Phase-matched Optical Parametric Oscillator Research Articles

Cascaded terahertz-wave generation efficiency in excess of the Manley–Rowe limit using a cavity phase-matched optical parametric oscillator

We describe a scheme for efficient terahertz (THz) generation using a cascaded optical parametric oscillator using a GaP sheet cavity. By choosing an appropriate pump wavelength and cavity design, the cascading process contributes to efficient THz-wave generation, resulting in a high output peak power of 1.8 MW and a high photon conversion efficiency of 1.086 at 3 THz. This exceeds the Manley–Rowe limit, and the method described here is applicable to widely tunable and high-power THz-wave generation using an optically isotropic nonlinear optical material, such as GaAs, InP, ZnTe, or GaP. Our simulated data show that high-power THz sources are possible that are suitable for the realization of nonlinear optical effects at THz frequencies.

A non-critically phase matched KTA optical parametric oscillator intracavity pumped by an actively Q-switched Nd:GYSGG laser with dual signal wavelengths

A non-critically phase matched eye-safe KTA optical parametric oscillator intracavity pumped by a dual-wavelength acousto-optically Q-switched Nd:GYSGG laser is demonstrated. Simultaneous dual signal wavelength at 1525.1nm/1531.2nm can be realized using only one laser crystal and one nonlinear crystal. When the absorbed diode pump power at 808nm is 7.48W, the maximum output power, single pulse energy and peak power are 296mW, 2.96μJ and 6.4kW, respectively. As the signal wavelengths exactly locates at the absorption band of C2H2, such an Nd:GYSGG/KTA eye-safe laser has good application prospects in differential absorption lidar (DIAL) for C2H2 detection and difference frequency generation for terahertz waves at 0.77THz.

Compact Nd:YAlO$_{3}$/RbTiOPO $_{4}$ Based Intra-Cavity Optical Parametric Oscillator Emit at 1.65 and 3.13 μm

An intra-cavity optical parametric oscillator based on RbTiOPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> (RTP) crystal simultaneous output eye-safe light and mid-infrared wavelength light was demonstrated. An laser diode end pumped acousto-optic Q-switched Nd:YAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> laser at 1.08 μm was used as the pump source. At an incident pump power of 8.7 W and a pulse repetition frequency of 20 kHz, total average output power up to 1.12 W (890 mW of signal light at 1.65 μm with and 230 mW of idler light at 3.13 μm) was obtained, with the diode to OPO total output conversion efficiency of 12.9%. The pulse width is about 4.5 ns and spectral linewidth is about 0.5 nm for the signal light. Compare to noncritical phase matching optical parametric oscillator using its isomorph KTP crystal, RTP crystal can extend signal wavelength up to 1.65 μm and absorb less idler wavelength.

Tunable, continuous-wave optical parametric oscillator with more than 1W output power in the orange visible spectrum.

We report on the implementation of an all-solid-state optical parametric oscillator (OPO) laser system, pumped by a fiber laser, and extended by intra-cavity sum frequency generation (SFG) to provide tunable radiation with output powers well beyond 1 W in the visible regime between 605 and 616 nm. We use periodically poled sections for quasi phase-matched OPO and SFG processes, implemented on a single MgO:PPLN crystal. A Pound-Drever-Hall frequency stabilization reduces the laser linewidth to the range of 100 kHz (FWHM), determined by measurements of spectral hole burning in a rare-earth ion doped crystal as well as analysis of side-of-fringe transmission in a low finesse Fabry-Perot resonator.

Generation of 2-$\mu{\rm m}$ Light Based on a Noncritical Phase Matching OPO Technique

We propose an experimental technique for efficient 2- μm light generation based on the intracavity noncritical phase matching optical parametric oscillator (OPO). Intra-cavity pumped by a diode pumped actively Q-switched Nd:YVO4 laser operating at 1.3 μm, we have achieved efficient 2093-nm signal beam emission making full use of noncritical phase matching KTA-OPO. At a diode pump power of 9.8 W and a Q-switching repetition rate of 30 kHz, a signal beam with a spectral linewidth of ~ 1 nm and an average power of 1.01 W have been obtained, giving a diode pump power to signal power conversion efficiency of 10.3%. The short pulse width of ~ 3.4 ns is achieved, which is much shorter than other approaches with Q-switched operation to generate 2-μm laser beams.

SHigh pulse energy and symmetrical far field from an optical parametric oscillator in the red spectral range

Red pulses with >30 mJ energy and &lt;0.6 nm bandwidth have been demonstrated using a type 2 phase matched optical parametric oscillator pumped at 532 nm. A symmetrical signal beam with beam diameter-divergence product of ~3 mm•mrad was obtained by applying KTA and BBO crystals in the same resonator

Zn1-xMgxSe: A PROMISING MATERIAL FOR NON-LINEAR OPTICS

A theoretical analysis of the condition of scalar phase-matched second harmonic generation and optical parametric oscillation (OPO) in single-crystalline samples Zn0.52Mg0.48Se is presented. The calculated range of pumping for second harmonic generation with phase matching is 5.1-13 μm. The tuning range of the optical parametric oscillator based on Zn0.52Mg0.48Se is determined. The combination of active media and nonlinear converter for OPO in the same optical element are proposed.

Sellmeier and thermo-optic dispersion formulas for CsTiOAsO4

CsTiOAsO 4 has been found to be phase-matchable for type-2 second-harmonic generation and sum-frequency generation in the 0.5321–1.5915 μm range at 20.0 °C. The Sellmeier equations that correctly reproduce these experimental data as well as the 90° phase-matched optical parametric oscillator wavelengths in the 0.7337–2.4793 μm range are presented together with the thermo-optic dispersion formula.

High pulse energy and symmetrical far field from an optical parametric oscillator in the red spectral range

Red pulses with &gt;30 mJ energy and &lt; 0.6 nm bandwidth have been demonstrated using a type 2 phase matched optical parametric oscillator pumped at 532 nm. A symmetrical signal beam with beam diameter-divergence product of 3 mm·mrad was obtained by applying KTA and BBO crystals in the same resonator.

Tunable and coherent nanosecond 7.2–12.2 μm mid-infrared generation based on difference frequency mixing in ZnGeP2 crystal

A coherent mid-infrared laser source, which can be tuned from 7.2 μm to 12.2 μm based on the type-II phase-matched difference frequency generation (DFG) in an uncoated ZnGeP2 (ZGP) crystal, is reported. The two pump waves are from a type-II phase-matched dual-wavelength KTP optical parametric oscillator (OPO) of which the signal and idler waves are tuned during 1.85–1.96 μm (extraordinary wave) and 2.5–2.33 μm (ordinary wave), respectively. The maximum energy of the generated mid-infrared laser is 10 μJ at 9.22 μm, corresponding to the peak power of 2.2 kW.

Bright filter-free source of indistinguishable photon pairs

We demonstrate a high-brightness source of pairs of indistinguishable photons based on a type-II phase-matched doubly-resonant optical parametric oscillator operated far below threshold. The cavityenhanced down-conversion output of a PPKTP crystal is coupled into two single-mode fibers with a mode coupling efficiency of 58%. The high degree of indistinguishability between the photons of a pair is demonstrated by a Hong-Ou-Mandel interference visibility of higher than 90% without any filtering at an instantaneous coincidence rate of 450,000 pairs/s per mW of pump power per nm of down-conversion bandwidth. For the degenerate spectral mode with a linewidth of 7 MHz at 795 nm a rate of 70 pairs/(s mW MHz) is estimated, increasing the spectral brightness for indistinguishable photons by two orders of magnitude compared to similar previous sources.

Yellow nanosecond sum-frequency generating optical parametric oscillator using periodically poled LiNbO3

Nanosecond yellow light has been generated through simultaneously phase matched sum-frequency generation and optical parametric oscillation in a periodically poled LiNbO3 crystal. 300 mW of yellow light at a wavelength of 586 nm has been generated from 1.3 W of laser power from a Q-switched Yb:YAG laser operating at 1031 nm. The conversion efficiency of the device is 23%.

Intracavity optical parametric oscillator pumped by an actively Q-switched Nd:YAG laser

A non-critically phase-matched KTiOPO4 optical parametric oscillator (OPO) intracavity pumped by a laser diode end-pumped acousto-optically Q-switchedNd:YAG laser is experimentally demonstrated. The highest average power is obtained at the pulse repetition rate (PRR) of around 15 kHz, which is different from the widely reported Nd:YVO4 laser pumped OPO in which the highest average power is obtained at a very high PRR, e.g. 80 kHz. With an incident laser diode power of 6.93 W and a pulse repetition rate of 15 kHz, an average signal power of 0.72 W is obtained with a peak power of 7.7 kW and an optical-to-optical conversion efficiency of 10.4%.

Theory of backward distributed-feedback optical parametric amplifiers and oscillators

We derive a coupled-wave theory for backward phase-matched optical parametric amplifiers and oscillators in a dielectric modulated nonlinear optical material. Unlike a forward phase-matched distributed-feedback optical parametric oscillator, a backward oscillator of this type can have high-threshold gap modes at Bragg resonance and low-threshold detuned modes. In addition to the structure feedback loop, the internal feedback loop in the counterpropagating waves strongly influences the resonant-mode formation in this oscillator. A backward distributed-feedback optical parametric oscillator also exhibits the mode-dependent oscillation threshold similar to that for a distributed-feedback laser and yet has the additional advantage of wavelength selectivity in a much broader parametric bandwidth.

Unconditional temporal instability and self-pulse structuration in the phase-matched degenerate backward optical parametric oscillator

Stability analysis of the degenerate backward optical parametric oscillator in the phase-matching decay interaction, between a CW-pump and a sub-harmonic counter-propagating signal, proves that the inhomogeneous stationary solutions are always temporally unstable whatever the cavity length and pump power above threshold. The nonlinear dynamics exhibits self-pulse structuration of the backward signal with unlimited amplification and compression. Above a critical pulse steepening, dispersion saturates this singular behavior leading to strongly modulated solitary structures.

Efficient conversion from 1 to 2 µm by a KTP-based ring optical parametric oscillator

Conversion of Q -switched 1.064-microm Nd:YAG laser pulses to the 2-2.2-mu; m region with 46% efficiency is demonstrated with a KTP-based type 2 phase-matched optical parametric oscillator (OPO) with two pairs of walk-off compensating crystals in a ring resonator. With 10 mJ of pump energy, we obtain 2.5 mJ at the 2.06-microm signal and 2.1 mJ at the 2.2-microm idler, with a beam quality of M(2) approximately 1.4 . With a ZnGeP(2) -based OPO pumped by the signal from the KTP OPO we achieved 14% conversion efficiency from 1.064microm to the 3-5-microm range.

Tunable phase-matched optical parametric oscillators based on a cylindrical crystal

The use of cylindrical nonlinear crystals is a good way to extend the angular-tuning capability of optical parametric oscillators. We consider the example of a 1064-nm-pumped KTiOPO4 optical parametric oscillator phase matched in the x–z plane. A 31.5° angular tuning is demonstrated, limited by the spectral range of the mirrors. The measured slope efficiency and threshold energy are compared with the values published for a similar optical parametric oscillator that uses a parallelepipedic crystal. We study the beam quality of the emitted signal. The experiments with a plano–plano cavity point out the spatial-filtering effect due to the short focal length of the cylindrical crystal placed in the cavity. A simple model based on the coupling of the pump and the signal Gaussian beams in the cavity is developed. We then investigate the respective effects of the different experimental parameters on the output beam quality: radius of curvature of the mirrors, cavity length, crystal radius, pump-beam waist size, and spectral-tuning range of the signal beam. These calculations lead to the definition of the optimum configuration associated with a low M2 independent of the emitted wavelength. An experimental demonstration of that solution is given with excellent results: M2<1.5 is obtained, constant over 9° angular tuning.

Theoretical analysis of phase-matched second-harmonic generation and optical parametric oscillation in birefringent semiconductor waveguides

We analyze the phase-matching conditions for second-harmonic generation (SHG) and optical parametric oscillation (OPO) in birefringent nonlinear semiconductor waveguides and apply these results to the model system of ZnGeP2 on a GaP substrate. The analyses and numerical results show that phase matching can be achieved for OPO and SHG for reasonable guide thicknesses throughout much of the infrared, indicating significant potential applications for nonlinear birefringent waveguides. For the fundamental mode of a relatively thick guide the region of phase matching and the phase-matching angles are similar to those in bulk material. However, the waveguide has the added flexibility that phase-matched coupling can occur between the various modes of the guide. For example, the phase-matching region for SHG can be considerably extended by coupling the pump into the guide in the fundamental, m = 0, mode and phase matching to the m = 2 mode of the second harmonic. Significantly, the results indicate, among other things, that ZnGeP2 waveguides with harmonic output in the m = 2 mode can be used for efficient SHG from input radiation in the 9.6-10.6-microm region where bulk efficiencies in this wavelength range are too small to be useful.

QUADRATURE PHASE-SQUEEZING OF PUMP FIELD REFLECTED FROM TRIPLY RESONANT QUASI-PHASE-MATCHED OPTICAL PARAMETRIC OSCILLATOR

A quasi- phase-matched optical parametric oscillator(QPM OPO)consisting of a periodically poled LiNbO3(PPLN) crystal is pumped by an all-solid state single frequency Nd:YVO4 laser. The triple resonance of the pump mode and two subharmonic modes with near- degenerate frequencies are experimentally demonstrated by means of precision temperature control of the crystal. The threshold pump power is only 1.2mW. The quadrature phase noise squeezing of the pump field reflected from the OPO up to 1.1dB is observed at the pump power of 2.8 times of the oscillation threshold. The numerically calculated result is in good agreement with the experimentally measured data.

Cylindrical KTiOPO_4 crystal for enhanced angular tunability of phase-matched optical parametric oscillators

We demonstrate what is to our knowledge the first optical parametric oscillator (OPO) based on a cylindrical phase-matched nonlinear crystal. Experiments are performed with an uncoated KTiOPO(4) crystal cut as a cylinder with a diameter of 21.2 mm and a thickness of 5 mm. We achieve 20.5-internal-degree angular tuning in a 1064-nm-pumped type III OPO, which would correspond to ~36 degrees external angular rotation for a parallelepipedal crystal. The goals of using such a device are to narrow the spectral width of the output and to enhance the spatial quality of the generated beams in widely tunable OPO's.