Deep-ultraviolet picosecond flat-top pulses by chirp-matched sum frequency generation.

Picosecond, flat-top, deep-UV pulses are needed to generate high-brightness electron beams to efficiently drive x-ray free electron lasers. Current metal photocathodes have low efficiency and therefore require high-energy pulses, and the generation of high-energy, flat-top pulses in the deep UV is still challenging. The low efficiencies of both the harmonic generation and deep-UV pulse shapers restrict the accessible pulse energy. Moreover, the acceptance bandwidth of the harmonic generation limits the minimum rise time of the flat-top profile. We present the generation of few-hundred microjoule, picosecond, deep-UV pulses using chirp-matched sum frequency generation. This scheme combined with IR spectral manipulation is a novel approach for deep-UV pulse shaping. It permits flat-top pulses with high energy and fast rise time, highly suited for high-brightness photoelectron beam production.

Phase-preserving chirped-pulse optical parametric amplification to 17.3 fs directly from a Ti:sapphire oscillator.

Phase-stabilized 12-fs, 1-nJ pulses from a commercial Ti:sapphire oscillator are directly amplified in a chirped-pulse optical parametric amplifier and recompressed to yield near-transform-limited 17.3-fs pulses. The amplification process is demonstrated to be phase preserving and leads to 85-microJ, carrier-envelope-offset phase-locked pulses at 1 kHz for 0.9 mJ of pump, corresponding to a single-pass gain of 8.5 x 10(4).

Measurement of the nonlinear coefficient of orientation-patterned GaAs and demonstration of highly efficient second-harmonic generation.

Quasi-phase-matched (QPM) GaAs structures, 0.5 mm thick, 10 mm long, and with 61-mum grating periods, were grown by a combination of molecular-beam epitaxy and hydride vapor phase epitaxy. These were characterized by use of mid-IR second-harmonic generation (SHG) with a ZnGeP(2) (ZGP) optical parametric oscillator as a pump source. The SHG efficiencies of QPM GaAs and QPM LiNbO(3) were directly compared, and a ratio of nonlinear coefficients d(14)(GaAs)/d(33) (LiNbO(3))=5.01+/-0.3 was found at 4.1-mum fundamental wavelength. For input pulse energies as low as 50muJ and approximately 60-ns pulse duration, an internal SHG conversion efficiency of 33% was measured in QPM GaAs.

Efficient conversion from 1 to 2 microm by a KTP-based ring optical parametric oscillator.

Conversion of Q -switched 1.064-microm Nd:YAG laser pulses to the 2-2.2-mu; m region with 46% efficiency is demonstrated with a KTP-based type 2 phase-matched optical parametric oscillator (OPO) with two pairs of walk-off compensating crystals in a ring resonator. With 10 mJ of pump energy, we obtain 2.5 mJ at the 2.06-microm signal and 2.1 mJ at the 2.2-microm idler, with a beam quality of M(2) approximately 1.4 . With a ZnGeP(2) -based OPO pumped by the signal from the KTP OPO we achieved 14% conversion efficiency from 1.064microm to the 3-5-microm range.

Effect of resonator length on a doubly resonant optical parametric oscillator pumped by a multilongitudinal-mode beam.

The resonator length of an optical parametric oscillator (OPO) is normally made a short as possible to minimize the signal-buildup time and maximize the output energy. We have found that, when a doubly resonant OPO is pumped by a multilongitudinal-mode beam, its output energy has a significant maximum when its optical length matches that of the pump source, even if this length is much greater than the shortest possible for the OPO. We have observed this effect in a ZnGeP>(2)-based OPO and reproduced it in numerical simulations.

Optical parametric oscillator with non-ideal mirrors and single- and multi-mode pump beams.

Residual re ections of the idler wave in nominally singly resonant optical parametric oscillators can lead to uctuations in the output because the parametric conversion process is sensitive to the phases of the re ected waves. The energy fluctuations in a pulsed optical parametric oscillator are studied experimentally and numerically for single- or multi-longitudinal mode pump beams. We find that the fluctuations are reduced by a multi-mode pump so this may be preferable when unwanted re ections are present. We also observe that the parametric conversion process leads to serious self-focusing of the pump beam, and this limits the maximum safe pump energy.