Temperature Acceptance Bandwidth Research Articles

Generation of 116 mW output power at 461 nm in a periodically poled lithium niobate waveguide

We demonstrate a second harmonic generation (SHG) of 116 mW at 461 nm in a periodically poled lithium niobate waveguide when the power of the 922 nm fundamental light is coupled into the waveguide was 350 mW. The waveguide is 12.5 μm wide, 12.0 μm thick, 22 mm long, and has a 1 mm long slab window at the output facet of the waveguide. The temperature acceptance bandwidth of the phase-matching curve of the SHG is approximately 0.5 °C. The SHG system demonstrates good beam quality and is reliable for cold atom experiments, including research on optical lattice clocks.

Phase Compensation Method in OPA System Based on the Linear Electro-Optic Effect

Factors such as mechanical deformation and temperature changes lead to phase mismatch in optical parametric amplification systems, impacting energy stability. A phase compensation method via the linear electro-optic effect can overcome this limitation. Phase mismatch compensation characteristics were simulated via the linear electro-optic effect in 70%-deuterated DKDP and 95%-deuterated DKDP. This method was applied to OPA systems to verify its feasibility. The results show that the temperature acceptance bandwidth of 70%-deuterated DKDP and 95%-deuterated DKDP can be ~1.75 and ~2 times larger, respectively, than that of the OPA without compensation. Moreover, the angle acceptance bandwidth of 70%-deuterated DKDP and 95%-deuterated DKDP can be ~2 times larger than that of the OPA without compensation. The abovementioned method can facilitate the compensation of phase mismatch within a range and can be widely used in OPA and optical parametric chirped pulse amplification systems to improve laser stability.

Broadband second-harmonic and sum-frequency generation with a long-wave infrared laser in AgGaGe5Se12.

Using an 8 µm long-wave infrared laser as the fundamental wave, we achieved second-harmonic generation (SHG) and sum-frequency generation simultaneously in AgGaGe5Se12 and obtained a 4 µm laser output. Among them, SHG was achieved in the 173 nm spectral range of the fundamental wave, which was consistent with theoretical calculations. The average power of the obtained 4 µm laser was 41 mW, corresponding to an optical-to-optical conversion efficiency of 3.2%. The measured temperature acceptance bandwidth (LδT) (FWHM) was 50 K·cm; the angular acceptance bandwidth (Lδθ) (FWHM) was 13.3 mrad·cm; and the average absorption coefficient in the wavelength range of 0.86-11.30 µm was 0.07cm-1. In addition, the spectral acceptance bandwidth (Lδλ) of fundamental wave in AgGaGe5Se12 SHG and the spectral gain bandwidth of frequency downconversion in AgGaGe5Se12 were calculated. In view of the small absorption coefficient, the large temperature acceptance bandwidth, and the large spectral gain bandwidth, we conclude that AgGaGe5Se12 is a suitable nonlinear crystal for high-power short/mid/long-wave infrared lasers and frequency conversions of nanosecond-femtosecond infrared lasers. These results are conducive to the further development of AgGaGe5Se12 lasers.

Adiabatic nonlinear optical frequency conversion based on the electro-optic effect

We propose a novel, to the best of our knowledge, adiabatic nonlinear optical frequency conversion method based on the electro-optic effect, which can be applied in a plethora of bulky nonlinear crystals. Within our method, an electric field gradient is applied on the crystal, which causes the phase mismatch to also gradually vary in space, thus achieving adiabatic frequency conversion. We demonstrate the validity and feasibility of this new approach by providing a theoretical framework and experimental evidence. In the experiment, the second harmonic generation of 532 nm is conducted in K D 2 P O 4 . Conversion efficiency approaching 47.2% is achieved, with a corresponding temperature acceptance bandwidth of 4.56°C, which is about 4.3 times the temperature without the external electric field. We argue that the approach based on the electro-optic effect is promising for extending the range of applications of adiabatic frequency conversion and, consequently, for achieving efficient and robust frequency conversion.

Multimilliwatt, tunable, continuous-wave, mid-infrared generation across 4.6-4.7 μm based on orientation-patterned gallium phosphide.

We report the generation of tunable continuous-wave (cw) mid-infrared (mid-IR) radiation across 4608-4694nm using the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). By exploiting difference-frequency mixing between a cw Tm-fiber laser and a home-built cw optical parametric oscillator in a 40-mm-long crystal, we have generated up to 43mW of cw output power, with >30 mW across >95% of the mid-IR tuning range. The output at 4608nm exhibits high beam quality with a passive power stability of 2.5%rms over 1.5min. The temperature acceptance bandwidth of the OP-GaP crystal has been measured and compared with theory. The performance of the mid-IR source at high pump powers and polarization-dependent transmission in OP-GaP has been investigated.

Performance characterization of mid-infrared difference-frequency-generation in orientation-patterned gallium phosphide

We present a detailed characterization of the optical properties of the recently developed nonlinear material, orientation-patterned gallium phosphide (OP-GaP), by performing difference-frequency-generation experiments in the 2548-2782 nm wavelength range in the mid-infrared (mid-IR). Temperature and spectral acceptance bandwidth measurements have been performed to study the phase-matching characteristics of OP-GaP, and the dependence of nonlinear gain on the polarization of input incident fields has been investigated. The transmission of the OP-GaP crystal at the pump and signal wavelengths has been studied and found to be dependent on polarization as well as temperature. Further, we have observed a polarization-dependent spatial shift in the transmitted pump beam through the OP-GaP sample. We have also measured the damage threshold of the OP-GaP crystal to be 0.84 J/cm2 at 1064 nm.

Temperature-insensitive sum frequency generation of 355-nm ultraviolet laser radiation in LiB3O5 by compensating thermally induced phase mismatch.

A temperature-insensitive sum frequency generation method based on thermally induced phase mismatch compensation is proposed to enhance the thermal stability and scale up the output power of ultraviolet (UV) lasers. In the method, three LiB3O5 crystals are cascaded for sum frequency generation of a 355-nm UV laser, and the two crystals at the ends are employed for frequency conversion; the middle one, which is not required to be phase matched and has an opposite sign of first temperature derivative of phase mismatch, compensates the thermally induced phase mismatch generated in the first crystal. The temperature acceptance bandwidth of frequency conversion in the three cascaded crystals is about double that in a single long crystal with the same interaction length.

级联晶体倍频器件温度适应性扩展研究

级联晶体倍频器件温度适应性扩展研究

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.

Temperature-insensitive frequency conversion by thermally-induced phase mismatch compensation using a non-phase-matched crystal

A simple and versatile thermally-induced phase mismatch compensation method by three cascaded nonlinear crystals is proposed and experimentally demonstrated for temperature-insensitive frequency conversion. The middle crystal, which is not required to be phase matched, compensates the thermally-induced phase mismatch generated in the first crystal. Additionally, the dispersion of air, which causes a phase shift between fundamental and harmonic waves, is utilized to reduce the demand of length accuracy of the middle crystal. The temperature acceptance bandwidth of frequency conversion in the three cascaded crystals is about double that in a single long traditional crystal with the same interaction length.

Nanosecond difference-frequency generation in orientation-patterned gallium phosphide.

We report a tunable, single-pass, pulsed nanosecond difference-frequency generation (DFG) source based on the new semiconductor nonlinear material, orientation-patterned gallium phosphide (OP-GaP). The DFG source is realized by mixing the output signal of a nanosecond OPO tunable over 1723-1827nm with the input pump pulses of the same OPO at 1064nm in an OP-GaP crystal, resulting in tunable generation over 233nm in the mid-infrared from 2548 to 2781nm. Using a 40-mm-long crystal, we have produced ∼14 mW of average DFG output power at 2719nm for a pump power of 5W and signal power of 1W at 80kHz repetition rate. To the best of our knowledge, this is the first single-pass nanosecond DFG source based on OP-GaP. The DFG output beam has a TEM00 spatial mode profile and exhibits passive power stability better than 1.7%rms over 1.4h at 2774nm, compared to 1.6% and 0.1%rms for the signal and pump, respectively. The OP-GaP crystal is recorded to have a temperature acceptance bandwidth of 17.7°C.

Angular non-critical phase-matching second-harmonic-generation characteristics of RECOB (RE = Tm, Y, Gd, Sm, Nd and La) crystals.

For the first time, the angular non-critical phase-matching (A-NCPM) second-harmonic-generation (SHG) characteristics of a family of monoclinic oxoborate crystals, RECa4O(BO3)3 (RECOB, RE = Tm, Y, Gd, Sm, Nd and La), were comprehensively investigated. For all of the realizable A-NCPM SHG styles, the feature parameters including PM wavelength, angular, wavelength and temperature acceptance bandwidths, have been derived from the theory and verified by the experiments. We discovered that the closer the ion radius between RE3+ and Ca2+, the smaller the birefringence, and the better the A-NCPM SHG properties. As a result, for the Type-I SHG on Y-axis which has the largest effective nonlinear optical coefficient (deff) among the three realizable A-NCPM styles, NdCOB crystal presents the longest PM wavelength (927 nm), the largest angular acceptance bandwidth (Δθ⋅l1/2 = 84.3 mrad·cm1/2, Δϕ⋅l1/2 = 58.8 mrad·cm1/2), and the broadest wavelength acceptance bandwidth (8.7 nm). This discovery will contribute to the design of new NCPM materials, at the same time the parameter formula will be helpful for the theoretical prediction of NCPM performance.

Temperature-insensitive quasi phase matching method for nonlinear frequency conversion

A temperature-insensitive quasi phase matching method is proposed to increase the temperature acceptance bandwidth in nonlinear optical frequency conversion. In the method, the nonlinear crystal is cut at an angle that enables the first temperature derivation of phase mismatching to be zero, which makes the phase mismatching value to be insensitive to temperature variation. Then, the phase velocities of mixing waves are quasi phase matched by appropriate poled period of the nonlinear crystal. Simulations of second harmonic generation of 1064nm in periodically poled KTiOPO4 crystal and 5mol% MgO-doped periodically poled LiNbO3 are conducted. The temperature acceptance bandwidths in periodically poled KTiOPO4 and 5mol% MgO-doped periodically poled LiNbO3 reach 943°Ccm and 393°Ccm, respectively.

Three-crystal method for thermally induced phase mismatch compensation in second-harmonic generation

A method capable of compensating the thermally induced phase mismatch in second-harmonic generation across a broad spectral range is proposed. Three nonlinear crystals are cascaded in a combination. The crystals at the two ends of the combination perform the frequency conversion. The middle crystal, with opposite sign of the first temperature derivative of phase mismatch, compensates the thermally induced phase mismatch in the first crystal. We theoretically demonstrate that the proposed method can be used to extend the temperature acceptance bandwidth for second-harmonic generation over a broad spectral range. And two examples are studied, frequency conversion from 1064 to 532 nm with Type II phase matching and 532 to 266 nm with Type I phase matching. The temperature acceptance bandwidth of the crystal combination is double that of a single crystal.

Improvement of the frequency-doubling efficiency of high-average-power lasers using multicrystal scheme with opposite thermal properties

Various multicrystal schemes have been widely used in the frequency conversion process of high power lasers or short-pulse lasers. Here we propose and numerically demonstrate a novel multicrystal scheme for improving the frequency-doubling efficiency of high-average-power lasers. Our proposed multicrystal scheme includes two different kinds of nonlinear crystals with opposite thermal properties, in which thermal-induced phase mismatches in the first crystal may be compensated by the next crystal. Asa result, the sensitivity of conversion efficiency to temperature deviations is reduced. The simulation results show that the temperature acceptance bandwidth of our two-crystal scheme is 5 times larger than that of common single crystal scheme. And a broader temperature acceptance bandwidth will be obtained if a three-crystal scheme is adopted. More important of all, the temperature-insensitive property of multicrystal scheme is independent of pump wavelength, which means it can be applied in various high-average-power laser systems.

Temperature-Insensitive Frequency Conversion by Electro-optic Effect Compensating for Phase Mismatch

A universal phase mismatch compensation method, which can be applied to temperature-insensitive frequency conversion, is experimentally demonstrated. In this method, two nonlinear crystals and an electro-optic crystal are cascaded. The generated phase mismatch in the nonlinear crystal can be well compensated for in the electro-optic crystal, thereby improving the stability of frequency conversion. In the proof-of-principle experiment, temperature-insensitive second and third harmonic generation (SHG and THG) are investigated by cascading KH2 PO4 (KDP) and KD2PO4 (DKDP) crystals. The experimental results show that the temperature acceptance bandwidths of SHG and THG are 2.1 and 2.3 times larger, respectively, than that of the traditional method employing a single crystal. Meanwhile, the effectiveness of this method is also analyzed at a high power density, and a solution for the case of a nonuniform temperature is also discussed. Furthermore, angle-insensitive SHG is demonstrated to prove that this method can significantly reduce the influence of various unfavorable factors on frequency conversion. The demonstrated method may have potentially important applications in the nonlinear optical frequency conversion system.

Fabrication of short-period poled structures and UV sum-frequency generation in 8 mol % MgO-doped congruent LiTaO3 crystal

Heavily (8 mol %) MgO-doped congruent LiTaO3 (MgO:cLT) crystal has wider transparency range and is expected to have higher photorefractive damage resistance than LiNbO3 or non-doped LT crystal. We obtained uniform PP structures with periods of ∼7 and ∼2 µm in MgO:cLT crystal and demonstrated UV sum-frequency generation (SFG) experiments at 355 nm wavelength for the first time. The FWHM temperature acceptance bandwidths and the normalized SFG efficiencies were close to the calculated values.

Compensation method for temperature-induced phase mismatch during frequency conversion in high-power laser systems

A compensation method for phase mismatch caused by temperature variation during the frequency conversion process is proposed and the theoretical model is established. The method is based on the principle that phase mismatch can be compensated via the electro-optic effect based on a compensation scheme consisting of two nonlinear crystals and an electro-optic crystal; further, a new dimension adjustment can be achieved by changing the voltage. In a proof-of-principle study, frequency conversion from 1053 nm to 526.5 nm and 351 nm by cascade KH2PO4 (KDP) and KD2PO4 (DKDP) crystals, respectively, is presented as an example. Three-dimensional numerical simulations are conducted to show that the conversion efficiency of frequency doubling and tripling varies with temperature. The results show that the temperature acceptance bandwidth of doubling and tripling can be 2.4 and 3.4 times larger, respectively, than that of the traditional method using a single crystal. We also analyze the stability of the conversion efficiency for 192 beams by our proposed method when the temperature is randomly varied within the range of 24°C–26°C. The standard deviation of the conversion efficiency of frequency doubling and tripling decreases from 1.25% and 6.61% to 0.18% and 0.56%, respectively. In addition, the influence of the reflection loss on the output efficiencies is also analyzed and the results show that it is very small. This indicates that this method may be effective in reducing the temperature sensitivity of conversion efficiency.

Continuous-wave single-frequency 589 nm yellow laser generated from sum frequency of single-block non-planar ring cavity laser in periodically poled KTiOPO4 crystal

Continuous-wave single-frequency 589 nm yellow laser can be used in laser cooling of sodium atoms. Besides, the interaction between 589 nm laser and sodium atoms can be studied by resonance fluorescence, which provides an important basis for the sodium guide star in the adaptive optics. In this paper, single frequency 589 nm yellow light is generated by sum frequency of single-block non-planar ring cavity 1064 nm and 1319 nm laser in periodically poled KTiOPO4 crystal. The geometric parameters of single-block non-planar Nd:YAG crystal and magnetic field intensity are optimally designed by simulation calculation through using Jones matrix. The output powers 1080 mW and 580 mW are obtained for continuous-wave single-frequency 1064 nm and 1319 nm laser in the experiment, respectively The two fundamental beams are expanded to be the same as perfectly as possible in size and are focused into a spot with a size of about 60 m by an achromatic lens. The sum-frequency generation takes place in a 1 mm2 mm20 mm phase-matched type-I periodically poled KTiOPO4 crystal with a matching temperature of 55℃ and polarization period of 12.35 m The crystal is anti-reflection coated for all three wavelengths (1064 nm, 1319 nm and 589 nm). A 14.8 mW output of 589 nm laser is obtained with beam quality factor M2=1.14 and the corresponding sum-frequency efficiency is 0.9%. The influence of periodically poled KTiOPO4 temperature on the sum-frequency efficiency is studied and the temperature acceptance bandwidth is measured to be 1.5 degrees The wavelength of 589 nm yellow light can be tuned to the sodium atom D2a absorption line by changing the temperature of 1064 nm Nd:YAG crystal and 0.164 pm of tuning accuracy is reached. The whole laser system is stable and reliable, so it provides a practical and effective technical means to obtain the continuous-wave single-frequency 589 nm laser, for it is relatively simple and easy to implement.

High-power, high-repetition-rate performance characteristics of β-BaB₂O₄ for single-pass picosecond ultraviolet generation at 266 nm.

We report a systematic study on the performance characteristics of a high-power, high-repetition-rate, picosecond ultraviolet (UV) source at 266 nm based on β-BaB2O4 (BBO). The source, based on single-pass fourth harmonic generation (FHG) of a compact Yb-fiber laser in a two-crystal spatial walk-off compensation scheme, generates up to 2.9 W of average power at 266 nm at a pulse repetition rate of ~80 MHz with a single-pass FHG efficiency of 35% from the green to UV. Detrimental issues such as thermal effects have been studied and confirmed by performing relevant measurements. Angular and temperature acceptance bandwidths in BBO for FHG to 266 nm are experimentally determined, indicating that the effective interaction length is limited by spatial walk-off and thermal gradients under high-power operation. The origin of dynamic color center formation due to two-photon absorption in BBO is investigated by measurements of intensity-dependent transmission at 266 nm. Using a suitable theoretical model, two-photon absorption coefficients as well as the color center densities have been estimated at different temperatures. The measurements show that the two-photon absorption coefficient in BBO at 266 nm is ~3.5 times lower at 200°C compared to that at room temperature. The long-term power stability as well as beam pointing stability is analyzed at different output power levels and focusing conditions. Using cylindrical optics, we have circularized the generated elliptic UV beam to a circularity of >90%. To our knowledge, this is the first time such high average powers and temperature-dependent two-photon absorption measurements at 266 nm are reported at repetition rates as high as ~80 MHz.