Mid-infrared ZGP OPO pumped by near-degenerate narrowband type-I PPKTP parametric oscillator

The total pulse energy of the signal and idler in a near-degenerate type-I periodically poled KTiOPO₄ (PPKTP) optical parametrical oscillator (OPO) was spectrally confined within a 2 nm spectral bandwidth at 2.13 μm. This was achieved by using a volume Bragg grating as the output coupler. Both the signal and the idler from the PPKTP OPO were then simultaneously used to pump a mid-infrared ZnGeP₂ (ZGP) OPO. The 2 nm bandwidth was narrower than the ZGP crystal acceptance bandwidth and, thus, made efficient conversion in the second OPO possible. A total slope efficiency of 10% from 1.06 μm to the 3.5–5 μm region was demonstrated, generating 250 μJ in the mid-IR with only 3.6 mJ of 1.06 μm pump energy. This corresponds to a Nd:YAG pump to mid-IR conversion efficiency of 7%. PACS 42.65.Yj; 42.72.Ai; 42.40.Eq     

A ring ZnGeP2 optical parametric oscillator pumped by a Ho:LuAG laser

We have demonstrated that we believe to be the first ring ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a pulsed Ho:LuAG laser. The maximum output power of the ring ZGP OPO laser was 5.51 W at 13.1 W incident Ho pump power, corresponding to a slope efficiency of 59.0 %. The ZGP OPO laser produced 14 ns mid-infrared pulses in the 3.72–4.01 and 4.37–4.75 μm spectral regions simultaneously. In addition, the continuous wave Ho:LuAG laser generated 26.5 W of linearly output at 2,094.4 nm at the absorbed Tm pump power of 49.9 W.     

A High-Power,Long-Wavelength Infrared ZnGeP<Subscript>2</Subscript> Opo Pumped by a <Emphasis Type="Italic">Q</Emphasis>-Switched Tm,Ho:GdVO<Subscript>4</Subscript> Laser

We report a high-power, long-wavelength infrared ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a Q-switched Tm,Ho:GdVO₄ laser. The wavelength tuning range of 7.8–9.9 μm is realized by rotating the external angle of the ZGP crystal. We obtain an output power over 30 mW across the whole wavelength range and achieve a 1.71 W output power at 8.08 μm by transmitting the OPO parameters, corresponding to an idler laser slope efficiency of 12.1%.     

Mid-infrared tunable dual-wavelength generation based on a quasi-phase-matched optical parametric oscillator

We report an efficient optical parametric oscillator (OPO) of dual idler wave output based on periodically poled MgO:LiNbO₃ with a periodically-phase-reversed grating structure, which is pumped by a Q-switched 1.064 μm laser with a repetition rate of 50 kHz. 0.98 W of dual idler-waves at 3.824 μm and 3.731 μm is achieved at room temperature, leading to a 12.9% conversion efficiency. The crystal temperature tuning provides output tunability of the dual idler wavelengths. In addition, the sum frequency generation of the dual signal waves is simultaneously observed in the OPO cavity.     

High-power,high-quality ZGP OPO pumped by a Tm,Ho:GdVO<Subscript>4</Subscript> laser

We report a ZGP OPO system capable of producing >6 W at a signal wavelength of 3.80 μm and an idler wavelength of 4.45 μm. The pumping source is the Tm,Ho:GdVO₄ laser operated at 2.049 μm with an M ² of 1.07. The ZGP OPO generated a total combined output power of 6.1 W at signal wavelength and idler wavelength under pumping power of 18.3 W, and an M ² of 1.7 for OPO output was obtained.     

Pump tuned wide tunable noncritically phase-matched ZnGeP2 narrow line width optical parametric oscillator

A line tunable singly resonant noncritically phase matched narrow band width ZnGeP₂ (ZGP) optical parametric oscillator pumped by the output idler radiation from a KTA OPO based on a 20 mm long KTA crystal pumped from a Q-switched Gaussian shaped Nd:YAG laser beam with a grating having grooves density 85 lines/mm has been demonstrated in the spectral ranges of 3–7 μm. The measured threshold of oscillation energy was 10 μJ. The conversion efficiency was 20.5% and slope efficiency of the ZGP OPO was 20% using a 23 mm long ZGP crystal at 26 mm cavity length. Line width of the generated infrared radiation from ZGP OPO was 37–60 nm.     

Performance evaluation of ZnGeP2 optical parametric oscillator pumped by a Q-switched Tm,Ho:GdVO4 laser

A doubly resonant ZnGeP2 （ZGP） optical parametric oscillator （OPO） pumped by a novel Tm,Ho：GdVO4 laser was demonstrated. Cryogenic Tin（5 at.-%）, Ho（0.5 at.-%）：GdVO4 laser with high pulse repetition frequency （PRF） of 10 kHz at 2.05 μm was employed as pumping source of ZGP OPO. The 15-mm-long ZGP crystal, 55° cut for I-type phase-matching with low absorption coefficient less than 0.05 cm^-1 at 2 μm, was placed in a piano-piano cavity with resonator length of 30 mm. The ZGP OPO generated a total combined output power of 1.2 W at 3.75 and 4.52 μm under pumping power of 5.3 W, corresponding to slope efficiency of 40% from incident 2μm laser power to midinfrared （Mid-IR） output. A widely tunable range from 3.0 to 6.5 μm was achieved by changing the crystal angle only 3.5°.     

Low-pump-threshold tunable optical parametric oscillator using periodically poled MgO:LiNbO3

We fabricated and characterized periodically poled MgO:LiNbO₃ device with five gratings in 0.5 μm increments from 29 μm to 31 μm for optical parametric oscillator (OPO). The OPO operation threshold is 30 μJ using this device with a 50 mm effective length. At 560 mW input pump power, we have achieved 300 mW of the total output power, and the conversion efficiency is 54%. Multi-periods and temperatures tuning of the OPO yields a signal wavelength range from 1.45 to 1.72 μm and an idler wavelength range from 2.8 to 4.05 μm in the mid infrared.     

High efficiency and high energy parametric wavelength conversion using a large aperture periodically poled MgO:LiNbO3

We have demonstrated an efficient high energy 2 μm laser generation with a 36 mm long large aperture 5 mol% MgO-doped periodically poled LiNbO₃ (PPMgLN) nonlinear optical crystal. A high power Q-switched Nd:YAG laser (1.064 μm) was used to pump the quasi-phase matched (QPM) optical parametric oscillator (OPO). A total output energy of 186 mJ with 58% slope efficiency was obtained in two separate beams at 2 μm.     

Comparative investigation of long-wave infrared generation based on ZnGeP2 and CdSe optical parametric oscillators

Long-wave infrared (IR) generation based on type-II (o→e+o) phase matching ZnGeP₂ (ZGP) and CdSe optical parametric oscillators (OPOs) pumped by a 2.05 μm Tm,Ho:GdVO₄ laser is reported. The comparisons of the birefringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally. For the ZGP OPO, up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency (PRF) with a slope efficiency of 7.6%. This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm. For the CdSe OPO, we demonstrate a 64 mW output at 8.9 μm with a single crystal 28 mm in length.     

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

We present a 3 5 μ m optical parametric oscillator (OPO) based on ZGP pumped by KTP OPO 2.1-μ m laser. The tuning curves of ZGP OPO are calculated. The 8 ×6 ×18 (mm) ZGP crystal, whose end faces are antireflection coated at 2.1 and 3.7 4.6 μ m, is cut as θ =53.5°, φ =0°. When the pump power of 2.1-μ m polarized laser is 15 W at 8 kHz, 5.7-W output power and 46.6% slope efficiency are obtained with a ZGP type I phase match. Central wavelengths of the signal and idler lasers are 4.10 and 4.32 μ m, respectively. Pulse duration is about 27 ns. Beam quality factor M 2 is better than 1.8. The tunability of 3 5 μ m can be achieved by changing the angle of the ZGP crystal.     

High repetition rate mid-infrared generation with singly resonant optical parametric oscillator using multi-grating periodically poled MgO:LiNbO3

A high repetition rate mid-infrared singly resonant optical parametric oscillator (OPO) using MgO-doped multi-grating periodically poled LiNbO₃ (MgO:PPLN) is demonstrated. A 1064 nm Q-switched Nd:YVO₄ laser at 10 kHz repetition rate and pulse width of 17.8 ns was used to pump the OPO. The period of the quasi-phase matched (QPM) grating in the multi-grating MgO:PPLN chip varied from 25.5 to 31.5 μm in steps of 0.5 μm. This corresponds to the generation of a signal beam from 1.37 to 1.64 μm and an idler beam from 3.0 to 4.8 μm, respectively. A maximum signal power of 250 mW and idler power of 140 mW has been obtained with an input pump beam of power 1.92 W, for a grating period of 30.5 μm. A maximum optic-optic conversion efficiency of 20% and 7.4% in the idler has been observed. It has been observed that the output power increases as the period of the grating increases.     

Widely tunable, high-repetition-rate, dual signal-wave optical parametric oscillator by using two periodically poled crystals

This paper reports on a high-repetition-rate dual signal-wave (DSW) optical parametric oscillator (OPO) operating at the 1.5 μm band with tunable wavelength intervals from 2.5 nm to 69.1 nm. Two periodically poled crystals, a periodically poled lithium niobate (PPLN) with multiple gratings and a single grating MgO-doped PPLN (PPMgOLN), are cascaded in the same OPO cavity to generate dual signal-waves by using quasi-phase-matched (QPM) technique. The pump source was a Q-switched diode-pumped Nd:YVO₄ laser operating at 50 kHz. At an incident pump power of 3 W, an average output power of 169.6 mW at 1489.2 nm and 1558.3 nm has been achieved.     

Wavelength-agile mid-infrared (5-10 microm) generation using a galvano-controlled KTiOPO4 optical parametric oscillator

A wavelength-agile mid-infrared (IR) ZnGeP2 (ZGP) optical parametric oscillator (OPO) using a galvano-controlled double-crystal KTiOPO4 (KTP) OPO was demonstrated. The mid-IR wavelength was tuned by varying the KTP OPO pump wavelength while the ZGP crystal angle remained fixed. Rapid tuning of the KTP OPO was achieved by changing the crystal angle by using the galvano scanner. Our mid-IR source can jump to a different wavelength without scanning through the intermediate wavelengths while also permitting continuous-wavelength scanning. The mid-IR source can be tuned from approximately 5to10 microm at a phase-matching angle of 51 degrees , while the pump wavelength is controlled in the 1.95-2.2 microm range.     

磷锗锌光学参量振荡器技术研究

 报道了一台高重复频率2 mm光学参量振荡器泵浦的磷锗锌光学参量振荡器。磷锗锌晶体(ZnGeP₂,简称ZGP)采用Ⅰ类相位匹配方式,切割角度q为55°,f为0°,尺寸5.5 mm×6 mm×18 mm,在4.0 kHz重复频率下,当注入5.2 W的2 mm圆偏振光时,获得310 mW中红外输出,p偏振态2 mm到3～5 mm光-光转换效率12%。通过调节晶体的角度,实验获得ZGP光学参量振荡器的波长调谐曲线,在误差范围内与理论变化规律相符。     

Tunable, high-power, narrow-band picosecond IR radiation by optical parametric amplification in KTP

We report on an optical parametric amplifier (OPA) based on two potassium titanyl phosphate (KTP) crystals in a walk-off compensating geometry. An Nd:YLF regenerative amplifier at a 1-kHz repetition rate serves as the pump source. The seed beam is delivered by a synchronously pumped frequency-stabilized optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN). At pump intensities of about 7 GW/cm² large amplification factors of more than 10⁴ were achieved, resulting in pulse energies of more than 450 μJ and 350 μJ for the signal and idler pulses, respectively, at a 1-kHz repetition rate. In the saturation regime the time–bandwidth product increases from two to three times the Fourier limit, with a pulse duration of 105 ps and a bandwidth of 12.7 GHz at the highest intensities employed. Received: 2 November 2001 / Published online: 14 March 2002     

Gaussian- versus flat-top-pumping of a mid-IR ZGP RISTRA OPO

The influence of the pump intensity profile on the performance of a mid-IR ZGP RISTRA OPO at 6.45???m is studied for a flat-top pump profile and compared to a Gaussian pump distribution at the same pump peak fluence of 0.81?J/cm². Due to a coherent beam transformation a flat-top pump beam with a plane wavefront and excellent beam quality of M ²??1.25 is generated. The output of up to 5?mJ pulse idler energy (0.5?W average idler power) is identical in both cases, showing that flat-top pumping allows a reduction of the OPO crystal volume by 55?% while still maintaining a good output beam quality of M ²<2.7 for the idler and M ²<2.5 for the signal. The experimental results are compared to the SNLO RISTRA model and the limitations of the model are discussed.     

Enhancement of terahertz wave difference frequency generation based on a compact walk-off compensated KTP OPO

A compact, walk-off compensated dual-wavelength KTP OPO near the degenerate point of 2.128 μm pumped by a Nd:YAG pulsed laser is employed as the pump for terahertz (THz) source based on difference frequency generation (DFG) in a GaSe crystal. Coherent THz radiation that is continuously tunable in the range of 81-1617 μm (0.186-3.7 THz) is achieved. An enhancement of 76.7% in average for the THz energies at different wavelengths is realized using the walk-off compensated KTP OPO than the common one. Using a 8 mm-long GaSe crystal, the maximum output THz pulse energy is 48.9 nJ with the peak power of 11 W, corresponding to the energy conversion efficiency of 5.4 × 10^− 6 and the photon conversion efficiency of about 0.09%.     

Effect of resonator length on ZnGeP<Subscript>2</Subscript> doubly resonant optical parametric oscillator pumped by a Tm,Ho:GdVO<Subscript>4</Subscript> laser

The effect of resonator length on ZnGeP₂ doubly resonant optical parametric oscillator was reported in this letter. With the employment of a Tm,Ho:GdVO₄ laser as the pump source at 2.05 μm, we have found that there are obvious peaks of the output power when the resonator lengths are matched to the length of the pump source. The ZGP OPO can generate a maximum output power of 4.27 W at 3.80 μm signal and 4.45 μm idler when the resonator length matches that of the pump source.     

1.57μm被动调Q光学参量振荡器

在半导体泵浦被动调QNd∶GdVO4/Cr4+∶YAG激光腔内,利用KTP晶体实现了高重复频率的内腔OPO的稳定运转。OPO其信号光转换效率为7%,斜效率为10.3%。当泵浦功率7.3W时,可获得平均功率为0.48W,重频15kHz,脉宽6ns,峰值功率达13KW的1570nm激光输出。