Phase-matched Optical Parametric Oscillator Research Articles

Numerical analysis of the spatial behaviour of nanosecond optical parametric oscillators of beta-barium borate

We report on a numerical analysis of the temporal and spatial beam properties of nanosecond optical parametric oscillators (OPOs). The analysis is performed for a 355-nm-pumped critically phase-matched OPO of beta-barium borate. The calculations provide detailed information on the dependence of the OPO beam quality (measured by the quality factor M2) on pump energy. An important result is the strong increase of the M2 value for pump energies exceeding 1–2 times the energy at threshold. Furthermore, a temporal analysis of single OPO pulses indicates that the M2 value strongly increases during the first few nanoseconds of the OPO oscillation. This increase is understood by considering the temporal dynamics of the spatial profiles of the OPO signal beam and the depleted pump radiation.

Theoretical analysis of self-phase locking in a type II phase-matched optical parametric oscillator

We analyze a doubly-resonant type II phase-matched optical parametric oscillator that includes an intracavity waveplate for inducing mutual injection locking between the signal and the idler. The intracavity waveplate provides a linear coupling between the normally orthogonally polarized signal and idler fields and allows for mode locking at frequency degeneracy. Under mode locked conditions the signal–idler phase difference is locked and the optical parametric oscillator becomes self-phase locked. The signal–idler phase can be adjusted by changing the operating point within the locking range. Two self-phase locked modes with different thresholds and signal–idler phases are possible. Characteristics of the self-phase locked regime are presented for different linear coupling strengths.

Observation of two distinct phase states in a self-phase-locked type II phase-matched optical parametric oscillator

We demonstrate self-phase locking in a type II phase-matched optical parametric oscillator by mutual injection locking. An intracavity quarter-wave plate provides polarization mixing between the orthogonally polarized signal and idler that induces signal-idler self-phase locking when their frequency difference is within the capture range. We observed two distinct phase states that differ in their oscillator thresholds and their signal-idler phase differences, in good agreement with theory.

A simultaneously phase-matched tandem optical parametric oscillator

We report the theoretical analysis of a simultaneously phase-matched tandem optical parametric oscillator (STOPO) in which the principal OPO generates a signal which pumps a secondary OPO. Both OPO interactions are assumed to be phase-matched in a single crystal. The cavity has high Q for the signal produced by the principal OPO and has lower Q for the signal of the secondary OPO. The pump and the two idler frequencies are not resonated. The five waves undergoing nonlinear mixing are assumed to be nondegenerate in either frequency or polarization. We show that the useful output, consisting of the two idlers and the signal of the secondary OPO, can be produced with high efficiency over a large dynamic range in the pump intensity. We discuss the tuning with temperature and grating period of a STOPO based on periodically poled LiNbO/sub 3/ pumped at 1.064 /spl mu/m. We present results based on both plane-wave modeling and modeling in three spatial dimensions.

Twin-beam generation in a triply resonant dual-cavity optical parametric oscillator

We demonstrate a low-threshold twin-beam generator using a cw triply resonant optical parametric oscillator consisting of two coupled cavities: one that resonates the signal and idler waves and the other the pump field. An intensity correlation of 5.5 dB was observed at 3 MHz for a type-II phase-matched KTP optical parametric oscillator.

High-efficiency and low-threshold operation of the pump reflection configuration in the noncollinear phase matching optical parametric oscillator

We report on high-efficiency and low-threshold operation of the pump reflection configuration using an additional mirror in the noncollinear phase matching optical parametric oscillator (OPO). Beta-barium borate (β-BBO) cut for type I phase matching is pumped by the second harmonics of a Q-switched Nd:YAG laser. The maximum output efficiency of 22.9% with a slope efficiency of 26.9% was obtained at the wavelength of 756 nm. The threshold energy of 4.9 mJ was obtained. In this scheme, the linewidth was measured to be 1.5 nm.

Phase-matched self-doubling optical parametric oscillator

We report a synchronously pumped intracavity frequency-doubled optical parametric oscillator that employs a single KTiOPO(4) crystal for both parametric generation and frequency doubling. Both nonlinear processes are phase matched for the same direction of propagation in the crystal. The parametric oscillator, pumped by a femtosecond Ti:sapphire laser at a wavelength of 745 nm, generates a green output beam at 540 nm with a 29% power conversion efficiency. Angle tuning in conjunction with pump wavelength tuning provides output tunability in the 530-585-nm range.

Characterization and modeling of a noncollinearly phase-matched femtosecond optical parametric oscillator based on KTA and operating to beyond 4 μm

We describe the design and operation of a critically phase-matched femtosecond optical parametric oscillator based on KTA. By employing a small pump-signal noncollinear angle, tuning of the idler to beyond 4 /spl mu/m is achieved using a Ti:sapphire pump laser. A Gaussian-beam model is described which can be used to identify the optimal noncollinear phase-matching geometry. Idler and signal pulses are characterized fully both temporally and spectrally and interferometric autocorrelation data at 3.5 /spl mu/m showing idler pulses of only eight optical cycles duration are presented.

Generation of tunable picosecond pulses by synchronous pumping of a periodically poled lithium niobate optical parametric oscillator

A tunable quasi phase-matched optical parametric oscillator synchronously pumped at 1.047 µm is reported. The signal was tuned from 1.33 to 1.45 µm, corresponding to a calculated idler tuning range of 2.67 – 4.86 µm. Average signal powers of up to 100 mW and pulse durations of 3.2 ps were obtained.

Comparison of Raman and degenerated optical parametric oscillators for a high‐energy and high‐repetition‐rate eye‐safe laser

A high-pressure laminar flow, methane-filled Raman cell has been used for nonlinear conversion of a 100-Hz Nd-YAG laser operating at 1.06 {mu}m to eye-safe radiation at 1.54 {mu}m. The laminar flow is obtained between two concentric cylinders rotating at the same angular velocity. Using a noncritically phase-matched optical parametric oscillator, the same laser source was also converted to 1.57 {mu}m eye-safe radiation. Pump recirculation was used in both cases. Good conversion efficiencies, almost independent of the pulse repetition rate, were obtained with both conversion techniques. {copyright} {ital 1996 Society of Photo{minus}Optical Instrumentation Engineers.}

Highly efficient low-threshold tunable all-solid-state intracavity optical parametric oscillator in the mid infrared

An intracavity critically phase-matched optical parametric oscillator (OPO) was demonstrated with a LiNbO(3) crystal placed inside the resonator of a diode side-pumped Q-switched Nd:YAG laser. The OPO acted as a singly resonating cavity on the signal with a threshold below 10 MW/cm(2). Output energy as high as 640 microJ was observed at the idler wavelength of 3.7 microm, which corresponds to a conversion efficiency of 1.8% from diode light to idler light. Tunability over the wavelength range 3.3-4.15 microm was obtained by rotation of the LiNbO(3) crystal.

Experimental investigation and numerical simulation of the influence of resonator-length detuning on the output power, pulse duration and spectral width of a cw mode-locked picosecond optical parametric oscillator

We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency.

Visible femtosecond pulses by second-harmonic generation of a cw mode-locked KTP optical parametric oscillator

Efficient generation of femtosecond pulses in the wavelength range from 520 to 675 nm by external frequency doubling the signal wave of a non-critically phase-matched picosecond KTP Optical Parametric Oscillator (OPO) in a non-critically phase-matched temperature tuned LiB3O5(LBO) crystal is demonstrated. An average power of the second harmonic as high as 310 mW at 575 nm was generated. In the absence of group velocity mismatch of LBO for a wavelength of the OPO at about 1.3 µm the minimum second-harmonic pulse width was 400 fs at 645 nm.

Generation of tunable narrow-band midinfrared radiation in a type I potassium niobate optical parametric oscillator

We have demonstrated a type I phase-matched KNbO3 optical parametric oscillator (OPO) pumped by the fundamental of a Q-switched Nd:YAG laser. The wavelengths of the OPO’s signal and idler radiation are tuned continuously in the spectral regions of 1.45–2.01 and 2.27–4.0 μm, respectively. With a 7.8-mm-long crystal the energy density at threshold is 65 MW cm−2 for 9-ns-long laser pulses and a transmission of the outcoupling cavity mirror of 10%. At pump pulse energies of 82 mJ (two times above threshold) the OPO generates pulses of up to 6 mJ at the signal wave and 5.4 mJ at the idler wave. This output corresponds to a total conversion efficiency of 14%. The measured spectral width of the signal wave increases from 2.5 nm (at 1.56 μm) to more than 30 nm (at 1.97 μm). Injection seeding with the idler radiation of a 355-nm-pumped narrow-band β-barium borate OPO reduced the spectral width of the KNbO3 OPO output to a single longitudinal mode.

Doubly resonant optical parametric oscillator formed by index matching cavity mirrors directly onto an uncoated LiB_3O_5 crystal

We demonstrate the use of index-matching fluid to contact cavity mirrors directly onto an uncoated LiB(3)O(5) crystal to form a compact, stable resonator for use as an optical parametric oscillator. Specifically, we report on the characteristics of a continuous-wave, doubly resonant, type II phase-matched LiB(3)O(5) optical parametric oscillator formed in this way. Using a single-frequency argon-ion pumping laser operating at 514.5 nm, we measured a pump power threshold of approximately 100 mW and a total external conversion efficiency of approximately 15%. By altering the crystal temperature under noncritical phase matching, we measured coarse frequency tuning over approximately 36 THz, limited only by mirror coating bandwidths. We discuss also the transverse and longitudinal mode properties of the optical parametric oscillator outputs.

Type-II phase-matched KNbO_3 optical parametric oscillator

A Type-II phase-matched KNbO3 optical parametric oscillator (OPO) pumped at 1.064 μm is described. Calculations shown that the full tuning range of 1.4 to 4.2 μm is attainable, that the peak nonlinear drive is achieved near the ϕ =45° plane, and that the walk-off angles for this interaction are a maximum of ~ 3°. The tuning curve in the ϕ = 45° plane was experimentally verified, and the OPO was operated at signal and idler wavelengths of 1.87 and 2.47 μm, respectively. The relative OPO thresholds measured here indicate that the effective nonlinear coefficient for the Type-II interaction is smaller than that of the corresponding Type-I interaction.

Diode-pumped eye-safe laser source exceeding 1% efficiency

We describe an all-solid-state, diode-pumped, eye-safe laser source at 1.61 microm, based on a Nd:YAG laser and a noncritically phase-matched KTP optical parametric oscillator. Total energy conversion efficiencies of the 1.064-microm pump to 1.61-microm signal and 3.1-microm idler approach 50%, with 35% conversion to 1.61 microm alone. This device produces 1.6 mJ at 1.61 microm with a wallplug efficiency of 1.1% and is readily scalable to higher energies. Tunability over 1.6 to 1.54 microm is obtained by rotation of the KTP crystal about its z axis, with 1.54-microm output obtained for propagation along the y axis under noncritical phase matching.

Nonclassical intensity correlation from a type I phase-matched optical parametric oscillator

Signal and idler beams from a type I phase-matched nondegenerate optical parametric oscillator are separated by a Mach-Zehnder interferometer. Broadband nonclassical intensity correlation is observed, in agreement with a theory that includes pump noise. The maximum observed correlation, which occurs at 1.1 MHz, yields a noise level 2.8 dB below the shot noise.

Type II phase matching in a β-barium borate optical parametric oscillator

We report the first demonstration of a type II phase-matched optical parametric oscillator using β-barium borate (BBO) as the nonlinear optical material. The optical parametric oscillator (OPO) is pumped at 354.7 nm and tuning has been demonstrated over 0.48–0.63 μm and 0.81–1.36 μm. The linewidth of the device, without line narrowing elements, is 0.5–3.0 Å, which is dramatically narrower than that of a corresponding type I phase-matched BBO OPO. Experimentally usable conversion efficiencies of 12% have been achieved.