The absolute scale of the second-order nonlinear-optical coefficients of several important nonlinear-optical materials has been obtained with improved accuracy. Second-harmonic generation, parametric fluorescence, and difference-frequency generation measurements have been made at several wavelengths in the near-infrared region. The second-harmonic generation measurement was performed at the fundamental wavelengths of 1.548, 1.533, 1.313, 1.064, and 0.852 µm. The materials measured included congruent LiNbO3,1%MgO:LiNbO3,5%MgO:LiNbO3,LiTaO3,KNbO3,KTiOPO4,KH2PO4, quartz, GaAs, GaP, α-ZnS, CdS, ZnSe, and CdTe. We made the parametric fluorescence measurement to determine the nonlinear-optical coefficients of congruent LiNbO3 and 5%MgO:LiNbO3 at pump wavelengths of 0.532 and 0.488 µm. We made the difference-frequency generation measurement for congruent LiNbO3 at a pump wavelength of 0.532 µm. The second-harmonic generation, parametric fluorescence, and difference-frequency generation measurements yielded consistent data on the nonlinear-optical coefficients of the materials. We found that many of the currently accepted standard values are overestimated because of neglect of the multiple-reflection effect in (nearly) plane-parallel-plate samples. The dispersion of the nonlinear-optical coefficients showed that Miller’s Δ is barely constant over the wavelength range measured and thus that Miller’s rule is not so good as other methods for wavelength scaling of the nonlinear-optical coefficients.

Absolute scale of second-order nonlinear-optical coefficients

Nonlinear Optical Crystals: A Complete Survey

The growth in the uses of lithium niobate for infrared applications has created a need for knowledge of its optical characteristics in the infrared spectral region for the purpose of designing phase-matched or quasi-phase-matched devices. We report measurements of the refractive indices of congruently grown lithium niobate and lithium niobate doped with 5 mol. % magnesium oxide. We use these results to predict the tuning curve of a room-temperature multigrating optical parametric oscillator in each material.

Infrared corrected Sellmeier coefficients for congruently grown lithium niobate and 5 mol. % magnesium oxide–doped lithium niobate

Recently, interest in diode laser-pumped solid-state lasers has increased due to their advantages over flashlamp-pumped solid-state lasers. A historical overview is presented of semiconductor diode-pumped solid-state lasers beginning with work in the early 1960s and continuing through recent work on wavelength extension of these devices by laser operation on new transitions. Modeling of these devices by rate equations to obtain expressions for threshold, slope efficiency, and figures of merit is also given. >

Diode laser-pumped solid-state lasers

The analysis and optimization of complex systems can be reduced to mathematical problems collectively known as combinatorial optimization. Many such problems can be mapped onto ground-state search problems of the Ising model, and various artificial spin systems are now emerging as promising approaches. However, physical Ising machines have suffered from limited numbers of spin-spin couplings because of implementations based on localized spins, resulting in severe scalability problems. We report a 2000-spin network with all-to-all spin-spin couplings. Using a measurement and feedback scheme, we coupled time-multiplexed degenerate optical parametric oscillators to implement maximum cut problems on arbitrary graph topologies with up to 2000 nodes. Our coherent Ising machine outperformed simulated annealing in terms of accuracy and computation time for a 2000-node complete graph.

https://science.sciencemag.org/content/sci/354/6312/603.full.pdf

A coherent Ising machine for 2000-node optimization problems.

56% efficient external-cavity-resonant second-harmonic generation of a diode-laser pumped, CW single-axial-mode Nd:YAG laser is reported. A theory of external doubling with a resonant fundamental is presented and compared to experimental results for three monolithic cavities of nonlinear MgO:LiNbO/sub 3/. The best conversion efficiency was obtained with a 12.5-mm-long monolithic ring cavity doubler, which produced 29.7 mW of CW, single-axial mode 532-nm radiation from an input of 52.5 mW. >

/pdf/efficient-second-harmonic-generation-of-a-diode-laser-pumped-51xol2d362.pdf

Efficient second harmonic generation of a diode-laser-pumped CW Nd:YAG laser using monolithic MgO:LiNbO/sub 3/ external resonant cavities

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.

/pdf/optical-parametric-oscillator-frequency-tuning-and-control-3pma11mzg4.pdf

Optical parametric oscillator frequency tuning and control

We describe a doubly resonant optical parametric oscillator (DRO) pumped with the second harmonic of a narrow-linewidth Nd: YAG laser. The linewidth of the DRO signal was less than 13 kHz, the DRO was shown to generate a phase-locked subharmonic of the pump at degeneracy, and the signal and the idler were shown to be mutually coherent with the pump and to be phase anticorrelated with each other away from degeneracy. The signal–idler heterodyne linewidth was 500 Hz, and pump phase modulation was shown to transfer to the DRO phase at degeneracy.

/pdf/coherence-properties-of-a-doubly-resonant-monolithic-optical-5cjgengep5.pdf

Coherence properties of a doubly resonant monolithic optical parametric oscillator

A lamp-pumped, 13-W cw Nd:YAG ring laser at 1.064 μm is injection locked using a 40-mW single-frequency diode-laser-pumped Nd:YAG laser as the master oscillator. The phase fidelity of the injected slave to the master is measured using an all-optical technique.

/pdf/injection-locking-of-a-13-w-cw-nd-yag-ring-laser-9nq9511eqc.pdf

Injection locking of a 13-W cw Nd:YAG ring laser.

A monolithic doubly resonant optical parametric oscillator (OPO) fabricated from MgO:LiNbO3 was pumped by a cw, frequency-doubled, diode-laser-pumped Nd:YAG laser. The threshold for cw operation was 12 mW, and pump depletions of up to 78% were observed two times above threshold. The total OPO output power was 8.15 mW, with a conversion efficiency for the incident pump of 34% and combined conversion efficiency for the 1064-nm laser light of 14%. The OPO was temperature tuned from 1007 to 1129 nm, operated on a single-axial-mode pair over most of the range, and could be electric field tuned by as much as 38 nm near degeneracy.

/pdf/efficient-single-axial-mode-operation-of-a-monolithic-mgo-1s7d1fx3ie.pdf

C. D. Nabors

Papers

Efficient second harmonic generation of a diode-laser-pumped CW Nd:YAG laser using monolithic MgO:LiNbO/sub 3/ external resonant cavities

Optical parametric oscillator frequency tuning and control

Coherence properties of a doubly resonant monolithic optical parametric oscillator

Injection locking of a 13-W cw Nd:YAG ring laser.

Efficient, single-axial-mode operation of a monolithic MgO:LiNbO 3 optical parametric oscillator