R. C. Eckardt

Quasi-phase-matched optical parametric oscillators in bulk periodically poled LiNbO 3

We review progress in quasi-phase-matched optical parametric oscillators in bulk periodically poled LiNbO3. Using the electric-field poling process, we can reliably fabricate 0.5-mm-thick crystals with uniform domain structures over a 15-mm length. Periodically poled material retains the low-loss and bulk power handling properties of single-domain LiNbO3, and quasi phase matching permits noncritical phase matching with d33, the highest-valued nonlinear coefficient. Optical parametric oscillators pumped by 1.064-μm pulsed Nd:YAG lasers have been operated over the wavelength range 1.4–4 μm with tuning by temperature or by quasi-phase-matched period. We have shown an oscillation threshold as low as 0.012 mJ with a Q-switched pump laser and pumping at greater than ten times threshold without damage. We have also demonstrated a cw doubly resonant oscillator near 1.96 μm pumped directly with a commercial cw diode laser at 978 nm.

Absolute and relative nonlinear optical coefficients of KDP, KD*P, BaB/sub 2/O/sub 4/, LiIO/sub 3/, MgO:LiNbO/sub 3/, and KTP measured by phase-matched second-harmonic generation

Both absolute and relative nonlinear optical coefficients of six nonlinear materials measured by second-harmonic generation are discussed. A single-mode, injection-seeded, Q-switched Nd:YAG laser with spatially filtered output was used to generate the 1.064- mu m fundamental radiation. The following results were obtained: d/sub 36/(KD*P)=0.38 pm/V, d/sub 36/(KD*P)=0.37 pm/V, mod d/sub 22/(BaB/sub 2/O/sub 4/) mod =2.2 pm/V, d/sub 31/(LiIO/sub 3/)=-4.1 pm/V, d/sub 31/(5%MgO:MgO LiNbO/sub 3/)=-4.7 pm/V, and d/sub eff/(KTP)=3.2 pm/V. The accuracy of these measurements is estimated to be better than 10%. >

Second harmonic generation and accurate index of refraction measurements in flux-grown KTiOPO 4

Accurate index of refraction measurements have been performed in flux-grown KTiOPO(4). These measurements give good agreement between experiment and theory for angle phase matching in Type II second harmonic generation at 1.064 microm. These refractive-index data have allowed us to calculate the propagation angles for second harmonic generation at wavelengths of interest other than 1.064 microm such as 1.34 microm. Type II second harmonic energy conversion efficiency of 1.064 micro m of up to 59% in this material has also been demonstrated with higher efficiencies possible. Limits to conversion efficiency are discussed.

Multigrating quasi-phase-matched optical parametric oscillator in periodically poled LiNbO 3

We report a widely tunable quasi-phase-matched optical parametric oscillator that uses periodically poled LiNbO(3)with a multigrating structure. The device is tuned by translation of the crystal through the resonator and pump beam, with no realignment needed. With a 1.064-microm acousto-optically Q-switched Nd:YAG pumplaser, we produced noncritically phase-matched tunable IR output from 1.36 to 4.83 microm. The threshold was 6 microJ for a 26-mm interaction length. The extraordinary polarization of LiNbO(3) has better IR transmission than does the ordinary polarization, permitting operation at longer wavelengths with d(33) quasi-phase matching than with conventional Type I birefringent phase matching.

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.

AgGaS2 infrared parametric oscillator

We report the first operation of an optical parametric oscillator in a chalcopyrite crystal, AgGaS2. Tuning from 1.4 to 4.0 μm is demonstrated for 1.06‐μm Nd:yttrium aluminum garnet pumping. The potential tuning range extends to the 12‐μm transparency limit of the crystal.

Visible BaB2O4 optical parametric oscillator pumped at 355 nm by a single-axial-mode pulsed source

A visible BaB2O4 optical parametric oscillator (OPO) pumped by a single‐axial‐mode 355‐nm source has been demonstrated. An average output power of 140 mW with a signal wave conversion efficiency of 13% and an idler conversion efficiency of 11% for a total conversion efficiency of 24% has been achieved. The oscillator has continuously tuned from 412 nm to 2.55 μm limited by the infrared transmission range of the crystal. Through injection seeding we obtained single‐axial‐mode OPO operation with a corresponding OPO linewidth of less than 3 GHz.

Optical parametric oscillator frequency tuning and control

The frequency-tuning and -control properties of monolithic doubly resonant optical parametric oscillators are analyzed for stable single-mode pump radiation. Single-axial-mode operation is observed on the idler and the signal for both pulsed and continuous pumping. Projections are made for tuning-parameter tolerances that are required for maintenance of stable single-frequency oscillation. Continuous frequency tuning is possible through the simultaneous adjustment of two or three parameters; thus the synthesis of specific frequencies within the broad tuning range of the doubly resonant optical parametric oscillator is permitted.

Broadly tunable infrared parametric oscillator using AgGaSe2

The first successful operation of a AgGaSe2 infrared parametric oscillator is reported. Continuous tuning ranges of 1.6–1.7 μm, 6.7–6.9 μm, and 2.65–9.02 μm were achieved using 1.34‐μm neodymium and 2.05‐μm holmium pump lasers. Pulse energies exceeding 3 mJ, peak powers near 100 kW, and conversion efficiencies of 18% were obtained. Operation of the parametric oscillator was possible well below the 13–40 MW/cm2 surface damage threshold of this nonlinear material.

Phase matching limitations of high efficiency second harmonic generation

-A discussion of second harmonic generation with imperfect phase matching in the high conversion limit is presented. Phase modulation of the fundamental pulse, dispersion, central frequency wavevector mismatch, and fundamental depletion are included. The results show that even small amounts of phase modulation or central frequency wavevector mismatch can limit harmonic generation and must be considered at high conversion efficiency. Both spatial and temporal phase matching parameters are more restrictive at high conversion efficiency because of the narrowing of the central phase matching peak. If the harmonic conversion process is overdriven, severe distortion of the harmonic and transmitted fundamental pulses can result. Cascade harmonic generation of neodymium laser radiation to 266 nm is presented as an example.