Tellurium crystal pumped with ultrafast 10 µm pulses demonstrates a giant nonlinear optical response.

The nonresonant nonlinear optical response of bulk tellurium (Te) is studied using 220 fs 10 µm laser pulses with photon energy roughly three times smaller than the band gap energy. The Kerr nonlinearity is found to be extremely large (n2,eff = 3.0-6.0 × 10-12 cm2/W), nearly 100 times larger than that of GaAs, depending on crystal orientation. Multiphoton absorption is observed at intensities >109 W/cm2 indicating the importance of free carriers to the overall nonlinear optical response. The large values of the nonlinear susceptibilities of Te open up possibilities of designing thin film elements for mid- and long-wavelength infrared nonlinear photonics.

Plasma dynamics near critical density inferred from direct measurements of laser hole boring.

We have used multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, v_{HB}, of the density cavity pushed forward by a train of CO_{2} laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the v_{HB} falls rapidly as the laser pulse intensity falls at the back of the laser pulse train. A heuristic theory is presented that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. The measured values of v_{HB}, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.

Fabrication and characterization of Teflon-bonded periodic GaAs structures for THz generation.

A novel technique for low-temperature bonding of GaAs wafers using an interboundary Teflon film is developed. A fabricated stack of ten 25x25 mm2 diced wafers demonstrated 75% transmission of a 10 microm CO2 laser beam. Modeling of these Teflon-bonded (TB) structures as sequences of Fabry-Perot etalons gives a good agreement with transmission measurements. A 20x20 mm2 quasi-phase matched structure of five wafers pumped by CO2 laser lines generated the narrow-band THz radiation at a wavelength of 343 microm via a difference frequency mixing process.

Optical Kerr switching technique for the production of a picosecond, multiwavelength CO2 laser pulse.

A wavelength-independent method for optical gating, based on the optical Kerr effect, has been demonstrated. Using this method, we produced 100-ps, 10-kW, two-wavelength pulses (10.3 and 10.6 microm) with a signal-to-background ratio contrast of 10(5) by slicing a long CO2 pulse. The capability of gating consecutive pulses separated on a picosecond time scale with this method is also shown.