Noncritical Phase Matching Research Articles

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.

Double-pass pumping KTA OPO based on unstable resonator with Gaussian reflectivity mirror

A novel double-pass pumping optical parametric oscillator (OPO) with unstable resonator based on Gaussian reflectivity mirror (GRM) was proposed and demonstrated. The output characteristics of double-pass pumping OPO based on non-critical phase matching (NCPM) KTiOAsO4 (KTA) crystal were researched at a pulse repetition frequency of 100 Hz. Compared with the single-pass pumping OPO, the output energy and the conversion efficiency of double-pass pumping OPO were improved by 36 %. The beam qualities of signal and idler were measured and compared with different pump structures, and the results show that beam quality of signal for double-pass pumping OPO barely deteriorated. In addition, the pulse widths of signal and idler under two pumping structures and their variation trends with different pump energies were researched and compared.

First Principle Study of Electronic, Optical and Thermoelectric Properties of CuInS2 and CuInSe2

We report the bandgap, thermoelectric and optical properties of CuInS2 and CuInSe2 ternary chalcopyrite compounds based on DFT calculations. Our calculations shows that both CuInS2 and CuInse2 have a direct bandgap which were at the Γ-points. The computed bandgap were 1.35 and 0.85 eV for CuInS2 and CuInSe2. The optical properties analysis shows that the fundamental edge of absorption arise at 0.82 eV and 0.35 eV along the perpendicular and parallel polarization for CuIns2, while it arise at 0.13 eV and 0.16 eV along the perpendicular and parallel polarization for CuInSe2. The static dielectric constant, static refractive index and birefringence were then calculated. The calculated birefringence was negative, which meets the non-critical phase matching (NCPM) requirement, which is beneficial for high-performing laser systems. The optical absorption threshold lies at 1.4, and 0.83 eV for CuInS2 and CuInSe2. These compounds shows low reflectivity and high absorption in the visible region. Both compounds have high electrical conductivity and Seebeck coefficient, making them promising candidates for thermoelectric devices.

High efficiency non-critical phase-matching 9.3–10.6 μm optical parametric oscillator in BaGa4Se7 crystal

In this letter, a non-critical phase-matching (NCPM) BaGa4Se7 (BGSe) optical parametric oscillator (OPO) was demonstrated with a home-made acousto-optic (AO) Q-switched Ho:YLF laser as the pump source. The idler wavelength tunability was recorded to be 9393.3 to 10627.4 nm with BGSe crystal temperature varying from 45 to 5 Celsius (˚C), corresponding to an average wavelength adjustment of 30.85 nm/˚C. Up to 200 mW of idler average output power at 10219 nm was obtained with pulse repetition frequency (PRF) at 200 Hz, the slope efficiency and pump-to-idler efficiency are 8.04 % and 5 %, respectively. In addition, in the angle tuning experiment, a refined Sellmeier Equation (S-E) was derived based on the discrepancy between the experimental data and the theoretical calculations based on the existing S-Es. However, it was found that the deviations between experimental measurement data and theoretical calculations in NCPM experiment were still too large to be ignored after using the refined S-E. Probably, the phenomenon was caused by the thermo-optic dispersion formula dn/dT provided by references were not precise enough for describing NCPM BGSe crystal in waveband ∼ 10 μm.

Topological evolution of acousto-optic transfer functions in biaxial crystals

Modern applications of acousto-optic tunable filters (AOTFs) range from hyperspectral imaging in space research and biomedical optics to optical manipulation and ultrafast laser pulse shaping. The design of all AOTFs is based on optical anisotropy of crystals; until now, however, only uniaxial crystals have been used. Lower symmetry and outstanding acousto-optic (AO) properties of some new biaxial crystals make them promising candidates for qualitative improvements in this field. Anisotropic AO interaction in crystals allows angular noncritical phase-matching (NPM) configurations that are commonly used in different AOTF types. In this work, we perform a comprehensive geometrical and topological analysis of 2D transfer functions of AO interaction under NPM condition in biaxial crystals. The topological classification of the 2D transfer functions under an angular NPM condition is proposed. In principle, in the planes of a biaxial, the same types of transfer function exist as in uniaxial crystals, including cross-like topology of collinear diffraction, circular topology, and ultrawide angle topology. In addition, new topological types of the AO 2D transfer function are reported, which exist only in biaxial crystals.

220 nm deep-UV coherent source based on fifth-harmonic generation in ADP and DKDP crystals

Based on the 1.1 μm laser radiation obtained by parametrically amplifying Yb:YAG laser using frequency doubling of Nd:YAG laser, a 220 nm deep-UV coherent source was systematically presented via the efficient fifth-harmonic generation (FiHG) in NH4H2PO4 (ADP) and KD2PO4 (DKDP) crystals. In ADP crystals, noncritical phase-matching (NCPM) fourth-harmonic generation (FHG) and FiHG were realized at 109.4 and 31.6 °C, respectively. For DKDP crystals, we demonstrated the critical phase-matching FHG at 57.5 °C and verified that NCPM FiHG can be achieved at 38.7 °C, which was the first demonstration of the FiHG using the DKDP crystal to our knowledge. The energy-dependent conversion efficiencies, angular acceptances, and temperature acceptances of these nonlinear processes were systematically measured. The highest total conversion efficiencies from 1.1 μm to the fifth harmonic in ADP and DKDP crystals were 17.5% and 23.6%, respectively. Owing to the large-aperture availability of KDP-family crystals, this work paves the way for the generation and application of high-energy and high-peak-power deep-UV laser radiation.

Self-cascaded noncritically-phase-matched KTP optical parametric oscillator for generating orthogonally polarized multi-wavelength emissions at 3 μm

Mid-infrared self-cascaded noncritically-phase-matched (NCPM) KTP optical parametric oscillator (OPO) was developed, generating multiple wavelengths at 2.95, 3.29 and 3.37 μm. The polarization state of 2.95 μm is orthogonal to that of the other two wavelengths. Under 1064 nm intracavity pumping, the first NCPM KTP-OPO can generate signal and idler waves at 1.57 and 3.29 μm, respectively. Then the 1.57 μm is further used as pump light for the second NCPM OPO in the same KTP, generating signal and idler waves at 2.95 and 3.37 μm. Broadband spectral feedback condition is established between the OPO cavity mirrors, enabling the two NCPM OPOs to operate simultaneously in the same KTP and OPO resonator. With regard to 2.95 μm, the achieved maximum average output power and minimum pulse width are respectively 1.18 W and 5 ns, corresponding to a pulse peak power of 56.9 kW with 4.2 kHz repetition rate. As for the dual-wavelength at 3.29 and 3.37 μm, the maximum total average output power is 0.22 W. Our work provides an effective scheme to obtain multiple wavelength laser output in 3 μm region with orthogonal polarization state.

Noncritical phase-matching fourth- and fifth-harmonic generation of 1077 nm laser using KDP-family crystals.

We systematically demonstrated the angular and temperature acceptances of noncritical phase-matching (NCPM) fourth- and fifth-harmonic generation (FHG and FiHG) of a 1077 nm laser in NH4H2PO4 (ADP), KH2PO4 (KDP), and KD2PO4 (DKDP) crystals. In this work, a new, to the best of our knowledge, laser frequency with a wavelength of 1077 nm was generated by optical parametric amplification, in which the pump light (526.3 nm) was generated by the frequency doubling of a Nd:YLF laser (1052.7 nm), and the signal light was a Yb:YAG laser (1029.5 nm). Subsequently, the 1077 nm laser was used as the fundamental wave for FHG and FiHG to obtain a deep-ultraviolet laser source. For ADP and DKDP crystals, NCPM FHG of a 1077 nm laser was realized at 74.0∘C and 132.5∘C, respectively, and large angular acceptances of 59.8 and 61.6 mrad were measured. For the FiHG, NCPM was realized in a KDP crystal at 48.5∘C with an angular acceptance of 56.4 mrad. The results pave the way for high-energy and high-power deep-ultraviolet laser generation using KDP-family crystals under noncryogenic conditions.

Compact 589 nm yellow source generated by frequency‐doubling of passively Q‐switched Nd:YVO4 Raman laser

AbstractCompact 589 nm yellow source was reported and generated from intracavity frequency‐doubling of c‐cut YVO4/Nd:YVO4/YVO4 Raman laser. A Cr4+:YAG/YAG composite was adopted for compact passively Q‐switching operation. Double‐end composited Nd:YVO4 crystal was designed to reduce the thermal effect and increase Raman crystal length. Both noncritical phase‐matching (NCPM) LBO crystal and critical phase‐matching (CPM) BBO crystal were used as frequency doubling crystal for comparison. 780 mW output power of 589 nm yellow emission was achieved with an incident pump power of 16 W. The pulse repetition frequency and pulse width were 41 kHz and 3.6 ns at the maximum output power, respectively. The results show passively Q‐switched operation provides a compact method to obtain 589 nm yellow emission.

Noncritical phasematching behavior in thin-film lithium niobate frequency converters.

We present a study of noncritical phasematching behavior in thin-film, periodically poled lithium niobate (PPLN) waveguides. Noncritical phasematching refers to designing waveguides so that the phasematching is insensitive to variations in waveguide thickness, width, or other parameters. For waveguide thickness (the dimension with greatest nonuniformity due to fabrication), we found that phasematching sensitivity can be minimized but not eliminated. We estimate limits on the acceptable thickness variation and discuss scaling with device length for second-harmonic generation and sum-frequency generation in thin-film PPLN frequency converters.

Optical beam diffraction tensor in birefringent crystals

We demonstrate that anisotropy of Fresnel diffraction in a birefringent medium can be quantitatively characterized by a planar tensor. Eigenvectors of the tensor correspond to directions of minimum and maximum beam divergence. Zero eigenvalues exist for the slow eigenmode near the optic axis of biaxial crystals and correspond to autocollimated beam propagation along the cone of external conical refraction. Applications of the beam diffraction tensor are demonstrated for analysis of noncritical phase matching in acousto-optics and nonlinear three-wave mixing.

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.

321 W high-efficiency continuous-wave green laser produced by single-pass frequency doubling of narrow-linewidth fiber laser.

In this study, a high-power continuous-wave green laser for copper processing is investigated. The laser is produced by single-pass second-harmonic generation (SHG) of a narrow-linewidth fiber laser. Based on Sellmeier equations, the factors (e.g., fundamental wave linewidth, temperature, and angle) that decide LBO noncritical phase matching are theoretically analyzed for optimizing the SHG setup. A narrow-linewidth polarization-maintained fiber laser is used as the fundamental laser with a linewidth of 20 GHz and polarization extinction ratio of greater than 15 dB. Type I noncritical phase-matching LBO is used as the nonlinear crystal in the SHG. A green laser (up to 321 W) is obtained from a 784 W fundamental laser with a conversion efficiency of 40.9%. The green laser is near-diffraction-limited and has a $ M^{2} $ factor of 1.07.

Efficient third-harmonic generation of broadband picosecond radiation by employing spectrally noncritical phase-matching KDP crystal and cascaded LBO crystals

To improve the nonlinear frequency conversion efficiency of a broadband picosecond fiber laser, the spectrally noncritical phase matching for frequency doubling, dual-crystal cascaded design for frequency tripling is employed. By this method, we obtain 2.39 W of output power at the third-harmonic wavelength, when the spectral full width at half maximum of the fundamental light is 5.5 nm and the input fundamental light power is 8.6 W. The frequency conversion efficiency of IR-UV is 27.8%. To the best of our knowledge, this is the first time of the broadband third harmonic picosecond ultraviolet laser generation by the combination of the spectrally noncritical phase matching for frequency doubling and dual-crystal cascaded design for frequency tripling.

4 mJ Rectangular- Envelope GHz-Adjustable Burst-Mode Fiber-Bulk Hybrid Laser and Second-Harmonic Generation

We demonstrate a high peak power and high burst energy linear-polarization, narrowband, GHz-adjustable burst-mode fiber-bulk hybrid laser with central wavelength of 1064 nm and its second-harmonic generation. The active modulated burst-mode seed provides the tunability of temporal parameters and the pre-compensation of burst envelope distortion. Three-stage polarization maintained fiber amplifier cascading bulk amplifier promote the burst energy to 4 mJ at a burst duration of 100 ns and intra-burst duty of 50%. To the best of our knowledge, this is the highest reported output energy of burst-mode fiber-bulk hybrid laser with ∼ hundred nanoseconds burst duration. Also, the pre-compensation for rectangular burst envelope is investigated by iteration method. Type I, non-critical phase matching lithium borate (LBO) is employed for second-harmonic generation and 1.8 mJ burst energy is achieved, corresponding to a conversion efficiency of 45%. The 3 dB spectral width of green light at maximal burst energy is 90 pm. The immediate application of this laser system is the generation of high peak power frequency-adaptive microwave.

High-efficiency, fifth-harmonic generation of a joule-level neodymium laser in a large-aperture ammonium dihydrogen phosphate crystal.

High-energy deep ultraviolet (UV) sources are required for high-density plasma diagnostics. The fifth-harmonic generation of large-aperture neodymium lasers in ammonium dihydrogen phosphate (ADP) can significantly increase UV energies due to the availability of large ADP crystals. Noncritical phase matching in ADP for (ω + 4ω) was achieved by cooling a 65 × 65-mm crystal in a two-chamber cryostat to 200 K. The crystal chamber used helium as the thermally conductive medium between the crystal and the crystal chamber, which was surrounded by a high-vacuum chamber with a liquid nitrogen reservoir. A temperature variation of 0.2 K across the crystal aperture was obtained. The total conversion efficiency from the fundamental to the fifth harmonic at 211 nm was 26%.

Frequency doubling of acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded Raman laser for narrow pulse-width 657 nm laser

Frequency doubling of second-Stokes in an acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded self-Raman cavity is demonstrated to achieve a narrow pulse-width red laser. A three-stage bonded YVO<sub>4</sub>/Nd:YVO<sub>4</sub>/YVO<sub>4</sub> crystal is designed by comprehensively considering the improvement of thermal effect, the performance of fundamental frequency laser and Raman conversion, to improve the Raman efficiency and output power. An LBO crystal cut for critical phase matching at room temperature is selected and used as a nonlinear optical crystal for realizing the frequency doubling of second- Stokes wave. Its phase matching angle (<i>θ</i> = 86.0°, <i>φ</i> = 0°) is very close to the non-critical phase matching angle and has a small walk-off angle, which is beneficial to the realizing of the high conversion efficiency of frequency doubling. In the experiment, the beam waist position of the pump light and the repetition frequency of the acousto-optic Q-switcher are optimized. Under an incident pump power of 14.2 W and a repetition frequency of 60 kHz, the highest average output power of 1.63 W and conversion efficiency of 11.5% are obtained for the 657 nm red laser emission. The pulse width of 657 nm red light is 11.5 ns at the maximum output power, which is much narrower than that generated by frequency doubling of ordinary neodymium-doped laser at a waveband of 1.3 μm. The result shows that the frequency doubling of the acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded self-Ramanlaser can take advantage of the pulse-width compression characteristics of Raman process to achieve a narrower pulse-width red light laser output.

Widely Tunable Angular Non-Critical Phase-Matching Wavelengths from 0.72 to 1.42 μm Based on RE1xRE21−xCOB Mixed Crystals

The angular non-critical phase-matching (A-NCPM) second-harmonic-generation (SHG) properties of RE1xRE21−xCOB (RE1, RE2 = Y, Gd, La, Tm, Sm, and Nd) type mixed crystals including NCPM wavelength and conversion efficiency were detailedly investigated. Theoretical calculations manifest that the A-NCPM SHG scope of these crystals is 0.72~1.42 µm, and in experiments, the A-NCPM SHG waveband of 0.72~1.25 µm has been realized, by changing the ratio of the rare-earth elements RE1 and RE2 in RE1xRE21−xCOB crystals. Comparing to the temperature-dependent A-NCPM SHG of 0.95~1.34 µm in LiB3O5 (LBO) crystal, the composition-dependent A-NCPM SHG of 0.72~0.95 µm in RE1xRE21−xCOB type crystals is unique and has special significance for the frequency conversion of Ti:Sapphire lasers. Relationships between the birefringence and radius of rare-earth ion RE3+ in RE1xRE21−xCOB mixed crystals were discussed. Aiming for the A-NCPM SHG of 0.72~1.42 µm, we supply a clear, completed, and optimized solution on how to select the compositions of RE1xRE21−xCOB mixed crystals. Under focusing light beam conditions, high efficient A-NCPM SHG for both OPO and Ti:sapphire lasers were realized experimentally by using long Y- and Z-cut RE1xRE21−xCOB crystal samples.

High-power and high-energy Nd:YAG-Nd:YVO4 hybrid gain Raman yellow laser.

We present a simple and reliable method to successfully reconcile the average output power and pulse energy of the solid-state Raman yellow lasers. By virtue of the hybrid laser gain of Nd:YAG and Nd:YVO4 in an intracavity frequency-doubled Raman, much higher pumping is allowed and nearly linear polarized fundamental and Stokes waves can be delivered for efficient non-critical phase matching. 7.6 W of yellow output at 588 nm is obtained under incident pump power of 42.0 W at the pulse repetition frequency (PRF) of 110 kHz and the pulse energy reaches 0.41 mJ under the same incident pump power at the PRF of 10 kHz.

A Fiber-Based High-Power Single Frequency Pulsed Laser at 780 nm/776 nm for Rb Dating

We report on the generation of 7.6 ns, 162 μJ and 21.3 kW (peak power) single-frequency optical pulses at 780 nm with near-diffraction limited beam quality (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <; 1.1) from a frequency-doubled all-fiber MOPA system for a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">87</sup> Rb based dating application. Frequency doubling is performed in 4-cm long non-critically-phase-matched (NCPM) LBO crystal with a measured conversion efficiency of ~50%. The same technology has also been used to build another similar pulsed laser at 776nm. To the best of our knowledge, this is the highest pulse energy and peak power in a single-frequency laser near 780nm with near-Gaussian beam quality obtained from a frequency-doubled all-fiber MOPA system. The use of the all-fiber MOPA configuration allowed us to develop compact and rugged laser systems at both 780nm and 776nm for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">87</sup> Rb dating applications.