Ultrafast optical switching by use of fully phase-matched cascaded second-order nonlinearities in a polarization-gate geometry.

We show that cascaded second-order nonlinear-optical processes can occur in a convenient polarization-gate beam geometry. Our arrangement uses type II phase matching, and both individual second-order processes (upconversion and downconversion) are simultaneously phase matched. This geometry can be applied to efficient ultrafast optical switching. With a beta-barium borate crystal and lightly focused 250-fs, 7.3-microJ pulses, we achieve a switching efficiency of 15% and an on-off ratio of 3 x 10(4) on a pulse-length-limited time scale.

Direct ultrashort-pulse intensity and phase retrieval by frequency-resolved optical gating and a computational neural network.

Ultrashort-laser-pulse retrieval in frequency-resolved optical gating has previously required an iterative algorithm. Here, however, we show that a computational neural network can directly and rapidly recover the intensity and phase of a pulse.

Measurement of the intensity and phase of ultraweak, ultrashort laser pulses.

We show that frequency-resolved optical gating combined with spectral interferometry yields an extremely sensitive and general method for temporal characterization of nearly arbitrarily weak ultrashort pulses even when the reference pulses is not transform limited. We experimentally demonstrate measurement of the full time-dependent intensity and phase of a train of pulses with an average energy of 42 zeptojoules (42 x 10(-21) J), or less than one photon per pulse.

Frequency-resolved optical-gating measurements of ultrashort pulses using surface third-harmonic generation.

We demonstrate what is to our knowledge the first frequency-resolved optical gating (FROG) technique to measure ultrashort pulses from an unamplified Ti:sapphire laser oscillator without direction-of-time ambiguity. This technique utilizes surface third-harmonic generation as the nonlinear-optical effect and, surprisingly, is the most sensitive third-order FROG geometry yet.

Phase and intensity characterization of femtosecond pulses from a chirped-pulse amplifier by frequency-resolved optical gating.

Frequency-resolved optical gating (FROG) measurements were made to characterize pulses from a Ti:sapphire chirped-pulse amplified laser system. By characterizing both the pulse intensity and the phase, the FROG data provided the first direct observation to our knowledge of residual phase distortion in a chirped-pulse amplifier. The FROG technique was also used to measure the regenerative amplifier dispersion and to characterize an amplitude-shaped pulse. The data provide an experimental demonstration of the value of FROG for characterizing complex pulses, including tailored femtosecond pulses for quantum control.

Ultrashort-pulse measurement using noninstantaneous nonlinearities: Raman effects in frequency-resolved optical gating.

Ultrashort-pulse-characterization techniques generally require instantaneously responding media. We show that this is not the case for frequency-resolved optical gating (FROG). We include, as an example, the noninstantaneous Raman response of fused silica, which can cause errors in the retrieved pulse width of as much as 8% for a 25-fs pulse in polarization-gate FROG. We present a modified pulse-retrieval algorithm that deconvolves such slow effects and use it to retrieve pulses of any width. In experiments with 45-fs pulses this algorithm achieved better convergence and yielded a shorter pulse than previous FROG algorithms.

Ultrashort optical waveform measurements using frequency-resolved optical gating.

We measure the intensity and phase of ultrashort pulses from a self-mode-locked Ti:sapphire laser using the recently developed technique of frequency-resolved optical gating. These results represent to our knowledge the shortest complete optical waveform characterization measurements performed to date. We also verify recent theoretical calculations that predict that the main limitation on the pulse duration from these lasers is the presence of uncompensated higher-order dispersion.

Single-shot measurement of the intensity and phase of a femtosecond UV laser pulse with frequency-resolved optical gating.

We extend to the ultraviolet frequency-resolved optical gating a new method for measuring the intensity and phase evolution of an individual ultrashort pulse without assumption. Using frequency-resolved optical gating, we measure a 310-fs, 308-nm pulse, whose phase is approximately cubic in time. We show that this phase distortion probably results from self-phase modulation and amplifier detuning.

Pulse retrieval in frequency-resolved optical gating based on the method of generalized projections.

We use the algorithmic method of generalized projections (GP's) to retrieve the intensity and phase of an ultrashort laser pulse from the experimental trace in frequency-resolved optical gating (FROG). Using simulations, we show that the use of GP's improves significantly the convergence properties of the algorithm over the basic FROG algorithm. In experimental measurements, the GP-based algorithm achieves significantly lower errors than previous algorithms. The use of GP's also permits the inclusion of an arbitrary material response function in the FROG problem.

Two-photon absorption as a limitation to all-optical switching.

Two-photon absorption can place a fundamental limitation on waveguide all-optical switching devices. We have derived a general criterion to describe this limitation that must be satisfied by all materials. As a specific example, we have experimentally evaluated this criterion for a lead-glass fiber.