Both lasers used Nd:YVO4 as the gain material, but operated at different wavelengths, namely 1064 nm and 1342 nm. In the present configuration, sub-250 ps pulses were generated at a repetition rate of 276 MHz with an output power of 70 mW. With appropriate choice of round trip loss at the two wavelengths it was possible to choose which laser was generating the bright pulses.

Intra-cavity dark pulse generation through synchronized sum-frequency mixing.

A Nd:YVO4 laser operating at 1064 nm generating a stable mode-locked train of 10 ps-long dark pulses with a 211 MHz repetition rate is presented. The mode-locking relies on a periodic loss modulation produced by intra-cavity sum-frequency mixing with a synchronous bright-pulse train from a mode-locked femtosecond Yb:KYW laser at 1040 nm. A modulation depth of 90% was achieved for the dark pulses, confirmed by cross-correlation measurements. The ultrafast loss modulation injects power into the Nd:YVO4 laser cavity modes beyond the laser gain bandwidth. At proper laser cavity length, the detuning interaction of these modes with the lasing modes leads to the generation of periodic ultrafast transients at frequencies above 1.5 THz.

Room temperature photon-counting lidar at 3 µm.

A midinfrared single-photon-counting lidar at 3 µm is presented. The 3 µm photons were upconverted to 790 nm in a periodically poled rubidium-doped KTiOPO4 crystal through intracavity mixing inside a 1064 nm Nd:YVO4 laser and detected using a conventional silicon single-photon avalanche detector (SPAD). The lidar system could distinguish 1 mm deep features on a diffusely reflecting target, limited by the SPAD and time-tagging electronics. This technique could easily be extended to longer wavelengths within the transparency of the nonlinear crystal.

Ion-exchanged waveguides in periodically poled Rb-doped KTiOPO4 for efficient second harmonic generation.

An ion-exchange process has been developed for periodically poled Rb-doped KTiOPO4 (RKTP) which warrants high efficiency and low loss channel waveguides. The domain stability was investigated, and it was found that domain gratings with uncharged walls could stand the ion-exchange process without deterioration. 3.1 mW of blue second harmonic light was generated from 74 mW of radiation at 940.2 nm coupled into an 8 µm wide and 7 mm long waveguide, corresponding to a normalized conversion efficiency of 115%/Wcm2. Waveguides in PPRKTP open the possibility for stable operation at high optical powers, as well as generating entangled photons at low optical powers, and enable the investigation of novel nonlinear processes such as counter-propagating interactions in a waveguide format.

High resolution and sensitivity up-conversion mid-infrared photon-counting LIDAR.

A single-photon-counting mid-infrared LIDAR is presented. 2.4 µm mid-infrared photons were up-converted to 737 nm by intra-cavity mixing in a periodically poled rubidium-doped KTiOPO4 crystal inside a Nd:YVO4 laser. The up-converted photons were detected by a Si single-photon avalanche photodiode (SPAD). A temporal resolution of 42 ps and a dark count rate of 500 Hz were achieved, limited by the SPAD and ambient light leakage. It allowed for detection of two targets separated by only a few millimeters. This technique is easily extendable to longer wavelengths, limited primarily by the nonlinear crystal transparency.