Noncritical Phase Matching Research Articles

Noncollinear third-harmonic generation with large angular acceptance by noncritical phase matching in KDP crystal.

The scheme of prefocusing to focus sum frequency generation (SFG) without a lens is proposed and experimentally verified in this study. Noncollinear type-I noncritical phase-matching SFG to generate a third-harmonic wave with large angular acceptance is presented. The principle of broad angular acceptance and the advantages of this PM configuration are also described in detail. External angular bandwidth of 7.33° for noncollinear SFG was measured in a 2 mm long KH2PO4 (KDP) crystal, which is in reasonably good agreement with the theoretical calculation. The mechanism of broadband SFG and the prefocusing scheme make it possible for the realization of convergent third-harmonic generation without involving a lens, which provides a promising way to avoid damage to optical components during the focusing of high-energy UV light in high-power laser facilities.

The effect of air flow on the temperature distribution and the harmonic conversion efficiency of the ADP crystal with large aperture in the temperature control scheme

This paper presented a temperature control scheme for ammonium dihydrogen phosphate (ADP) crystal of Ф80mm in diameter, and the influence of the air flow was also studied. This research aims to obtain the high energy, high frequency laser with large aperture under the non-critical phase matching (NCPM). Firstly, thermal analysis was carried out to investigate the air flow property in the cavity, as well as the effect of ambient temperature was analyzed. Secondly, the temperature distributions of air flow were achieved using the Finite Volume Method (FVM), and this prediction was validated by the experiment results. Finally, the effect of air flow in the cavity was obtained from the heating method, and the variation of harmonic conversion efficiency caused by the ambient temperature was also highlighted.

Noncritical phase matching fourth harmonic generation properties of KD(2)PO(4) crystals.

Noncritical phase matching (NCPM) fourth-harmonic-generation (FHG) experiments were conducted on different deuterium content DKDP crystals by adjusting crystal temperature to generate 266 nm deep UV laser. Specially, near room temperature NCPM is realized in extremely high deuterium content DKDP crystal at 38.6 °C, which is the lowest temperature to the best of our knowledge. NCPM temperature of DKDP crystals in 60-100% deuterium content range and 1050-1070 nm wavelength range are determined by a linear relationship according to the experimental and calculated results. Angular tuning properties are independent with deuterium content in medium and higher deuterium content DKDP crystals. All of these results will provide good references for future FHG applications of 1 μm laser with DKDP crystals.

The effects of structural parameter on the temperature distribution and conversion efficiency in the temperature control scheme of ADP squared crystal with large aperture

In order to obtain the best conversion efficiency of the laser with large diameter under the Non-Critical Phase Matching (NCPM), a temperature control scheme of ADP squared crystal with large aperture is proposed. The factors which influence the crystal temperature distribution are analyzed firstly, and the structural parameter is considered to be one of the most important factors. Then, the model of structural parameter is set up and studied by the Finite Volume Method (FVM) and experiment. Finally, the optimal parameter diameter is put forward and the temperature distribution of the ADP squared crystal is obtained, which caused the 2ω–4ω conversion efficiency is also studied by the FVM and experiment.

Low intensity noise and narrow line-width diode laser light at 540 nm

We present a convenient method to generate high quality single-frequency green light at a wavelength of 540 nm. It consists of a noise suppressed external cavity diode laser at a wavelength of 1080 nm by optical filtering and resonant optical feedback, and a frequency doubling of the fundamental light with an a-cut KTP crystal. Highly efficient conversion is realized by type II non-critical phase matching. A stable single-frequency operation with a maximum power of about 20 mW is performed for more than 3 h. Both the intensity noise and line-width reach the level of a monolithic nonplanar ring laser, which is well known for its extraordinarily narrow line-width and extremely low noise among available single-frequency operating lasers.

KTP OPO with signal wave at 1630 nm intracavity pumped by an efficient σ-polarized Nd,MgO:LiNbO_3 laser

An efficient, 808-nm-laser-diode end-pumped, σ-polarized Nd,MgO:LiNbO3 laser emitting at 1094 nm was demonstrated for the first time. The maximum output power of 1.49 W was obtained at the absorbed diode pump power of 6.48 W, corresponding to an optical-to-optical conversion efficiency of about 23%. The slope efficiency was approximately 25.7%. For applications, an intracavity optical parametric oscillator (IOPO) pumped by an actively Q-switched Nd,MgO:LiNbO3 laser with an acousto-optic modulator (AOM) was realized. An X-cut KTiOPO4 (KTP) worked as the nonlinear crystal for type II noncritical phase matching (NCPM). A maximum output power of the signal wavelength at 1630 nm was about 96 mW with a minimum pulse duration of 1.69 ns at an AOM repetition rate of 5 kHz, giving a peak power of 11.4 kW.

The influence of window thermal conductivity on the temperature distribution of the ADP crystal with large aperture

Motivated by the need of achieving the high frequency conversion efficiency of the laser beam with large diameter in the non-critical phase matching, a temperature control scheme of ADP crystal with large aperture was proposed. In this paper, in order to obtain the influence of the window thermal conductivity on the temperature distribution of ADP crystal, four different window materials, the thermal conductivities of which are different orders of magnitude, were proposed and analyzed by using the finite volume method (FVM) and experiments. The temperature distributions and temperature gradients of ADP crystal in the temperature control scheme with different window materials were discussed, and the optimal fourth harmonic generation (FHG) conversion efficiencies were obtained in different optics regions. Finally, the requirement of the window material thermal conductivity was proposed in order to obtain the high frequency conversion efficiency.

Blue light production by type-I non-critical phase matching second-harmonic generation in La(Ca1−xSrx)4O(BO3)3single crystals

The optical birefringence of La(Ca1−xSrx)4O(BO3)3 nonlinear optical crystals can be controlled by changing the compositional parameter x. Therefore, it is possible to achieve non-critical phase matching (NCPM) for type-I second-harmonic generation (SHG) of specific wavelengths in the range of 990 to at least 946 nm. La(Ca1−xSrx)4O(BO3)3 single crystals (with x = 0.0, 0.1, 0.3 and 0.4 starting compositions) of large size and good optical quality were grown by the Czochralski method. X-ray diffraction measurements have been carried out to characterize the structural changes with compositional parameters x. The NCPM wavelengths along the Z-axis were experimentally determined for each grown crystal. According to our assumptions, the obtained results demonstrate that by an appropriate choice of the compositional parameter x in La(Ca1−xSrx)4O(BO3)3 crystals, we can obtain blue light in the range of 495–473 nm through type-I NCPM SHG of the corresponding fundamental wavelengths, which are very attractive for practical applications.

Rapid growth of a large size, highly deuterated DKDP crystal and its efficient noncritical phase matching fourth-harmonic-generation of a Nd:YAG laser

Large size DKDP crystal with high and homogenous deuterium content contributes to efficient noncritical phase matching FHG of ND:YAG laser.

Phase matching characteristics of deuterated ammonium dihydrogen phosphate crystals

Refractive indices for crystals ammonium dihydrogen phosphate (ADP), 30% deuterated ADP (DADP), 50% DADP, and 70% DADP are measured from 253 to 1529 nm with 5 × 10-6 accuracy. Numerical fits to modified double-pole Sellmeier equation are made. Second-harmonic generation, third-harmonic generation phase matching (PM) angles, and noncritical PM (NCPM) wavelengths are calculated using the Sellmeier parameters. The deuterated crystals show smaller PM angles than pure crystal. Fourth-harmonic generation process can be realized by DADP in smaller deuterium content than deuterated potassium dihydrogen phosphate (DKDP). The measured NCPM wavelengths are consistent with the calculated value. PM characteristics are compared between DADP and DKDP.

Compact Nd:YAlO$_{3}$/RbTiOPO $_{4}$ Based Intra-Cavity Optical Parametric Oscillator Emit at 1.65 and 3.13 μm

An intra-cavity optical parametric oscillator based on RbTiOPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> (RTP) crystal simultaneous output eye-safe light and mid-infrared wavelength light was demonstrated. An laser diode end pumped acousto-optic Q-switched Nd:YAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> laser at 1.08 μm was used as the pump source. At an incident pump power of 8.7 W and a pulse repetition frequency of 20 kHz, total average output power up to 1.12 W (890 mW of signal light at 1.65 μm with and 230 mW of idler light at 3.13 μm) was obtained, with the diode to OPO total output conversion efficiency of 12.9%. The pulse width is about 4.5 ns and spectral linewidth is about 0.5 nm for the signal light. Compare to noncritical phase matching optical parametric oscillator using its isomorph KTP crystal, RTP crystal can extend signal wavelength up to 1.65 μm and absorb less idler wavelength.

Mechanical phase matching of birefringent non-linear crystals.

Second-order nonlinear processes such as second harmonic generation or parametric amplification have found numerous applications in the scientific and industrial world, from micromachining to petawatt laser facilities. These nonlinear interactions are mostly carried out in birefringent crystals because of their low cost and the possibility to operate at high powers Phase-matching configurations in birefringent crystals are determined by their refractive indexes. Here, we show that an important mechanical stress can be used to significantly change the phase-matching properties of a birefringent crystal. As an example, we demonstrate the shift of second harmonic non-critical phase matching wavelength of LiB3O5 (LBO) crystal at room temperature from 1200 nm to 1120 nm by applying compressive forces up to 100 MPa. We believe that this mechanical phase matching can be used as an additional degree of freedom to optimize nonlinear optical frequency mixing geometries.

Anisotropy of nonlinear optical properties in monoclinic crystal TmCa_4O(BO_3)_3

New nonlinear optical (NLO) crystals TmCa4O(BO3)3 (TmCOB) were grown by the Czochralski pulling method, and the anisotropy of second-harmonic-generation (SHG) properties were characterized. Based on the ratio of the peaks of the 2ω signals produced by TmCOB and that of KTP crystal samples at the low fundamental energy, the NLO tensor coefficients d12, d32, d31 and d13 were determined and found to be 0.24, 1.70, −0.55 and −0.32 pm/V, respectively. At 1064 nm, the phase-matching (PM) curves and the effective NLO coefficients (deff) in spatial distribution were evaluated. Efficient SHG was realized on a (32.5°, 180°)-cut TmCOB sample (4 × 4 × 11.8 mm3) in principal plane, by using a 1064 nm Nd:YAG pico-second laser, where the highest conversion efficiency of the single-pass light reached up to 51%, while for a (112.5°, 35.9°)-cut TmCOB sample (4 × 4 × 8 mm3) in spatial PM direction, the single-pass light reached 58%. Meanwhile, the angular noncritical phase matching (A-NCPM) wavelengths along the Y and Z principal axes were calculated and measured, and the limit of type-I PM wavelength of TmCOB was found to be 716 nm.

Efficient RTP-based OPO intracavity pumped by an acousto-optic Q-switched Nd:YVO_4 laser

This Letter describes an intracavity pumped optical parametric oscillator (OPO) based on noncritical phase matching RbTiOPO4 (RTP) crystal driven by a laser diode end-pumping acousto-optic Q-switched Nd:YVO4 laser. Simultaneous efficient signal light at 1.6 μm and idler light at 3.1 μm outputs were obtained. At an incident pump power of 10.5 W and a Q-switching pulse repetition frequency of 60 kHz, 1.42 W at center wavelength of about 1619 nm and 0.38 W at 3108 nm were achieved, with the diode to OPO total output conversion efficiency up to 17.1%. The pulse width is about 6.5 ns for the signal light corresponding to the fundamental light at 1064 nm of about 10 ns. The spectral widths of the signal and idler light are narrower than 0.5 and 1.0 nm. The result shows that the RTP crystal is an efficient crystal to generate eye-safe and mid-infrared lights by making full use of noncritical phase matching.

非临界相位匹配RTP晶体1.6 μm光参量振荡器

非临界相位匹配RTP晶体1.6 μm光参量振荡器

Refractive indices in the whole transmission range of partially deuterated KDP crystals

Refractive indices of partially deuterated potassium dihydrogen phosphate (DKDP) crystals with 55%, 70% and 80% deuterium contents were measured by auto-collimation method at 293 K between 0.254 to 1.529 μm. Dependence of refractive indices of DKDP on deuterium content show different trend in the infrared region as in uv-visible region. Dependence of n2 (the square of refractive index) on the mole fraction of deuterium shows a difference between pure KDP and partially deuterated KDP. The Sellmeier equations were obtained by the least square method. The non-critical phase matching angles calculated from the fitted formula were in good agreement with laser experiment results, by which the reliability of these Sellmeier equations was confirmed.

Non-critical phase-matching fourth harmonic generation of a 1053-nm laser in an ADP crystal

In current inertial confinement fusion (ICF) facilities, KDP and DKDP crystals are the second harmonic generation (SHG) and third harmonic generation (THG) materials for the Nd:glass laser (1053 nm). Based on the trend for the development of short wavelengths for ICF driving lasers, technical solutions for fourth harmonic generation (FHG) will undoubtedly attract more and more attention. In this paper, the rapid growth of an ADP crystal and non-critical phase-matching (NCPM) FHG of a 1053-nm laser using an ADP crystal are reported. The NCPM temperature is 33.7°C. The conversion efficiency from 526 to 263 nm is 70%, and the angular acceptance range is 55.4 mrad; these results are superior to those for the DKDP crystals. This research has shown that ADP crystals will be a competitive candidate in future ICF facilities when the utilisation of high-energy, high-efficiency UV lasers at wavelengths shorter than the present 351 nm is of interest.

Generation of 2-$\mu{\rm m}$ Light Based on a Noncritical Phase Matching OPO Technique

We propose an experimental technique for efficient 2- μm light generation based on the intracavity noncritical phase matching optical parametric oscillator (OPO). Intra-cavity pumped by a diode pumped actively Q-switched Nd:YVO4 laser operating at 1.3 μm, we have achieved efficient 2093-nm signal beam emission making full use of noncritical phase matching KTA-OPO. At a diode pump power of 9.8 W and a Q-switching repetition rate of 30 kHz, a signal beam with a spectral linewidth of ~ 1 nm and an average power of 1.01 W have been obtained, giving a diode pump power to signal power conversion efficiency of 10.3%. The short pulse width of ~ 3.4 ns is achieved, which is much shorter than other approaches with Q-switched operation to generate 2-μm laser beams.

新型非临界相位匹配KTA-OPO 2 μm激光器

新型非临界相位匹配KTA-OPO 2 μm激光器

Efficient Second Harmonic Generation Of Blue-Violet Light In Noncritical Type-I Phase Matching

Abstract Single crystals of Y1−xRxCa4O(BO3)3 (R = Sc or Lu) of good quality have been grown from the melt by the Czochralski pulling method. The chemical compositions of the grown crystals were determined. Type-I noncritical phase matching (NCPM) wavelengths for second harmonic generation (SHG) in Y1−xRxCa4O(BO3)3 grown crystals were also determined.