KTP Optical Parametric Oscillator Research Articles

High-efficiency narrow-bandwidth KTP optical parametric oscillator for kHz-MHz planar laser-induced fluorescence.

The electronic excitation of key combustion species or flow tagging of chemical species requires a narrowband tunable UV source. In this work, a potassium titanyl phosphate (KTP) burst-mode optical parametric oscillator (OPO) pumped by a 532 nm laser is developed to generate a spectrally narrow signal and an idler output with 1.48 ± 0.19 cm-1 bandwidth without the need for injection seeding. The idler (1410-1550 nm range) is further mixed with 355 or 266 nm to generate 284 or 226 nm for OH or NO planar laser-induced fluorescence (PLIF), respectively, with up to 1.9% conversion efficiency from 1064 nm to the UV. MHz-rate burst profiles are reported, and OH and NO PLIF are demonstrated in a rotating detonation combustor at rates up to 200 kHz.

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.

Self-Cascaded Noncritically-Phase-Matched Ktp Optical Parametric Oscillator for Generating Orthogonally Polarized Multi-Wavelength Emissions at 3 Μm

Self-Cascaded Noncritically-Phase-Matched Ktp Optical Parametric Oscillator for Generating Orthogonally Polarized Multi-Wavelength Emissions at 3 Μm

High average power 200 fs mid-infrared KTP optical parametric oscillator tunable from 2.61 to 3.84 μm

High average power 200 fs mid-infrared KTP optical parametric oscillator tunable from 2.61 to 3.84 μm

Widely tunable eye-safe optical parametric oscillator with noncollinear phase-matching in a ring cavity.

An effective method for wavelength tuning in an optical parametric oscillator (OPO) was proposed using noncollinear phase-matching (PM) in a ring cavity. This method was particularly useful for noncritically phase-matched (NCPM) KTP/KTA OPOs where changing the crystal orientation or working temperature is ineffective. A wide tuning range in the eye-safe band from 1572.9 nm to 1684.2 nm was realized pumped by an Nd:YAG laser at 1.06 μm in an NCPM KTP OPO while the internal noncollinear angle was tuned from 0 to 3.1° or the external angle from 0° to 5.8°, with slight variation of the deflection angle of one cavity mirror. The good beam quality and high spectrum intensity of the narrow-linewidth Nd:YAG laser resulted in 33.3% conversion efficiency for the collinear case and above 11% throughout the tuning range. Such OPOs have many potential applications where tunable eye-safe lasers are required, and the proposed wavelength tuning method can be extended to all kinds of OPOs.

4.5 kW peak power 2958 nm gain-switched Ho, Pr:LLF laser pumped by KTP optical parametric oscillator

With the pump of a KTP optical parametric oscillator (OPO) at 1150 nm, a gain-switched Ho,Pr:LLF laser was experimentally demonstrated in this paper. The maximum single pulse energy of 98.8 μJ with the minimum pulse width of 22 ns was achieved at the pulse repetition frequency (PRF) of 1 Hz, corresponding to a peak power of 4.5 kW. The central wavelength of the gain-switched laser was 2958 nm with a full width at half maximum (FWHM) of 4.5 nm.

High-repetition-rate, tunable and coherent mid-infrared source based on difference frequency generation from a dual-wavelength 2 µm laser and GaSe crystal

Although high-repetition-rate dual-wavelength 2 µm KTP optical parametric oscillators (OPOs) have been realized for quite a long time, we have treated one in generating coherent mid-infrared waves in this paper for the first time. The dual-wavelength 2 µm laser is generated from a KTP OPO intracavity, pumped by an acousto-optically Q-switched side-pumped Nd:YAG laser. Treating an 8 mm long GaSe crystal for difference frequency generation (DFG), a maximum average output power of 360 µW is obtained at a pulse-repetition rate of 10 kHz at the wavelength of 9.6 µm for type-I phase matching DFG. The peak power amounts to 3.3 W and the conversion efficiency is 0.12%. The continuously tunable and coherent radiation in the mid-infrared range of 9–16 µm has been achieved. Moreover, type-II phase matching DFG with an output wavelength continuously tunable in the range of 9–13.7 µm has also been achieved. The output mid-infrared power scaling is still feasible with a higher pump power and a nonlinear DFG crystal with a higher damage threshold.

Investigation of Adhesive-free bonded Potassium Titanyl Phosphate crystal based optical parametric oscillator for generation of 2.1 µm wavelength at high repetition rate

In this paper an application of newly available adhesive-free bonded Potassium Titanyl Phosphate crystal is reported. An optical parametric oscillator (OPO) based on a pair of adhesive-free bonded (AFB) Potassium Titanyl Phosphate (KTP) crystals in a walk-off compensated configuration has been demonstrated and investigated. A maximum average output power of 3 W has been achieved at a pulse repetition rate of 10 KHz using Nd:YVO4 as a pump source. The OPO generates near degenerate wavelengths at 2.127 µm and 2.131 µm with a small spectral separation of 4 nm. The results show a highly stable output with a slope efficiency of 23.6% and OPO threshold as low as 32 MW/cm2. The OPO output stability and threshold achieved is significantly better as compared to conventional KTP OPO.

Compact, efficient and widely tunable 2-[formula omitted]m high-repetition-rate optical parametric oscillators

Compact efficient high-repetition-rate tunable optical parametric oscillators (OPOs) in the 2-μm region were investigated, based on nonlinear crystals of KTP and periodically polarized LiNbO3 (PPLN) intracavity pumped by a diode-end-pumped acousto-optical (AO) Q-switched Nd:YVO4 laser. The cavity was designed and optimized from the theoretically analysis on thermal stability and mode matching. Using walk-off compensated twin KTP-crystal pairs as the nonlinear media, the maximum output power of 4.15 W was obtained at 25 kHz and the tuning range spanned from 1923.22 nm to 2378.63 nm, pumped at the diode power of 18.41 W at 808 nm. The optical–optical conversion efficiency of 22.5% and the photon conversion efficiency of around 60% are both among the highest in intracavity pumped OPOs. To overcome the power degradation during angle tuning, a type-II quasi-phase matched (QPM) PPLN crystal with temperature tuning was also studied. With a 55-mm-long 14.1-μm-grating period PPLN crystal, the maximum output power was 3.41 W corresponding to the optical–optical conversion efficiency of 18.5%. Both the KTP and PPLN OPOs demonstrated good efficiency as well as temporal, spectrum and beam characteristics, providing excellent 2-μm laser source for applications of lidar, medical diagnosis, nonlinear frequency conversion to the long-wave infrared and terahertz range, etc.

High-average-power, high-repetition-rate tunable terahertz difference frequency generation with GaSe crystal pumped by 2 μm dual-wavelength intracavity KTP optical parametric oscillator

We have demonstrated a high-average-power, high-repetition-rate optical terahertz (THz) source based on difference frequency generation (DFG) in the GaSe crystal by using a near-degenerate 2 μm intracavity KTP optical parametric oscillator as the pump source. The power of the 2 μm dual-wavelength laser was up to 12.33 W with continuous tuning ranges of 1988.0–2196.2 nm/2278.4–2065.6 nm for two waves. Different GaSe cystal lengths have been experimentally investigated for the DFG THz source in order to optimize the THz output power, which was in good agreement with the theoretical analysis. Based on an 8 mm long GaSe crystal, the THz wave was continuously tuned from 0.21 to 3 THz. The maximum THz average power of 1.66 μW was obtained at repetition rate of 10 kHz under 1.48 THz. The single pulse energy amounted to 166 pJ and the conversion efficiency from 2 μm laser to THz output was 1.68×10−6. The signal-to-noise ratio of the detected THz voltage was 23 dB. The acceptance angle of DFG in the GaSe crystal was measured to be 0.16°.

High power, widely tunable dual-wavelength 2 μm laser based on intracavity KTP optical parametric oscillator

We presented a high power, widely tunable narrowband 2 μm dual-wavelength source employing intracavity optical parametric oscillator with potassium titanium oxide phosphate (KTP) crystal. Two identical KTP crystals were oriented oppositely in the OPO cavity to compensate the walk-off effect. The output average power of dual-wavelength 2 μm laser was up to 18.18 W at 10 kHz with the peak power of 165 kW. The two wavelengths can be tuned in the range of 2070.7 nm to 2191.1 nm for ordinary light while in the range of 2190.7 nm to 2065.9 nm for extraordinary light with the full width at half maximum (FWHM) about 0.8 nm. The pulse width of the tunable laser was as narrow as 11 ns. The beam quality factor M2 was less than 4 during wavelength tuning.

Widely-tunable high-repetition-rate terahertz generation in GaSe with a compact dual-wavelength KTP OPO around 2 μm.

A compact efficient high-repetition-rate doubly-resonant dual-wavelength KTP optical parametric oscillator (OPO), with output power up to 3.65 W and tuning ranges of 2.088-2.133 μm/2.171-2.122 μm for signal/idler waves, was deployed for terahertz (THz) generation in a GaSe crystal. Based on difference frequency generation (DFG), the THz wave was continuously tunable from 730.9 μm (0.41 THz) to 80.8 μm (3.71 THz), believed to be the first report of a compact high-repetition-rate widely-tunable THz source. The maximum THz average power reached 1.2 μW at 1.54 THz and the corresponding DFG efficiency was 7.8 × 10-7, entirely suitable for portable applications. The utility of the THz source was also demonstrated through spectroscopy and imaging experiments.

Simultaneous dual-wavelength eye-safe KTP OPO intracavity pumped by a Nd:GYSGG laser

A simultaneous dual-wavelength intracavity pumped non-critical eye-safe optical parametric oscillator (OPO) is realized using a Nd:GYSGG laser crystal and a KTP nonlinear crystal. A folded cavity is used for thermal stability and mode matching, which greatly improves the output characteristics versus a linear cavity. The maximum output power of the 1562.1 nm/1567.4 nm dual-wavelength eye-safe laser is 750 mW at 10 kHz, corresponding to the optical-to-optical conversion efficiency, single-pulse-energy and peak power of 5.8%, 75 μJ and 22.7 kW. Such a dual-wavelength OPO provides a good laser source for remote sensing for CO and CO2 gases or difference frequency generation for terahertz wave at the important 0.65 THz band.

High average-power 2 μm radiation generated by intracavity KTP OPO

A high average-power 2 μm laser with good beam quality based on an intracavity potassium titanium oxide phosphate (KTP) optical parametric oscillator (OPO) is demonstrated. A concave lens is used in the 1064 nm Nd:YAG pumped laser cavity to compensate for the thermal lensing of the laser rod. The cavity length of the KTP OPO is enlarged to improve the 2 μm beam quality. The maximum average output of the 2 μm laser is up to 18 W at 7 kHz with M2 less than 6 and pulse width of 70 ns. The FWHM of the signal and idle lights are both less than 3 nm.

Efficient high-peak-power and high-repetition-rate eye-safe laser using an intracavity KTP OPO

An efficient high-peak-power and high-repetition-rate intracavity KTP optical parametric oscillator pumped by a Q-switched Nd:YVO4 laser is demonstrated. We achieved 1.5 W output power of 1.5 μm at 10 kHz repetition rate with the pulse duration of 6 ns. The maximum peak power of 25 kW and the maximum pulse energy of 150 μJ have been obtained. The maximum conversion efficiency of 9.5% is achieved with respect to a laser diode power of 10.5 W.

Growth of low etch pit density ZnGeP2 crystals by the modified vertical Bridgman method

Based on the high-quality polycrystalline ZnGeP2 (ZGP) synthesized by the optimized two-temperature-zone method, ZnGeP2 single crystals with dimensions of 16mm diameter and 70mm length were successfully grown using the modified vertical Bridgman method. The etch pit density (EPD) of as-growth crystals can be reduced to a level of 510cm−2; the full width at half maximum (FWHM) of the X-ray rocking curve of the crystals is 20″; the transmittance of the annealed and polished wafers (1.7mm thick) can reach about 57% in the wavelength range 3–8µm and the optical absorption coefficient is about 0.1cm−1 at 2.1µm; using KTP optical parametric oscillator (OPO) pumping source at 2.1µm, the output power of ZGP OPO is 2.8W at 3–5µm. These results suggest that this modified vertical Bridgman method can grow high structural and optical quality ZGP single crystals for OPOs.

种子注入环形腔人眼安全KTP参变振荡器的研究

种子注入环形腔人眼安全KTP参变振荡器的研究

Mid-infrared optical parametric oscillator based on ZnGeP2 pumped by 2- \mum laser

We present a 3~5 μm optical parametric oscillator (OPO) based on ZGP pumped by KTP OPO 2.1-μm laser. The tuning curves of ZGP OPO are calculated. The x 6 x 18 (mm) ZGP crystal, whose end faces are antireflection coated at 2.1 and 3.7~4.6 μm, is cut as Θ =53.5o, Φ =0o. When the pump power of 2.1-μm polarized laser is 15 W at 8 kHz, 5.7-W output power and 46.6% slope efficiency are obtained with a ZGPtype I phase match. Central wavelengths of the signal and idler lasers are 4.10 and 4.32 μm, respectively. Pulse duration is about 27 ns. Beam quality factor M2 is better than 1.8. The tunability of 3~5 μm can be achieved by changing the angle of the ZGP crystal.

Dual-wavelength single-crystal double-pass KTP optical parametric oscillator and its application in terahertz wave generation

A tunable dual-wavelength double-pass singly resonant optical parametric oscillator based on a single KTP crystal has been proposed and demonstrated. By setting the rear mirror tuning angle precisely, collinear and noncollinear dual phase matching can be established simultaneously and leads to a two-wavelength oscillation at steady state. With high-speed KTP angle tuning, two wavelengths and their frequency difference can be adjusted continuously and accurately. By using this newly developed dual-wavelength optical parametric oscillator to pump a DAST crystal, a monochromatic terahertz wave ranging from 0.5 to 3 THz has been successfully generated in a difference-frequency generation system.

Tunable and coherent nanosecond 7.2–12.2 μm mid-infrared generation based on difference frequency mixing in ZnGeP2 crystal

A coherent mid-infrared laser source, which can be tuned from 7.2 μm to 12.2 μm based on the type-II phase-matched difference frequency generation (DFG) in an uncoated ZnGeP2 (ZGP) crystal, is reported. The two pump waves are from a type-II phase-matched dual-wavelength KTP optical parametric oscillator (OPO) of which the signal and idler waves are tuned during 1.85–1.96 μm (extraordinary wave) and 2.5–2.33 μm (ordinary wave), respectively. The maximum energy of the generated mid-infrared laser is 10 μJ at 9.22 μm, corresponding to the peak power of 2.2 kW.