Phase-matching Geometry Research Articles

Spatial-Dependent Spectral Response of Acousto-Optic Tunable Filters with Inhomogeneous Acoustic Distribution.

The spectral response of an acousto-optic tunable filter (AOTF) is crucial for an AOTF based spectral imaging system. The acousto-optic (AO) interaction within the spatial-distributed area of the acoustic field determines the spectral response of the light incidence. Assuming an ideally uniform acoustic field distribution, phase-matching geometries can be applied to calculate the anisotropic Bragg diffraction in AO interactions, determining the wavelength and direction of the diffracted light. In this ideal scenario, the wavelength of the diffracted light depends solely on the direction of the incident light. However, due to the non-ideal nature of the acoustic field, the wavelength of the diffracted light exhibits slight variations with incident position. In this paper, an analytical model is proposed to calculate the spatial-dependent spectral response of the diffracted light under non-uniform acoustic field distribution. The study computes the variation pattern of the diffracted light amplitude caused by the inhomogeneous acoustic distribution. The theoretical considerations and computational model are confirmed by AOTF frequency scanning experiments. The study demonstrates that the distribution of the acoustic field leads to non-uniform spatial-spectral response in the AOTF, and the spatial AO interaction computational model can provide data support for calibrating AOTF systems in imaging applications.

Raman parametric four-wave mixing mechanism of the first-order Stokes generated in CO2 and H2.

Without the axial component, an annular spatial profile of the first-order Stokes (S1) was observed during the SRS process in low-energy pumped CO2 gas, which is supposed to be generated by a parametric four-wave mixing process (PFWM), i.e., 2ωP = ωAS1 + ωS1. In order to verify such a mechanism, similar experiments were conducted in H2, and the annular S1 intensity distribution was also noticed. Furthermore, simulations of S1 radial intensity distributions were carried out based on the proposed PFWM phase matching geometry. The PFWM has been verified to be a process that directly annihilates two pump photons and simultaneously produces one AS1 photon and one S1 photon.

Angular-Spectral Characteristics of Acousto-Optic Tunable Filters Based on Mercurous Halide Crystals.

The angular and spectral properties crucial for the functionality of acousto-optic (AO) devices are determined by phase-matching geometries in AO interactions. In applications such as spectral imagers based on acousto-optic tunable filters (AOTFs), systematic throughput is constrained by the angle separating diffracted and transmitted light. This research introduces an analytical model that elucidates the angular-spectral properties of diffracted beams in mercurous halide crystals. These crystals possess a wide transmissive spectral range, from visible light to long-wave infrared light. The study computes and confirms correlations between the separation angle and parameters including incident angle, polarization, acoustic angle, and crystal birefringence. Experimental validation conducted on mercurous halide and tellurium dioxide crystals demonstrates that higher birefringence in crystals significantly amplifies the separation angle, augmenting the device's performance. The study contributes to the development of devices with large separation angles during the design phase, enhancing systematic throughput in spectral imaging applications.

Acousto-Optic Interaction in Biaxial Crystals

Acousto-optic (AO) interaction in optically biaxial crystals is of great interest due to the variety of phase matching geometries caused by the low symmetry of the acoustic, optical, and photoelastic properties. The current state of the research in the field of acousto-optics of biaxial crystals is presented. Some promising biaxial crystals of the orthorhombic and monoclinic systems, which are of practical interest as materials for AO devices, are considered. The unique geometries of isotropic and anisotropic diffraction that exist in only biaxial crystals are analyzed, and the AO devices based on these crystals are briefly reviewed.

Numerical Investigation of the Temporal Contrast in ps-OPCPA with Compact Double BBO Arrangement

The picosecond optical parametric chirped pulse amplifier (ps-OPCPA) with double BBO arrangement can support the ultrabroad spectrum even under a relatively long pump pulse duration (∼100 ps). In this work, five-wave-coupled equations taking into consideration different phase matching conditions between the parametric superfluorescence (PSF) and the signal are proposed to investigate the temporal contrast in ps-OPCPA schemes. Both the temporal contrast and the amplified spectrum are numerically analyzed in double BBO arrangements with four phase matching conditions. Numerical results show that the high temporal contrast and ultrabroad spectrum can be simultaneously realized by choosing the proper phase matching geometry in a double BBO arrangement. The numerical investigation here relaxes the requirement of very short pump pulses in ps-OPCPA, which can provide beneficial guidance for the design and construction of ps-OPCPA.

Noncollinear phase-matching geometries in ultra-broadband quasi-parametric amplification

Optical parametric chirped pulse amplification (OPCPA) shows great potential in producing ultrashort high-intensity pulses because of its large gain bandwidth. Quasi-parametric chirped pulse amplification (QPCPA) may further extend the bandwidth. However, behavior of QPCPA at a limited pump intensity (e.g., ≤ 5 GW/cm2 in a nanosecond pumped QPCPA) has not yet been investigated fully. We discuss detailedly the ultra-broadband amplification and the noncollinear phase-matching geometry in QPCPA, model and develop a novel noncollinear geometry in QPCPA, namely triple-wavelength phase-matching geometry, which provides two additional phase-matching points around the phase-matching point at the central wavelength. Our analysis demonstrates that the triple-wavelength phase-matching geometry can support stable, ultra-broadband amplification in QPCPA. The numerical simulation results show that ultrashort pulse with a pulse duration of 7.92 fs can be achieved in QPCPA when the pump intensity is limited to 5 GW/cm2, calculated using the nonlinear coefficient of YCa4O(BO3)3.

Noncritical acousto-optic Bragg phase matching: analysis of orthorhombic and monoclinic crystal systems.

Anisotropic acousto-optic diffraction in crystals is the fundamental phenomenon that is used to design acousto-optic tunable filters. Noncritical and quasicollinear phase-matching geometries of Bragg acousto-optic diffraction are compared for acoustic symmetry planes in four crystal systems (tetragonal, trigonal, orthorhombic, and monoclinic). The results for uniaxial crystals are reviewed and generalized for biaxial crystals. It is shown that cubic frequency dependence on the Bragg angle exists in two symmetry planes of orthorhombic crystals and conditionally exists in the symmetry plane of monoclinic crystals. It is also shown that there are two points in the symmetry plane of monoclinic crystals where noncritical phase matching takes place in quasicollinear diffraction geometry that can be used to design high-resolution tunable filters. Phase-matching configurations in α-iodic acid and potassium gadolinium tungstate crystals are analyzed.

Generation of narrowband counterpropagating polarization-entangled photon pairs based on thin-film lithium niobate on insulator

We propose a scheme for the generation of counterpropagating polarization-entangled photon pairs from a periodically poled lithium niobate on insulator waveguide. The waveguide is designed to enable a special dispersion relationship between the T M 00 and T E 00 modes that allows two concurrent counterpropagating quasi-phase-matching type-II spontaneous parametric downconversion processes with a single reciprocal wave vector. Due to the counterpropagating phase-matching geometry, the source has a narrow bandwidth in the order of several gigahertz. The compact source opens up a new method for integrated photonic technologies.

A two-mode squeezed light based on a double-pump phase-matching geometry**Project supported by the National Natural Science Foundation of China (Grant Nos. 11974111, 11474095, 11874152, 11604069, 91536114, 11654005, and 11234003), the Fundamental Research Funds for the Central Universities, China, the Science Foundation of Shanghai, China (Grant No. 17ZR1442800), and the National Key Research and Development Program of China (Grant No. 2016YFA0302001).

We theoretically investigate the frequency-nondegenerate and frequency degenerate squeezed lights with a four-wave mixing process (4WM) driven by two pump fields crossing at a small angle. Different from a 4WM process driven by a single pump field, the refractive index of the corresponding probe field, np, can be converted to a value that is greater than 1 or less than 1 by an angle adjustment. In the new region with np < 1, the bandwidth of the gain is relatively large due to the slow change in the refractive index with the two-photon detuning. In this region with an exchange of the roles of the pump and probe beams, the frequency degenerate and spatial nondegenerate twin beams can be generated, which has potential application in quantum information and quantum metrology.

Theoretical Study of Organic Crystal-Based Terahertz-Wave Difference Frequency Generation and Up-Conversion Detection

Optical pumped quasi-monochromatic and tunable terahertz (THz) wave generation and detection system is investigated theoretically. Calculations are performed on an organic nonlinear medium: 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST), due to the superior properties (large dynamic range and extremely wide tunability). The behavior of pulses during the nonlinear interaction is characterized. Previous experimental results are well explained. Our theoretical model provides an approach to improve the performance of the coherent THz system from two aspects. For the source part, an optimal crystal thickness that maximizes the THz output is obtained. For the detector part, a linear conversion relation (used for calibration) and the parameter dependence of responsivity are provided. It was predicted that a dynamic range of ten orders could be achieved with the DAST-based THz system. The presented model can also be applied to guide the design of THz systems with other nonlinear mediums in collinear phase-matching geometry.

Generation of frequency degenerate twin beams in Rb85 vapor.

We demonstrate a new phase-matching geometry for four-wave mixing processes in hot Rb85 vapor, in which all four fields propagate in different directions but two of them are degenerate in frequency. When used as a parametric amplifier with an injected seed, two types of quantum mechanically correlated twin-beam states, either frequency degenerate or nondegenerate, can be generated. The quantum noise reduction in the intensity difference is almost 7dB for the nondegenerate type and nearly 5dB for the degenerate type. The spatial nondegeneracy of the four waves allows a variety of configurations of parametric processes, leading to flexible control for both phase insensitive and sensitive parametric amplification. The spatially nondegenerate but frequency degenerate four-wave mixing process will find wide applications in quantum metrology, quantum communication, and quantum information of continuous variables.

Electric field measurements in a nanosecond pulse discharge in atmospheric air

The paper presents the results of temporally and spatially resolved electric field measurements in a nanosecond pulse discharge in atmospheric air, sustained between a razor edge high-voltage electrode and a plane grounded electrode covered by a thin dielectric plate. The electric field is measured by picosecond four-wave mixing in a collinear phase-matching geometry, with time resolution of approximately 2 ns, using an absolute calibration provided by measurements of a known electrostatic electric field. The results demonstrate electric field offset on the discharge center plane before the discharge pulse due to surface charge accumulation on the dielectric from the weaker, opposite polarity pre-pulse. During the discharge pulse, the electric field follows the applied voltage until ‘forward’ breakdown occurs, after which the field in the plasma is significantly reduced due to charge separation. When the applied voltage is reduced, the field in the plasma reverses direction and increases again, until the weak ‘reverse’ breakdown occurs, producing a secondary transient reduction in the electric field. After the pulse, the field is gradually reduced on a microsecond time scale, likely due to residual surface charge neutralization by transport of opposite polarity charges from the plasma. Spatially resolved electric field measurements show that the discharge develops as a surface ionization wave. Significant surface charge accumulation on the dielectric surface is detected near the end of the discharge pulse. Spatially resolved measurements of electric field vector components demonstrate that the vertical electric field in the surface ionization wave peaks ahead of the horizontal electric field. Behind the wave, the vertical field remains low, near the detection limit, while the horizontal field is gradually reduced to near the detection limit at the discharge center plane. These results are consistent with time-resolved measurements of electric field components, which also indicate that vertical electric field reverses direction after the ionization wave.

Output features of optical parametric chirped pulse amplification in LiB3O5 near 800 nm at different phase-matching geometries.

We theoretically and experimentally investigated the output beam quality and wavefront distortion in four different phase-matching geometries in LBO-OPCPA at 800 nm: broadband noncollinear geometry, collinear geometry, pump-idler the Poynting vector collinear (Sp∥Si) geometry, and pump-signal Poynting vector collinear (Sp∥Ss) geometry. It was found that the output profile is closely related to the noncollinear angle between Poynting vectors of parametric waves. However, the wavefront evolution depends mainly on the angles between the wave vectors. Broadband noncollinear geometry has the largest spatial modulation and wavefront distortion. Good output beam quality can be achieved in collinear geometry with little wavefront distortion, but the bandwidth is only approximately 10 nm. The Sp∥Ss and Sp∥Si configurations result in a bandwidth of more than 20 nm with enhanced beam quality and small wavefront distortion. The two geometries have different output features wherein the former has a relatively lower modulation, and the latter shows smaller wavefront distortion.

Analysis of parametric fluorescence amplified in a noncollinear optical parametric amplifier pumped by the second harmonic of a femtosecond Yb:KGW laser

We present the results of theoretical and experimental investigation of amplified parametric fluorescence (APF) produced in a high-gain BBO-based femtosecond noncollinear optical parametric amplifier (OPA) pumped at 515 nm. Differences of APF levels in Poynting vector walk-off-compensating and tangential phase-matching amplification geometries are examined. APF suppression due to the presence of a seed pulse in the OPA is measured and is found to be around 6 times in typical OPA operating conditions when pump-to-signal conversion efficiency is 11.5%.

The role of ferroelectric domain wall in nonlinear Cerenkov frequency up-conversion in 1D nonlinear crystal

We reveal a variety of nonlinear Cerenkov radiation (NCR) patterns that occur in a single photonic crystal modulated by domain walls, which manifest themselves as normal, degenerated, and anomalous-dispersion-like NCR type sum-frequency generation. The phase-matching geometries of the evolution of Cerenkov radiation varying with the dispersion relationship among the interaction waves are exploited, respectively.

Second-harmonic generation of focused ultrashort x-ray pulses

We study the process of x-ray second-harmonic generation (SHG) from focused ultrashort pulses. We numerically simulate and derive approximated analytical expressions for the efficiency and tolerances of the SHG process, considering the effects of temporal and spatial walk-off, and the coupling to the linear Bragg scattering. We show that for the recently observed x-ray SHG in diamond, the simultaneous Bragg diffraction of the generated second harmonic is negligible. However, spatiotemporal walk-off effects are crucial components regarding the wave propagation aspects of this process, due to the highly noncollinear phase-matching geometry.

Normal, degenerated, and anomalous-dispersion-like Cerenkov sum-frequency generation in one nonlinear medium

We report on the experimental realization of Cerenkov sum-frequency generation across the material dispersion in a one-dimensional, periodically poled ferroelectric crystal. Three schemes of sum-frequency generation, confined only in the vicinity of domain walls and in the form of nonlinear Cerenkov radiation, are demonstrated in normal, degenerated, and anomalous-dispersion-like configurations. We exploit their phase-matching geometries, which exhibit a whole scenario of the evolution of Cerenkov radiation varying with the dispersion relationship among the interaction waves. In addition, two sets of conical sum-frequency generation with different radius and center are demonstrated, which result from scattering assistant phase-matching processes.

Fully automated dual-frequency three-pulse-echo 2DIR spectrometer accessing spectral range from 800 to 4000 wavenumbers.

A novel dual-frequency two-dimensional infrared instrument is designed and built that permits three-pulse heterodyned echo measurements of any cross-peak within a spectral range from 800 to 4000 cm(-1) to be performed in a fully automated fashion. The superior sensitivity of the instrument is achieved by a combination of spectral interferometry, phase cycling, and closed-loop phase stabilization accurate to ~70 as. The anharmonicity of smaller than 10(-4) cm(-1) was recorded for strong carbonyl stretching modes using 800 laser shot accumulations. The novel design of the phase stabilization scheme permits tuning polarizations of the mid-infrared (m-IR) pulses, thus supporting measurements of the angles between vibrational transition dipoles. The automatic frequency tuning is achieved by implementing beam direction stabilization schemes for each m-IR beam, providing better than 50 μrad beam stability, and novel scheme for setting the phase-matching geometry for the m-IR beams at the sample. The errors in the cross-peak amplitudes associated with imperfect phase matching conditions and alignment are found to be at the level of 20%. The instrument can be used by non-specialists in ultrafast spectroscopy.

Non-collinear phase-matching geometries in optical parametric chirped-pulse amplification

This study presents a full three-dimensional nonlinear pulse propagation and amplification model that includes considerations for phase-matching, diffraction, and walk-off effects. By using this model, two types of type I non-collinear phase-matching geometries in BBO based optical parametric chirped-pulse amplification are investigated theoretically and experimentally. The simulation results agree well with the experimental findings.

Fully absorptive 3D IR spectroscopy using a dual mid-infrared pulse shaper.

This paper presents the implementation of 3D IR spectroscopy by adding a second pump beam to a two-beam 2D IR spectrometer. An independent mid-IR pulse shaper is used for each pump beam, which can be programmed to collect its corresponding dimension in either the frequency or time-domains. Due to the phase matching geometry employed here, absorptive 3D IR spectra are automatically obtained, since all four of the rephasing and non-rephasing signals necessary to generate absorptive spectra are collected simultaneously. Phase cycling is used to isolate the fifth-order from the third-order signals. The method is demonstrated on tungsten hexacarbonyl (W(CO)6) and dicarbonylacetylacetonato rhodium (I), for which the eigenstates are extracted up to the third excited state. Pulse shaping affords a high degree of control over 3D IR experiments by making possible mixed time- and frequency-domain experiments, fast data acquisition and straightforward implementation.