Gregory D. Miller

42%-efficient single-pass cw second-harmonic generation in periodically poled lithium niobate

We present a full-wafer fabrication process for periodically poled lithium niobate with a 6.5-mum domain period. Samples that were 53 mm long and 0.5 mm thick were obtained with this process for single-pass cw 1064-nm Nd:YAG second-harmonic generation. These samples exhibited 78% of the ideal nonlinear coefficient, had a measured conversion efficiency of 8.5% /W in the low-power limit, and produced 2.7 W of cw 532-nm output with 6.5 W of cw input, which corresponds to 42% power conversion efficiency.

Quasi-phase-matched 1.064-μm-pumped optical parametric oscillator in bulk periodically poled LiNbO 3

We report a quasi-phase-matched optical parametric oscillator, using bulk periodically poled LiNbO(3). The optical parametric oscillator, pumped by a 1.064-microm Q-switched Nd:YAG laser, was temperature tuned over the wavelength range 1.66-2.95 microm. The oscillation threshold of approximately 0.1 mJ was more than a factor of 10 below the damage limit. The LiNbO(3) crystal, fabricated by application of an electric field to a sample with liquid and metal surface electrodes, was 0.5 mm thick with a 5.2-mm interaction length and a quasi-phase-matched period of 31 microm.

Vapor-transport equilibrated near-stoichiometric lithium tantalate for frequency-conversion applications.

Near-stoichiometric lithium tantalate (SLT) crystals were produced from congruent lithium tantalate by a vapor-transport equilibration process. Because of the resultant increase in photoconductivity and reduction in photogalvanism, the crystals showed no observable photorefractive damage at 514.5 nm up to the highest intensity used, 2 MW/cm2. The crystals also exhibited low green-induced infrared absorption, a Curie temperature of 693 degrees C, and a coercive field of 80 V/mm. The SLT samples were periodically poled with an 8-microm-period grating, permitting first-order quasi-phase-matched second-harmonic generation of 532-nm radiation at 43 degrees C. A 17-mm-long sample generated 1.6 W of continuous-wave output power at 532 nm for 50 h. With 150-ns pulses at a 100-kHz repetition rate in the same sample, 5-W average-power, 532-nm radiation was generated for 1000 h. No damage to the crystal and no aging effects were observed during these experiments.

PHYSICAL BASIS OF THE DOMAIN ENGINEERING IN THE BULK FERROELECTRICS

We present a review of our theoretical and experimental investigations of the domain engineering aspects of domain structure development. Particular attention is paid to the processes governing the fabrication of periodic domain patterns.

Regular Ferroelectric Domain Array in Lithium Niobate Crystals for Nonlinear Optic Applications

Abstract We present our experimental investigations of the domain evolution in lithium niobate. Particular attention is paid to the short-pitch and nanoscale domain patterning. We demonstrate the production of domain patterns with period down to 2.6 μ.m in 0.5-mm-thick LiNbO3wafers by backswitched poling using lithographic stripe electrodes and nanoscale domain patterns consisting of strictly oriented arrays of nanodomains (diameter down to 30 nm, density up to 100 μm−2).

Optical properties and ferroelectric engineering of vapor-transport-equilibrated, near-stoichiometric lithium tantalate for frequency conversion

Near-stoichiometric lithium tantalate (SLT) crystals were produced from congruent lithium tantalate by vapor transport equilibration, and several important optical and ferroelectric properties were measured. The effect of vapor transport conditions and surface preparation on reproducible ferroelectric engineering of SLT has been studied. Control of these effects along with dramatic decreases in the sensitivity to photorefractive damage and 532 nm absorption has allowed near-room-temperature generation of 10 W of continuous wave 532 nm radiation by second harmonic generation from 29 W of 1064 nm radiation in a 4 cm long device.

Continuous-wave 532-nm-pumped singly resonant optical parametric oscillator based on periodically poled lithium niobate.

We report a continuous-wave (cw) 532-nm-pumped singly resonant optical parametric oscillator (SRO) based on periodically poled lithium niobate. The pump source is a commercial 5-W cw diode-pumped, multilongitudinal-mode, intracavity-doubled Nd:YVO(4) laser. Using a four-mirror ring SRO cavity and single-pass pumping, we achieved subwatt internal oscillation threshold, 56% quantum efficiency, and output tuning from 917 to 1266 nm.

Visible quasi-phase-matched harmonic generation by electric-field-poled lithium niobate

Laser-based displays and illumination systems are applications which can capitalize on the brightness and efficiency of semiconductor lasers, provided that there is a means for converting their output into the visible spectrum. Semiconductor laser manufacturers can adjust their processes to achieve desired wavelengths in several near-infrared bands; an equally agile conversion technology is needed to permit display and illumination system manufacturers to choose visible wavelengths appropriate to their products. Quasi- phasematched second harmonic generation has the potential to convert high-power semiconductor laser output to the visible with 50% optical-to-optical conversion efficiency in a single-pass bulk configuration, using electric-field-poled lithium niobate. Lithographically- defined electrode structures on the positive or negative polar faces of this crystal are used to control the formation of domains under the influence of electric fields applied using those electrode structures. The quality of the resulting domain patterns not only controls the efficiency of quasi-phasematched second harmonic generation, but also controls the degree of resistance to photorefractive damage. We present a model which is used to identify the optimum electrode duty cycle and applied poling field for domain patterning and compare the predicted domain duty cycle with experimental results. We discuss factors which contribute to inhomogeneous domain pattern quality for samples poled under otherwise ideal conditions and our progress in limiting their influence. Finally, we present optical characterization of a 2.4 mm long 500 micrometers thick sample which produced an average second harmonic power of 1.3 W of 532 nm green from a 9 W average power Q-switched 1064 nm Nd:YAG laser in a loose- focus single-pass configuration.

Domain kinetics in the formation of a periodic domain structure in lithium niobate

The evolution of the domain structure in LiNbO3 with polarization switching in an electric field is investigated experimentally. Special attention is given to the formation processes of a regular domain applicable to nonlinear optical devices. A new method based on the spontaneous backswitching effect is proposed for creating a regular structure with a period of 2.6 µm in LiNbO3 with a thickness of 0.5 mm.

Limitations of high-power visible wavelength periodically poled lithium niobate devices due to green-induced infrared absorption and thermal lensing

As nonlinear optics applications of periodically poled lithium niobate (PPLN) scale toward high average powers at visible wavelengths, absorption and thermal effects limit device performance. In second-harmonic generation (SHG) of 532-nm light using 53-mm length PPLN, self-focusing has been observed to limit the green output power to 2 W, with filamentation and sample failure occurring at 2.7 W. In this paper, we examine green-induced infrared absorption (GRIIRA) and thermal lensing in PPLN for 532-nm powers up to 2W, revealing the necessary improvements in this material that are required for high-power visible wavelength applications.