Types Of Phase Matching Research Articles

Investigation of Angle Measurement Based on Direct Third Harmonic Generation in Centrosymmetric Crystals

This paper proposed angle measurement methods based on direct third harmonic generation (THG) in centrosymmetric crystals. The principles of the intensity-dependent and the wavelength-dependent angle measurement methods were illustrated. In this study, three prospective centrosymmetric crystals and two different phase-matching types were investigated in a wavelength range from 900 nm to 2500 nm. For the intensity-dependent method, a dispersion-less wavelength range was found from 1700 nm to 2000 nm for α-BBO and calcite. Compared with rutile, α-BBO and calcite had relatively better measurement performance based on the angle measurement sensitivity calculation. The wavelength-dependent method was considered in a dispersive range of around 1560 nm. The results suggested that α-BBO and calcite were also suitable for wavelength-dependent measurement. In addition, the effects of focusing parameters were considered in the simulation, and the optimized focal length (f = 100 mm) and the focused position (in the center of the crystal) were determined.

Full characterization of spontaneous parametric down conversion in non-ideal quarter-wavelength semiconductor Bragg reflection waveguide

Entangled photons are important for testing foundations of quantum physics and are at the heart of quantum technology. Integrated photonics has overwhelming dominance in terms of density and performance, making it a promise route for scalable quantum information processing. AlGaAs-based materials having large second-order non-linearities, direct bandgap and strong electro-optical effect can offer distinct advantages in quantum light source. Here we report a non-ideal quarter-wavelength Bragg reflection waveguide for generating three types of spontaneous parametric down-conversion processes. A general solution to the dispersion equation is derived and employed for designing high efficiency devices by taking into account the influence of core layer aluminium concentration. We further design and fabricate a Bragg reflection waveguide sample based on the analysis, and experimentally characterize its phase matching types and spectral brightness. Our work paves the path for the development of portable quantum light sources.

Investigation on the optical characteristic of calcite crystal and α-BBO crystal in direct third-harmonic generation process

Calcite crystal and α-BBO crystal of which the microstructure possesses symmetric center with delocalized π bond were selected to produce phase-matched direct third-harmonic. In order to obtain a high third-order nonlinear conversion efficiency, the parameters including the walk-off angles, phase-matching angles, acceptance angles, acceptance wavelengths and group-velocity index in calcite crystal and α-BBO crystal were calculated within I (ooo→e), II (ooe→e) and III (oee→e) phase-matching types. The tinier walk-off angle and the larger acceptance angle in α-BBO crystal may lead to a better third-order nonlinear interaction in UV region. The smaller phase-matching angle in calcite crystal makes it possible to produce third-harmonic with shorter wavelength even in deep UV region. In the experiment, phase-matching angles and phase-mismatching angles of type-II which was the most efficient phase-matching type were measured in calcite crystal and α-BBO crystal. The results may provide a reference for further study on direct third-harmonic generation.

Angular engineering strategy of an additional periodic phase for widely tunable phase-matched deep-ultraviolet second harmonic generation

Manipulation of the light phase lies at the heart of the investigation of light-matter interactions, especially for efficient nonlinear optical processes. Here, we originally propose the angular engineering strategy of the additional periodic phase (APP) for realization of tunable phase matching and experimentally demonstrate the widely tunable phase-matched second harmonic generation (SHG) which is expected for dozens of years. With an APP quartz crystal, the phase difference between the fundamental and frequency-doubled light is continuously angularly compensated under this strategy, which results the unprecedented and efficient frequency doubling at wavelengths almost covering the deep-UV spectral range from 221 to 332 nm. What’s more, all the possible phase-matching types are originally realized simultaneously under the angular engineering phase-matching conditions. This work should not only provide a novel and practical nonlinear photonic device for tunable deep-UV radiation but also be helpful for further study of the light-matter interaction process.

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.

Generation of few-cycle radiation pulses in the IR spectral range (1.3 – 2.2 μm) using wide-aperture BBO crystals pumped by a terawatt Ti : sapphire laser * *Presented at the 4th International Conference on Ultrafast Optical Science (Russia, Moscow, FIAN, 28 September – 2 October 2020).

Different schemes of parametric amplification (PA), aimed at designing a source of femtosecond near-IR (1.3 – 2.2 μm) radiation, are compared by solving a system of truncated equations describing three-wave mixing. A terawatt Ti : sapphire laser with an energy of 60 mJ and a pulse duration of 50 fs is used as a pump source for PA schemes. The dependences of the output energies, pulse durations, and spectral widths of signal and idler waves on the BBO crystal length for two types of phase matching and on the group-delay dispersions for the pump and signal waves is investigated. It is shown that in the case of direct PA, using a type-II phase-matching BBO crystal of optimal length, one can obtain signal (1.333 μm) and idler (2 μm) waves with pulse durations of 34 and 32 fs, respectively, with a total energy conversion efficiency up to 40 %. The application of double chirping scheme increases the total conversion efficiency to 60 %; however, the spectral width of generated pulses decreases. The spectral width can only be increased by reducing the conversion efficiency. In this case, a more simple and compact solution is the scheme of direct PA with a transform-limited pump pulse.

Temperature tuning of BaGa4Se7 optical parametric oscillator

The temperature tuning of BaGa4Se7 (BGSe) was demonstrated for the first time, to the best of our knowledge. When the temperature of BGSe (56.3°,0°) was raised from 30°C to 140°C, the idler light under type I raised from 3637 nm to 3989 nm, the tunable range reached 352 nm, and Δλ2/ΔT reached 3.20 nm/°C. We calculated the phase matching curve of BGSe when ∅ and T took different values. The relationship between θ and Δλ2/ΔT was obtained by fixing ∅ at 0°. The maximum Δλ2/ΔT and its corresponding (θ, ∅) phase matching type were reported under different fixed λ2 (3 µm, 3.2 µm,…, 5 µm).

Growth of large aperture LBO crystal applied in high power OPCPA schemes

LBO crystal up to 192 × 130 × 89 mm3 in size and 2327 g in weight has been grown by TSSG method and cut into an optical element with a size of 100 mm × 100 mm × 17 mm for critically phase-matched type I (θ = 90°, Ø = 13.85°). Near phase-matching direction growth was introduced to promote yield of the final large aperture LBO elements greatly from the limited mass of crystal. Take into consideration of crystallographic symmetry, the linear thermal expansion coefficients and crystal growth habit, LBO grown along [1 0 0] direction was proved to be the best choice to produce large element which meet the demands of high power OPCPA schemes. The grown LBO crystal possesses high optical quality, and shows no evidence that crystal growth modifications have detrimental influence on the crystal property. The laser-induced damage threshold (LIDT) at λ = 1064 nm and τ = 5 ns is 42 J/cm2 for 1-on-1 type tests. Absorption at 1064 nm has been found to be 10–20 ppm/cm at 1064 nm). Especially, the optical homogeneity reached 1.9 × 10−7 cm−1 in full aperture for the optical elements mentioned above, to the best of our knowledge, the highest optical homogeneity in borate crystals. This extremely high optical homogeneity, large aperture optical element of LBO is more favorable in the high power laser schemes.

Simultaneous generation of two THz waves with bulk LiNbO3 and four THz waves with PPLN by coupled optical parametric generation

We present a theoretical research concerning simultaneous generation of two terahertz (THz) waves with bulk LiNbO3 and four THz waves with periodically poled LiNbO3 (PPLN) by coupled optical parametric generation (COPG). First, we investigate collinear phase matching of COPG generating two orthogonally polarized THz waves with two types of phase matching of o = e + e and o = e + o with bulk LiNbO3. The two orthogonally polarized THz waves are generated from stimulated polariton scattering (SPS) with A1 and E symmetric transverse optical (TO) modes in bulk LiNbO3, respectively. Then, we find that perturbations of phase mismatch for o = e + e and o = e + o can be compensated by a same grating vector of PPLN. As a result, four THz waves are simultaneously generated with a PPLN crystal and a pump laser. We calculate third-order nonlinear optical coefficients of o = e + o generating THz waves from E symmetric TO modes. The intensities of four THz waves are calculated by solving coupled wave equations. The calculation results demonstrate that the COPG generating four THz waves have high photon conversion efficiencies.

Study on long-wave infrared ZnGeP2 subsequent optical parametric amplifiers with different types of phase matching of ZnGeP2 crystals

Pumped by a 100 W Q-switched Ho:YAG laser at 2090.7 nm with pulse repetition frequency of 10 kHz, four types of high-power long-wave infrared ZnGeP2 (ZGP) subsequent optical parametric amplifier (OPA) based on optical parametric oscillator (OPO) with different types of phase matching (PM) of ZGP crystals were demonstrated. For the results of 8.2 µm output characteristics at the full incident pump power, Type-II PM ZGP OPO with Type-II PM ZGP OPA had the best M2 of 1.8 and lowest average output power of 9.2 W with the narrowest linewidth of 77 nm, while Type-I PM ZGP OPO with Type-I PM ZGP OPA had the worst M2 of 2.2 and the widest linewidth of 122 nm, and Type-II PM ZGP OPO with Type-I PM ZGP OPA had the highest average output power of 12.6 W, corresponding to overall optical conversion efficiency of 12.6% from Ho to long-wave infrared laser system.

Ultra-broadband SPDC for spectrally far separated photon pairs.

Photon pairs from spontaneous parametric down-conversion (SPDC) are important for a wide range of quantum optics experiments with spectral properties such as their bandwidths often being a crucial concern. Here we show the generic existence of particular phase-matching conditions in quasi-phase-matched KTP, MgO:LN, and SLT crystals that lead to ultra-broadband, widely nondegenerate photon pairs. It is based on the existence of group-velocity-matched, far apart wavelength pairs and, for 2mm long crystals, results in SPDC bandwidths between 15 and 25THz for photon pairs with the idler photon in the technologically relevant mid-IR range of 3-5μm and the signal photon in the near-IR below 1100nm. We experimentally demonstrate this type of broadband phase matching in ppKTP crystals for photon pairs centered at 800 and 3800nm and measure a bandwidth of 15THz. This novel method of generating broadband photon pairs will be highly beneficial for SPDC-based imaging, spectroscopy, refractometry, and optical coherence tomography with undetected mid-IR photons.

Theoretical investigation of second harmonic efficiency effect on third harmonic conversion efficiency in BBO crystals

A general relation of nanosecond third harmonic conversion efficiency has been concluded with taking the effect of second harmonic efficiency for the first time to determine THG efficiency at any value of power density, laser wavelength, crystal length, second harmonic conversion efficiency and beam divergence when transmission value are relative high >90%, which make it a reference for practical study comparison. We apply this study on BBO THG crystal and study the THG conversion efficiency as function of both (SHG and THG) crystal lengths (0-0.7 cm) and laser wavelength (690–1350 nm) in 3-D plot for four phase matching types (SHG I/THG I, SHG I/THG II, SHG II/THG I, SHG II/THG II). Finally, we compare the efficiency of SHG and THG for generated wavelength 205 nm for same power density and crystal length ranges, then we generalized the comparison to generated wavelength range (205–450 nm) for crystal length 0.1 cm. The results shown a higher conversion efficiency for THG (I/I) over SHG (I) in generated wavelength range (205–269 nm) when crystal length is 0.1 cm.

A high energy, wavelength and repetition rate tunable eye-safe picosecond optical parametric oscillator

A wavelength and pulse repetition rate (PRR) tunable eye-safe picosecond (ps) optical parametric oscillator (OPO) with high energy is developed using a novel method that operates the OPO in a ps regenerative amplifier (RA). With this method, the PRR can be conveniently tuned and a compact kHz ps OPO can be achieved with a pulse energy of 1–3 orders of magnitude higher than previous works. Based on an angle phase matching type II (θ = 41.4°, φ = 0°) KTA crystal, signal wavelength tunability from 1501 nm to 1565 nm is realized at the PRRs of 5 kHz and 10 kHz, respectively. The highest pulse energy of 21.6 µJ with a pulse width of about 6 ps is obtained at the PRR of 5 kHz and a wavelength of 1532 nm.

Non-collinear phase-matching sum-frequency generation based on boundary total reflection in bulk KDP

Collinear phase-matching of sum-frequency generation (SFG) has been studied thoroughly previously, while non-collinear schemes are sometimes more flexible in application. However, this phase-matching type is more difficult to meet and control. We employ a convenient method to obtain harmonic generation in bulk potassium dihydrogen phosphate (KDP), using an incident wave vector and a reflected wave vector to create a triangle phase-matching relationship. With a simple, flexible set-up, we can observe 351 nm SFG, and the conversion efficiency is up to ∼3.6% per reflection. Furthermore, we believe this approach has potential application value and improvement space.

Simultaneous Generation of Two Orthogonally Polarized Terahertz Waves by Stimulated Polariton Scattering with a Periodically Poled LiNbO3 Crystal

We present a theoretical investigation of the simultaneous generation of two orthogonally polarized terahertz (THz) waves by stimulated polariton scattering (SPS) with a periodically poled LiNbO3 (PPLN) crystal. The two orthogonally polarized THz waves are generated from SPS with A1 and E symmetric transverse optical (TO) modes in a LiNbO3 crystal, respectively. The parallel polarized THz wave is generated from A1 symmetric TO modes with type-0 phase-matching of e = e + e, and the perpendicular polarized THz wave is generated from E symmetric TO modes with type-I phase-matching of e = o + o. The two types of phase-matching of e = e + e and e = o + o can be almost satisfied simultaneously by accurately selecting the poling period of the PPLN crystal. We calculate the photon flux density of the two orthogonally polarized THz waves by solving the coupled wave equations. The calculation results indicate that the two orthogonally polarized THz waves can be efficiently generated, and the relative intensities between the two orthogonally polarized THz waves can be modulated.

Theoretical investigation of phase-mismatched second-harmonic conversion efficiency in BBO crystal

We report a modified general relation of nanosecond second harmonic conversion efficiency relation to determine efficiency at any value of power density, laser wavelength, crystal length and beam divergence when transmission value are relative high >90%, which make it a reference for practical study comparison. We apply this study on BBO crystal and study the efficiency as function of both crystal length (0–0.7 cm) and laser wavelength (460–1400 nm), (527–1400 nm) in 3-D plot for phase matching types I and II respectively. Finally, we study the effect of crystal length and power density at generated deep-ultraviolet cut-off type I wavelength 205 nm.

Temperature-insensitive frequency conversion by phase mismatch self-compensation in the same type of crystals.

Aiming at high-power laser frequency conversion, we present a new scheme that can self-compensate for the thermally induced phase mismatch. The basic design of the scheme is that three crystals with the same type are cascaded, of which the crystals at both ends are used for frequency conversion and the middle crystal is used for compensating phase mismatch. By configuring the polarization states of the interacting waves in the middle crystal, the sign of the first temperature derivative of the phase mismatch is opposite to that of the frequency conversion crystals. The thermally induced phase mismatch in the first crystal can thus be self-compensated in the middle crystal. To verify the utility of the proposed scheme, we experimentally demonstrated temperature-insensitive second and third harmonic generation using KH2PO4 crystals. The results show that the temperature acceptance bandwidth is about two times larger than that of using a single crystal. Since the crystals used are of the same type, this scheme has excellent universal applicability and is almost completely free from the limitations of the laser wavelength, crystal and phase-matching type. Therefore, the scheme can be widely applied to various frequency conversion processes and is scarcely any limitations.

Second harmonic generation of off axial vortex beam in the case of walk-off effect

Process of off axial vortex beam propagating in negative uniaxial crystal is investigated in this work. Firstly, we get the formulae of the normalized electric field and calculate the location of vortices for second harmonic beam in two type of phase matching. Then, numerical analysis verifies that the intensity distribution and location of vortices of the first order original vortex beam depend on the walk-off angle and off axial magnitude. It is shown that, in type I phase matching, the distribution of vortices is symmetrical about the horizontal axis, the separation distance increases as the off axial magnitude increases or the off axial magnitude deceases. However, in type II phase matching, the vortices are symmetrical along with some vertical axis, and increase of the walk-off angle or off axial magnitude leads to larger separation distance. Finally, the case of high order original off axial vortex beam is also investigated.

Efficient phase-matching for difference frequency generation with pump of Bessel laser beams.

A type of phase matching for difference frequency generation with Bessel-type pump beams is proposed. In this geometry, the phase matching is achieved in a cone around the laser path by properly controlling the beam profile. An experimental case that 1.5THz generation with ~2μm lasers pumped bulk GaAs crystal is considered. Calculations of the energy conversion characteristics are performed based on a semi-analytical model. The results indicate that this configuration could relax the phase matching condition in a wide range of nonlinear crystals and pump wavelengths.

A novel numerical technique for simultaneous calculations of type II phase matching angle and temperature for second harmonic generation in negative uniaxial crystals

In the present work, the phase matching type II conditions using birefringence for second harmonic generation (SHG) in negative uniaxial crystals were studied. A novel numerical method allowing the simultaneous and reliable calculations of the type II phase matching angle and temperature versus fundamentals wavelengths for SHG in Lithium Niobate (LiNbO3) was proposed. The angles and temperatures were determined for values less or equal to 5×10−6 of uncertainty. Indeed, SHG efficiency curves at fundamental frequency f=1.6 THz obtained for various error values highlighted the validity and accuracy of the calculations. The proposed method was also applied in the case of the type I phase matching SHG using both the same crystal and precision. A good agreement between the analytical and numerical results was obtained.