Noncollinear Phase Matching Research Articles

Noncollinear phase matching and effective nonlinear coefficient calculations for biaxial crystal out of the principal plane

Noncollinear phase matching and effective nonlinear coefficient calculations for biaxial crystal out of the principal plane

Ultra-broadband non-collinear optical parametric oscillators: A reliable source of rapidly tunable femtosecond laser pulses

Non-collinear phase matching in optical parametric oscillators enables unique possibilities ranging from ultra-broadband rapid spectral tuning to intrinsic advantages in power scaling. This work is an overview of this concept adapted to different wavelength ranges.

Widely tunable NCPM-KTA OPO based on non-collinear phase-matching in a four-mirror ring cavity.

Based on non-collinear phase-matching (PM), a new method for widely tunable wavelength was proposed and demonstrated in a four-mirror ring cavity of non-critical phase-matching (NCPM) KTiOAsO4 (KTA) optical parametric oscillator (OPO). Wavelength tuning range of 141 nm from 1535.56 nm to 1676.73 nm was achieved by moving one mirror of ring cavity back and forth. The tuning theory and tuning method of non-collinear PM were analyzed in detail. The output energy and pulse width of signal were measured and compared in collinear and non-collinear PM condition. This method is also applicable to OPOs of other nonlinear crystals based on four-mirror ring cavity.

Highly sensitive multi-stage terahertz parametric upconversion detection based on a KTiOPO4 crystal.

In this Letter, we demonstrate a highly sensitive multi-stage terahertz (THz) wave parametric upconversion detector based on a KTiOPO4 (KTP) crystal pumped by a 1064-nm pulsed-laser (10 ns, 10 Hz). The THz wave was upconverted to near-infrared light in a trapezoidal KTP crystal based on stimulated polariton scattering. The upconversion signal was amplified in two KTP crystals based on non-collinear and collinear phase matching, respectively, to improve detection sensitivity. A rapid-response detection in the THz frequency ranges of 4.26-4.50 THz and 4.80-4.92 THz was achieved. Moreover, a dual-color THz wave generated from THz parametric oscillator using KTP crystal was detected simultaneously based on dual-wavelength upconversion. The minimum detectable energy of 2.35 fJ was realized with a dynamic range of 84 dB at 4.85 THz, which gives a noise equivalent power (NEP) of the order of 21.3 pW/Hz1/2. By changing the phase-matching angle or the wavelength of the pump laser, it is suggested that the detection of the THz frequency band of interest in a wide range from approximately 1 to 14 THz is possible.

Phase-Matching in Nonlinear Crystal-Based Monochromatic Terahertz-Wave Generation

Optically pumped nonlinear frequency down conversion is a proven approach for monochromatic terahertz (THz)-wave generation that provides superior properties such as continuous and wide tunability as well as laser-like linewidth and beam quality. Phase-matching (PM) is an important connection between the pump sources and nonlinear crystals and determines the direction of energy flow (as well as the output power). In past decades, a variety of peculiar PM configurations in the THz region have been invented and are different from the traditional ones in the optical region. We summarize the configurations that have been applied in nonlinear THz-wave generation, which mainly fall in two categories: scalar (collinear) PM and vector PM (including macroscopic noncollinear PM and microscopic vector PM). The development of this technique could relax the matching conditions in a wide range of nonlinear crystals and pump wavelengths and could finally promote the improvement of coherent THz sources.

Development of single-resonant optical parametric oscillator with tunable output from 410 nm to 630 nm

A single-resonant low-threshold type-I β-Ba2BO4 (BBO) optical parametric oscillator (OPO) with tunable output from 410 nm to 630 nm at 5 kHz repetition rate is reported. By taking the noncollinear phase matching method, low-threshold OPO operation could be obtained compared with the configuration of collinear phase matching, and the maximum optical–optical conversion efficiency of 11.8% was achieved at 500 nm wavelength when 0.4 mJ pump pulse energy was applied. When the noncollinearity angle was preset at 1.6°, 4.8°, and 6.3°, a continuously tuning output with a total spectral range of 220 nm was successfully obtained by adjusting the phase matching angle of the BBO crystal.

Conical third harmonic generation from volume nanogratings induced by filamentation of femtosecond pulses in transparent bulk materials

We report on observations of conical third harmonic emission that emerges during supercontinuum generation produced by self-focusing and filamentation of high (20-200 kHz) repetition rate 180 fs, 1035 nm pulses from an amplified Yb:KGW laser in various nonlinear crystals and glasses: YAG, sapphire, YLF, LiF, CaF2, MgF2, LiSAF, fused silica and BK-7 glass. We show that conical third harmonic generation is a phase-matched four-wave mixing process, where noncollinear phase matching is achieved by means of reciprocal lattice vector, inversely proportional to the period of nanograting, which is inscribed by femtosecond filament in the volume of nonlinear material. The existence of a particular period required to phase match conical third harmonic generation was indirectly verified by investigations of periodicity features of high and low spatial frequency laser-induced periodic surface structures, in which matter is reorganized in a similar fashion.

A Wavelength-Agile Eye-Safe Optical Parametric Oscillator Based on an X-Cut KTP Crystal

A novel scheme to realize widely tunable optical parametric oscillator (OPO) based on an x -cut KTP crystal is demonstrated. The tuning range from 1572.5 nm to 1697 nm was enabled by a 1:1 imaging optical system with a variable deflection mirror to couple the 1064-nm laser pulses into the OPO cavity in the noncollinear phase-matching (PM) configuration. Benefitting from varying the pump direction rather than the cavity axis, the OPO cavity was unaffected so that the stability of the output signal energy and beam direction could be maintained, which greatly facilitates subsequent applications. The change of pump threshold, output energy, linewidth and temporal pulse shapes during wavelength tuning were also discussed.

Calculating properties of non-collinear phase matching in two different polarization for KDP crystal

The properties of non-collinear phase-matching (PM) for potassium dihydrogen phosphate (KDP) crystal were calculated. The properties were calculated numerically for type I phase matching and type II-phase matching. The group delay dispersion (GDD) was determined for KDP at different slant angles and different types of phase matching. The slant angles were 0°, 40°, 60°, and 900°. The pumping, signal, and idler wavelengths were 354.7nm, 1064nm, and 532nm respectively. The time delay deepened on the phase-matching angle for three-wave that interact in KDP crystal founded. Ordinary refractive index and extraordinary refractive index discussed, by calculating these indices the birefringence at each wavelength determined. The group delay dispersion and time delay very important factors for optical communication, laser application, and nonlinear optics.

Potassium L-ascorbate monohydrate: a new metal–organic nonlinear optical crystal

Large size single crystals of potassium L-ascorbate monohydrate (KLAM), (KC6H7O6.H2O) are grown using solution growth technique by lowering the temperature at the rate of 0.24 {\deg}C/h, where water was used as solvent. The structure of KLAM was solved by single crystal XRD. KLAM crystallizes in non-centrosymmetric, monoclinic, P21 space group with lattice parameters a = 7.030(5) {\AA}, b = 8.811(5) {\AA}, c = 7.638(5) {\AA} and \b{eta} = 114.891(5){\deg}. The crystal grows with bulky morphology in all three directions having (100), (-100), (-110), (0-1-1), (0-11), (001) and (00-1) prominent faces. TGA and DSC measurements show that KLAM is stable up to 80 {\deg}C. The crystal shows good optical transparency with a lower cut off as low as 297 nm. Second harmonic conversion efficiency measured on powder sample is 3.5 times that of potassium dihydrogen phosphate (KDP). Phase matching (PM) is observed on a plate of the KLAM. Noncollinear phase matching rings are also observed near the PM directions which help to identify the locus of PM directions. Presence of noncollinear SHG rings up to third order suggests large birefringence and nonlinear optical coefficients. Laser damage threshold value of the crystal is found to be 3.07 GW/cm2, at 1064 nm in 100 direction.

Efficient tunable terahertz generation via noncollinear phase matching in the ZnGeP2 crystal

A novel noncollinear phase-matching (PM) scheme was proposed by introducing a small tunable angle between two pump beams to maximize the effective nonlinear coefficient ( d e f f ) in tunable terahertz wave difference frequency generation in the Z n G e P 2 crystal. Compared with the collinear PM condition, the noncollinear geometry transfers the PM angle to be around θ = 90 ∘ for type-II ( o − e → o ) PM to fully use the maximum nonlinear coefficient d 36 , leading to a high conversion efficiency improved by tens of times in theory. Based on the theory of noncollinear PM, the angle-tuning characteristics were calculated and the crystal design was provided for efficient outcoupling. A rigorous theoretical model was built under small-signal approximation to show the affecting factors of noncollinear PM and reveal its superiority compared with collinear PM.

Stray light autocorrelation for the measurement of ultrashort laser pulses

Abstract Ultrashort laser pulses in the femtosecond range are of growing interest in medicine and micro material processing for industrial applications. The most interesting parameter is the pulse duration, which can only be measured by optical autocorrelation methods incorporating an optically nonlinear medium. Established methods mostly use monocrystalline beta barium borate (BBO) in transmission, exhibiting a high nonlinear conversion efficiency. However, this material is brittle, expensive and sophisticated in adjustment due to the necessary non-collinear phase matching. Since fiber-based high energy femtosecond laser systems become more and more achievable, the conversion efficiency of the nonlinear medium should no longer be seen as the restricting factor. Therefore, this research work discusses the suitability of several nonlinear media with differing translucency. Quartz, ammonium dihydrogen phosphate (ADP) and aluminum nitride (AlN) were compared in a standard autocorrelation setup and a novel versatile setup measuring frequency-doubled stray light. Best results were achieved with AlN, which appears to be a suitable and promising alternative material to BBO, reducing the expenses by two to three orders of magnitude.

Theoretical and experimental study on a large energy potassium titanyl phosphate terahertz parametric source

The combination of a Stokes parametric oscillator and a Stokes parametric amplifier is used to generate high-energy terahertz pulses in KTiOPO4 (KTP) crystal at 5.70 THz. The Stokes parametric oscillator generates Stokes pulses first. And then they are amplified in the Stokes parametric amplifier and at the same time, high energy terahertz pulses are generated via stimulated polariton scattering. When the incident Stokes pulse energy is 36.6 mJ and the pump energy is 580.0 mJ, the amplified Stokes energy is 192.1 mJ and the obtained maximum terahertz pulse energy is 17.0 μJ. Compared with the reported terahertz pulse energy obtained by the KTiOPO4 terahertz parametric oscillators or generators, the terahertz pulse energy is greatly enhanced. In addition, considering the large angle non-collinear phase matching, pump beam depletion, terahertz wave surface-emitted structure, Gaussian pulse distribution, we make a theoretical simulation for the Stokes parametric amplifier through the coupled-wave equations. The theoretical results are in agreement with the experimental results on the whole.

Widely tunable eye-safe optical parametric oscillator with noncollinear phase-matching in a ring cavity.

An effective method for wavelength tuning in an optical parametric oscillator (OPO) was proposed using noncollinear phase-matching (PM) in a ring cavity. This method was particularly useful for noncritically phase-matched (NCPM) KTP/KTA OPOs where changing the crystal orientation or working temperature is ineffective. A wide tuning range in the eye-safe band from 1572.9 nm to 1684.2 nm was realized pumped by an Nd:YAG laser at 1.06 μm in an NCPM KTP OPO while the internal noncollinear angle was tuned from 0 to 3.1° or the external angle from 0° to 5.8°, with slight variation of the deflection angle of one cavity mirror. The good beam quality and high spectrum intensity of the narrow-linewidth Nd:YAG laser resulted in 33.3% conversion efficiency for the collinear case and above 11% throughout the tuning range. Such OPOs have many potential applications where tunable eye-safe lasers are required, and the proposed wavelength tuning method can be extended to all kinds of OPOs.

The Investigation on the Beam Spatial Intensity Distributions in the Injection-Seeded Terahertz Parametric Generator

In terahertz (THz) wave parametric sources, the large angle between the pump and terahertz waves (about 65° in LiNbO3 crystal) will affect the spatial intensity distributions. To investigate how the noncollinear phase-matching affects the spatial intensity properties of the pump, Stokes, and THz waves, we take the injection-seeded THz-wave parametric generator (is-TPG) as an example to study the beam spatial intensity properties via the numerical solutions of the coupled-wave equations. The simulated results demonstrate that the pump and Stokes intensities have significant changes along the THz-wave propagation direction. It is the first time that the spatial intensity distributions of the three waves in the THz-wave parametric sources have been studied in theory. In addition, the output intensity distributions of the pump, Stokes, and THz waves are measured in the designed is-TPG. The measured spatial intensity distributions are in coincidence with the simulated results. Investigations on the beam spatial intensity properties provide a potential approach to improve the THz-wave outputs and the pump conversion efficiency for the is-TPG and other THz-wave parametric sources.

Comprehensive analyses of the thermal insensitive noncollinear phase-matching for power scalable parametric amplifications.

Thermal-induced phase-mismatch distortion, which will dramatically deteriorate the efficient energy transfer, has become a critical obstacle to power scaling of optical parametric amplifiers. To ease this efficiency deterioration, the noncollinear optical parametric amplification (OPA) configuration widely employed to achieve broadband phase-matching (PM) may also serve as a promising approach to optimize the temperature acceptance. In this paper, starting from the noncollinear wave-vector equations, a required thermo- and angle-relationship analogous to that of noncollinear broadband PM is firstly inferred. Based on the presented mathematical criterion, we have explored the potential spectral boundaries of this ingenious temperature insensitive OPA scheme. Full-dimensional simulations of two types of typical OPA processes were quantitatively discussed. Compared with traditional collinear PM designs, the presented noncollinear PM configurations show significant common characteristics on improving the temperature acceptance and subsequently the overall amplification efficiency. For a typical high power parametric process of the 532 nm pumped near-IR OPA at 800 nm especially, incredible temperature bandwidth exceeding 8000 °C was obtained while a YCOB (xz plane) crystal is adopted. What is more, it can also be applied to ameliorate the gain-spectrum thermo-instability of OPA.

Angular Schmidt spectrum of entangled photons: Derivation of an exact formula and experimental characterization for noncollinear phase matching

We derive an exact formula for the angular Schmidt spectrum of the orbital angular momentum (OAM)-entangled states produced by parametric down-conversion (PDC). We show that our formula yields true theoretical spectrum without any convergence issue as has been the case with the previously derived formulas. Furthermore, we use this formula to experimentally characterize the angular Schmidt spectrum for non-collinear PDC. We report the measurements of very broad angular Schmidt spectra corresponding to angular Schmidt numbers up to 233, which, to the best of our knowledge, is the highest number reported so far. Our studies can be very important for OAM-based quantum information applications.

Design of High Average Power OPCPA Based on Simultaneous Temperature and Wavelength Insensitive Phase Matching

Optical parametric chirped-pulse amplification (OPCPA) provides an efficient route to push ultrafast pulses toward ultrahigh peak powers. However, in high average power regime, the unavoidable thermal effects in nonlinear crystals will intrinsically destroy the phase-matching (PM) condition, which fundamentally limit average power scaling. Here, we present a theoretical design of high average power OPCPA based on simultaneous temperature and wavelength insensitive PM. By regulating the temperature set for PM as well as the wavelength of interacting waves in lithium triborate crystal, the noncollinear angles for temperature insensitive PM and wavelength insensitive PM will coincide and thus ensures simultaneous temperature and wavelength insensitive PM condition. We investigate the performances of the proposed PM scheme in comparison with traditional wavelength insensitive noncollinear PM. Because of the larger temperature bandwidth, higher average power can be anticipated in OPCPA with the proposed PM scheme. Besides, the large spectral bandwidth also allows the amplification of sub-10 fs pulses in the visible spectral range. The proposed PM scheme will provide a promising approach in generating ultrashort pulses with high peak and average powers.

Non-critically phase-matched second harmonic generation and third order nonlinearity in organic crystal glucuronic acid γ-lactone

The linear, second order, and third order nonlinear optical properties of glucuronic acid γ-lactone single crystals were investigated. The optic axes and principal dielectric axes were identified through optical conoscopy and the principal refractive indices were obtained using the Brewster's angle method. Conic sections were observed which is perceived to be due to spontaneous non-collinear phase matching. The direction of collinear phase matching was determined and the deff evaluated in this direction was 0.71 pm/V. Open and closed aperture Z-scan measurements with femtosecond pulses revealed high third order nonlinearity in the form of self-defocusing, two-photon absorption, as well as saturable absorption.

Broadband optical parametric chirped pulse amplification in K3B6O10Br crystal near 800 nm

Broadband optical parametric chirped pulse amplification (OPCPA) of the K3B6O10Br (KBOB) crystal at a central wavelength of 800 nm has been demonstrated for the first time. Using type-1 non-collinear phase matching, a 52 nm FWHM bandwidth was achieved around 800 nm. The 0.25 mJ signal was amplified to 23.92 mJ at the pump intensity of 2.1 GW cm−2. The energy gain was 95.68. After compression, 15.31 mJ to 31.9 fs pulses were obtained. The results confirm that KBOB crystal is a potential alternative for efficient, broadband OPCPA near 800 nm.