Picosecond measurements of absorptive and refractive optical nonlinearities in GaP at 532 nm.

Picosecond time-resolved pump-probe and Z-scan measurements are used to investigate the nonlinear refraction and absorption associated with intense picosecond excitation above the indirect band edge of GaP. The pump-probe results reveal both an instantaneous absorption feature, which is consistent with two-photon absorption, and a long-lived feature that is associated with the generation of free carriers by linear indirect absorption. Z scans conducted with pulses of 25- and 95-ps duration indicate that, for these pulse widths, the nonlinear refraction in GaP is dominated by the linear generation of free carriers and that the role of the electronic Kerr effect is negligible.

Photorefractive nonlinearities caused by the Dember space-charge field in undoped CdTe.

The photorefractive nonlinearity associated with the Dember space-charge field between electrons and holes produced by two-photon absorption is unambiguously isolated and studied in undoped CdTe by using a nondegenerate, forward-probing, polarization-sensitive, transient-grating technique with a temporal resolution of <5 ps.

Picosecond separation and measurement of coexisting photorefractive, bound-electronic, and free-carrier grating dynamics in GaAs.

A novel transient-grating geometry, which is nondegenerate, copropagating, phase matched, and polarization sensitive, is used to isolate and measure independently the ultrafast dynamics of multiple coexisting gratings in GaAs:EL2 with a temporal resolution of <5 psec. This technique permits the measurement of the evolution of the photorefractive grating in materials with zinc blende symmetry, where the photorefractive grating is usually obscured by the stronger free-carrier and instantaneous bound-electronic gratings.

Polarization-rotation switch using picosecond pulses in GaAs.

Photorefractive and free-carrier nonlinearities in GaAs transfer energy from a strong picosecond pump, which is linearly polarized at an arbitrary angle to a weak s-polarized probe, into a p-polarized beam propagating in the probe direction. By placing the GaAs between a crossed pair of high-quality polarizers that are set to extinguish the probe in the absence of the pump, an efficient, high-contrast, high-speed optical switch is realized. By varying the pumpprobe ratio, delay, fluence, and polarization, we can maximize the intensity of the p-polarized component.

Picosecond and femtosecond pulse generation near 1000 nm from a frequency-doubled Nd:YAG-pumped cw dye laser.

We report efficient synchronous mode locking of a 532-nm pumped cw dye laser tunable from 840 to 1030 nm, using a styryl compound as the gain medium. Hybrid synchronously pumped, passive mode locking of the laser using the saturable absorber DaQTeC generated 230-fsec pulses near 975 nm.

Picosecond photorefractive effect in BaTiO(3).

We report the observation of photorefractive index gratings written and read out in BaTiO(3) using single pulses of 30-psec duration and fluences of 1 to 15 mJ/cm(2) at a wavelength of 0.532 microm. While the photorefractive gratings are masked during formation by large free-carrier grating, they are clearly seen from 50 psec to many minutes following the peak in the writing beams.

Femtosecond synchronously pumped Pyridine dye lasers.

Optical pulses as short as 103 fsec at 695 nm and 263 fsec at 733 nm have been generated in synchronously pumped hybrid Pyridine 1 and Pyridine 2 cw dye lasers, respectively, both using the saturable absorber 1,1'-diethyl-2,2'-dicarbocyanine iodide (DDI). These results combine with other data from the same linear cavity to give direct femtosecond generation over the spectral range 560-840 nm.

Variable intracavity spectral windowing in a synchronously pumped femtosecond cw dye laser.

An aperture of variable width has been placed within an intracavity prism sequence in a synchronously pumped femtosecond dye laser. This is shown to permit direct control of the output pulse width in the range approximately 100-500 fsec. Wavelength tunability is achieved by translating the aperture transversely.

Picosecond photorefractive beam coupling in GaAs.

We report the first observation to our knowledge of the photorefractive effect on picosecond time scales. Photorefractive beam coupling in GaAs with picosecond, 1.06-microm pulses is observed owing to charge separation between electrons and the ionized defect EL2(+) at low fluences and to separation between free electrons and holes created by two-photon interband absorption for high fluences.

Nonlinear-optical energy regulation by nonlinear refraction and absorption in silicon.

We demonstrate a new silicon picosecond nonlinear-optical energy regulator for 1-microm radiation. The device has a high transmission for low input energies and a low transmission for high input energies and clamps the output at a constant value. We attribute this optical Zener action to nonlinear refraction and absorption induced in the silicon by the intense picosecond pulses.