Peter E. Powers

Ti:sapphire-pumped high repetition rate femtosecond optical parametric oscillator

A broadly tunable femtosecond optical parametric oscillator (OPO) based on KTiOPO(4) that is externally pumped by a self-mode-locked Ti:sapphire laser is described. Continuous tuning is demonstrated from 1.22 to 1.37 microm in the signal branch and from 1.82 to 2.15 microm in the idler branch by using one set of OPO optics. The potential tuning range of the OPO is from 1.0 to 2.75 microm and requires three sets of mirrors and two crystals. Without prisms in the OPO cavity, 340 mW (475 mW) of chirped-pulse power is generated in the signal (idler) branch for 2.5 W of pump power. The total conversion efficiency as measured by the pump depletion is 55%. With prisms in the cavity, pulses of 135 fs are generated, which can be shortened to 75 fs by increasing the output coupling.

Recent advances of the Ti:sapphire-pumped high-repetition-rate femtosecond optical parametric oscillator

The details concerning the resonator configuration, crystal parameters, and operating characteristics of high-repetition-rate and high-average-power broadly tunable femtosecond optical parametric oscillators are reviewed and discussed in some detail. We also report new results on an intracavity-doubled optical parametric oscillator with tunability from 580 to 657 nm in the visible and the first, to our knowledge, high-repetition-rate femtosecond optical parametric oscillator with the new nonlinear-optical crystal In:KTiOAsO4, which can potentially tune to 5.3 μm.

Optical parametric oscillation with KTiOAsO4

We present what is to our knowledge the first demonstration of a femtosecond optical parametric oscillator using the new nonlinear crystal KTiOAsO4 Powers of as much as 75 mW in the signal branch and as much as 100 mW in the idler branch were coupled out of the cavity. Pulse widths as short as 85 fs in the signal branch and 150 fs in the idler branch were measured. The potential of tuning out to ~5 μm in the idler branch is discussed.

Electro-optic spectral tuning in a continuous-wave, asymmetric-duty-cycle, periodically poled LiNbO(3) optical parametric oscillator.

We demonstrate electro-optic spectral tuning in a continuous-wave periodically poled LiNbO(3) (PPLN) optical parametric oscillator (OPO). We achieve 8.91 cm(-1) of rapid spectral tuning, with a linear tuning rate of 2.89 cm(-1) /(kV/mm), by applying electric fields up to +/-1.5 kV/mm across the crystal while it is operating within the OPO. Intentionally poling the PPLN crystal with an asymmetric domain structure enables tuning, and numerical predictions closely match the experimental observations. The tuning is considerably larger than the typical operational bandwidth of the OPO, indicating that we are in fact shifting the gain curve of the PPLN crystal.

Periodically poled lithium niobate monolithic nanosecond optical parametric oscillators and generators

We fabricated and characterized periodically poled lithium niobate monolithic optical parametric oscillators (OPOs) and generators. The compact monolithic devices were trivial to align and operate and provided widely tunable, nearly diffraction-limited, stable output pulses. Low thresholds and high conversion efficiencies were obtained when the devices were pumped with 3.5-ns 1.064-mum pulses. In addition, the monolithic OPO devices exhibited broad tuning by crystal rotation through noncollinear phase matching. The bandwidth-broadening effects exhibited in the noncollinear phase-matching geometry were measured and explained.

High-repetition-rate femtosecond optical parametric oscillator based on CsTiOAsO 4

A high-repetition-rate Ti:sapphire-pumped optical parametric oscillator based on the new nonlinear optical crystal CsTiOAsO(4) is described. The operation of this optical parametric oscillator is characterized for a 90 degrees -cut crystal by use of a type II interaction. Tuning from 1.46 to 1.74 microm is demonstrated, and there is the potential for tuning from 0.9 to 5 microm with angle tuning. Powers of 100 mW in the signal and the idler branches are obtained. Pulse widths as short as 64 fs are generated with and without prisms in the cavity.

Periodically poled lithium niobate optical parametric amplifier seeded with the narrow-band filtered output of an optical parametric generator

The results of a simple scheme to generate continuously tunable pulsed narrow-bandwidth (less than 0.1 cm (-1)) light in the infrared are presented. A periodically poled lithium niobate (PPLN) optical parametric amplifier is seeded with the filtered output of a PPLN optical parametric generator. A high-finesse Fabry-Perot etalon is used as the filtering element, giving bandwidths as narrow as 0.08 cm (-1) and tunable over 18 cm (-1) without any adjustments to the PPLN crystals. High efficiency is obtained with a 15-ns 1-kHz Nd:YAG laser, giving energies of up to 180 microJ of signal at 1.6 microm and 60 microJ of idler at 3.3 microm .

Broadband mid-infrared generation with two-dimensional quasi-phase-matched structures

We report the use of highly elliptical pump beams to generate broadband, spatially-chirped mid-infrared light in periodically poled lithium niobate (PPLN). We fabricated PPLN crystals with a fan-out grating period varying continuously from 25.5 to 31.2 /spl mu/m across a 15-mm width and pumped them in both optical parametric generator and monolithic optical parametric oscillator configurations with a Q-switched Nd:YAG laser. Although the fan-out grating pattern is typically thought of as a continuously varying 1-D quasiphase-matched (QPM) structure, the elliptical pump beam illuminates the full 2-D structure of the fan. The phase-matching and gain characteristics of the crystals prefer noncollinear optical parametric generator operation for elliptical pump beams; however, collinear operation was achieved with polished plane- parallel crystal endfaces such that the Fresnel reflections set up a low- finesse monolithic cavity in the crystals themselves. The generated signal and idler beams were spatially chirped in the near field and angularly chirped in the far field while covering spectral bands as large as 1250 cm/sup -1/. With a simple modification, this system also offers an easy way to generate broadband optical frequency combs across the signal and idler spectral bands. We also present theoretical and modeling considerations for large-aperture pumped or flood illuminated 2-D QPM structures. The Fourier transform of the spatial variation in the nonlinear coefficient in a crystal generates a 2-D map of available grating vectors in wave vector mismatch space. This method can be used to glean phase-matching information from complicated 2-D structures that would be difficult to analyze using other methods.

High-repetition-rate femtosecond optical parametric oscillator based on RbTiOAsO 4

A high-repetition-rate Ti:sapphire-pumped femtosecond optical parametric oscillator based on the new nonlinear-optical crystal RbTiOAsO(4) is described. Tuning from 1.03 to 1.3 microm in the signal branch and from 2.15 to 3.65 microm in the idler branch with powers as high as 250 mW in the signal and 200 mW in the idler is presented. The possibility of extending the tuning range beyond 3.65 microm is discussed.

Microlaser-pumped periodically poled lithium niobate optical parametric generator–optical parametric amplifier

For what is believed to be the first time, a single-longitudinal-mode passively Q-switched Nd:YAG microlaser is used to pump a narrow-bandwidth periodically poled lithium niobate (PPLN) optical parametric generator-optical parametric amplifier (OPG-OPA). Before amplification in the OPA, the output of the OPG stage was spectrally filtered with an air-spaced etalon, resulting in spectroscopically useful radiation (bandwidth, ~0.05 cm(-1) FWHM) that was tunable in 15-cm(-1) segments anywhere in the signal range 6820-6220 cm(-1) and the idler range 2580-3180 cm(-1). The ability to pump an OPG-OPA with compact, high-repetition-rate, intrinsically narrow-bandwidth microlasers is made possible by the high gain of PPLN. The result is a tunable light source that is well suited for use in portable spectroscopic gas sensors.