Low-pump-threshold continuous-wave singly resonant optical parametric oscillator

We describe a compact all-solid-state continuous-wave singly resonant optical parametric oscillator (SRO) with a minimal pump-power requirement. The SRO is based on periodically poled LiNbO(3) as the nonlinear material and is pumped by a 1-W diode-pumped Nd:YVO(4) minilaser at 1.064 microm . By exploiting the intracavity pumping technique in a 50-mm crystal, we have achieved SRO operation threshold at a diode pump power of only 310 mW.At 1 W of input diode power, the SRO delivers 70 mW of output power in the nonresonant idler at 3.66 microm , at a photon conversion efficiency of 55%. Multiparameter tuning of the SRO yields a signal wavelength range from 1.45 to 1.60 microm and an idler wavelength range from 3.16 to 4.02 microm in the mid infrared. The device is characterized by robust turnkey operation and long-term amplitude-stable performance.     

中红外连续波单谐振光学参量振荡器热致相位失配

为了研究热致相位失配对中红外连续波单谐振光学参量振荡器(CW-SRO)输出效率的影响, 结合CW-SRO计算模型和热传导方程,利用有限元分析方法,重点对输出3.3 m波长闲频光的CW-SRO进行了分析。计算了不同信号光输出耦合率及不同泵浦功率下CW-SRO晶体输出截面上热致相位失配量的分布。由计算结果可以看出:晶体吸收腔中振荡信号光是导致晶体热效应的主要因素;在相同的输入条件下,泵浦功率在30 W以上时CW-SRO的热致相位失配将会大大降低其泵浦损耗率;通过增加信号光输出耦合率的方法,可以减少热致相位失配对CW-SRO输出效率的影响,但CW-SRO的振荡阈值会增加。     

中红外连续波单谐振光学参量振荡器热致相位失配

为了研究热致相位失配对中红外连续波单谐振光学参量振荡器(CW-SRO)输出效率的影响, 结合CW-SRO计算模型和热传导方程,利用有限元分析方法,重点对输出3.3 m波长闲频光的CW-SRO进行了分析。计算了不同信号光输出耦合率及不同泵浦功率下CW-SRO晶体输出截面上热致相位失配量的分布。由计算结果可以看出：晶体吸收腔中振荡信号光是导致晶体热效应的主要因素;在相同的输入条件下,泵浦功率在30 W以上时CW-SRO的热致相位失配将会大大降低其泵浦损耗率;通过增加信号光输出耦合率的方法,可以减少热致相位失配对CW-SRO输出效率的影响,但CW-SRO的振荡阈值会增加。     

Efficient continuous-wave eye-safe region signal output from intra-cavity singly resonant optical parametric oscillator

We report an efficient continuous-wave (CW) tunable intra-cavity singly resonant optical parametric oscillator based on the multi-period periodically poled lithium niobate and using a laser diode (LD) end-pumped CW 1064 nm Nd:YVO₄ laser as the pump source. A highly efficiency CW operation is realized through a careful cavity design for mode matching and thermal stability. The signal tuning range is 1401-1500 nm obtained by varying the domain period. The maximum output power of 2.2 W at 1500 nm is obtained with a 17.1 W 808 nm LD power and the corresponding conversion efficiency is 12.9%.     

Efficient continuous-wave eye-safe region signal output from intra-cavity singly resonant optical parametric oscillator

We report an efficient continuous-wave (CW) tunable intra-cavity singly resonant optical parametric oscillator based on the multi-period periodically poled lithium niobate and using a laser diode (LD) end-pumped CW 1064 nm Nd:YVO 4 laser as the pump source.A highly efficiency CW operation is realized through a careful cavity design for mode matching and thermal stability.The signal tuning range is 1401-1500 nm obtained by varying the domain period.The maximum output power of 2.2 W at 1500 nm is obtained with a 17.1 W 808 nm LD power and the corresponding conversion efficiency is 12.9%.     

Cascaded continuous-wave singly resonant optical parametric oscillator pumped by a single-frequency fiber laser

We present a cascaded continuous-wave singly resonant optical parametric oscillator (SRO) delivering idler output in mid-IR and terahertz frequency range. The SRO was pumped by an ytterbium-doped fiber laser with 27 W linear polarization pump powers, and based on periodically poled MgO:LiNbO₃ crystal (PPMgLN) in two-mirror linear cavity. The PPMgLN is 50 mm long with 29.5 μm period. The idler power output at 3811 nm was obtained 2.6 W. The additional spectral components that have been attributed to cascaded optical parametric processes are described at increasing pump levels. Besides the initial signal component at about 1476.8 nm, further generated wavelengths with frequency shifts about 47 cm^?1, 94 cm^?1 and 104 cm^?1 were observed. It was speculated that the idler waves lie in the terahertz (THz) domain from the observed results.     

Self-guided operation of singly resonant continuous-wave optical parametric oscillator based on bulk MgO-doped PPLN

We report on a self-guided operation of a green-pumped singly resonant continuous-wave optical parametric oscillator with a bulk MgO-doped PPLN crystal. It is achieved by increasing the OPO cavity length beyond the stability boundary so that the OPO can only oscillate with formation of a thermally induced waveguide inside the crystal. The effects of the thermal waveguide on the OPO performance are studied by measuring output power characteristics at different cavity lengths. Improvement of spatial mode quality and stability of output power by self-guiding is demonstrated. Measurement of temporal characteristics proves that formation of the waveguide originates from the photo-thermal effect in the nonlinear crystal by absorption of pump power.     

Thermal effects in singly resonant continuous-wave optical parametric oscillators

Stability and tuning characteristics of continuous-wave optical parametric oscillators (CW OPOs) are affected by various thermal effects arising from optical absorption in nonlinear crystals. In this paper, we present an experimental study of such effects in a singly resonant CW OPO. The OPO operates in the 3-μm mid-infrared region and it is based on a MgO-doped periodically poled lithium niobate crystal. We focus our study on two thermally induced phenomena that have been recently reported to exist in singly resonant CW OPOs: optical bi-stability and thermal self-locking. Thermal self-locking effect, which is known to alter the stability and tuning properties of doubly and triply resonant CW OPOs, is shown to be also of importance in singly resonant OPOs. We report the stability and tuning characteristics of a thermally loaded OPO and discuss a simple temperature-tuning method that can be used to scan the OPO idler frequency continuously over several THz.     

High-power, continuous-wave, singly resonant optical parametric oscillator based on MgO:sPPLT

We report a high-power, widely tunable, cw singly resonant optical parametric oscillator (OPO) based on MgO:sPPLT. The OPO is pumped in the green by a cw diode-pumped Nd:YVO(4) laser at 532 nm and can provide continuously tunable output across 848-1430 nm. Using a 30 mm crystal and double-pass pumping, an oscillation threshold of 2.88 W has been obtained, and single-pass idler powers in excess of 1.51 W have been generated over 1104-1430 nm for 6W of pump power at an extraction efficiency of 25.2% and photon conversion efficiency of 56.7%.     

Microchip laser-pumped continuous-wave doubly resonant optical parametric oscillator

We report what we believe to be the first use of a multilongitudinal-mode frequency-doubled microchip laser to pump a doubly resonant optical parametric oscillator (OPO). This compact OPO is based on potassium titanyl phosphate (KTP) and operates with a low pump power threshold of 35 mW. The OPO output consists of a single pair of signal and idler modes even though it is pumped with a multilongitudinal-mode pump laser. We achieved smooth tuning (1.7 GHz) of the output frequencies by temperature tuning of the pump laser.     

Observation of thermal-induced optical guiding and bistability in a mid-IR continuous-wave, singly resonant optical parametric oscillator

We report the observation of thermal-induced optical guiding and bistability in a mid-IR cw, singly resonant optical parametric oscillator (SRO) at approximately 3.2 microm. The SRO employs a MgO:PPLN crystal as the gain medium and a 1-nm-linewidth Yb-fiber laser at 1.064 microm as the pump source. As soon as the pump power reaches the thermal guiding threshold at 16.5 W, the SRO shows a step increase in the parametric efficiency by a factor of 2.5. At 25 W pump power, the SRO generated 5.3 and 1.2 W at 1.58 and 3.23 microm, respectively, with single-longitudinal-mode performance for the 3.23 microm radiation.     

Diode-pumped singly resonant continuous-wave optical parametric oscillator with wide continuous tuning of the near-infrared idler wave

We demonstrate wide, continuous tuning of the single-frequency idler wave of a cw singly resonant optical parametric oscillator (SRO). The SRO consists of a periodically poled LiNbO(3) crystal for quasi-phase matching in a four-mirror signal-resonant ring cavity. The SRO, excited by 2.25 W of 924-nm radiation from an InGaAs diode laser, generates as much as 200 mW of single-frequency 2.1-mum idler radiation. We tune the idler frequency continuously within a range as large as 56 GHz by changing the wavelength of the diode pump laser. The versatility of this continuously tunable single-frequency infrared source is demonstrated by recording of N(2)O rovibrational absorption lines near 2.1 mum.     

Combined wide pump tuning and high power of a continuous-wave, singly resonant optical parametric oscillator

A new singly resonant, single-frequency optical parametric oscillator (OPO) has been developed for the 2.6–4.7 m infrared wavelength region, using a high power (>20 W), widely tunable (1024–1034 nm) Yb:YAG pump source. With the OPO frequency stabilized with an intracavity etalon, the OPO achieved an idler output power of 3 W at 2.954 m. Tuning of the idler frequency was achieved by longitudinal mode-hop tuning of the pump source (FSR 100 MHz). In this way an idler frequency scan of 100–150 GHz could be obtained, after which the signal frequency hops ahead over the FSR of the intracavity etalon of the OPO (207 GHz). Due to un-optimized mirror coatings for the OPO cavity and PPLN crystal, the frequency stability was limited to 90 MHz over 1 s, with an unaffected long-term frequency stability of 250 MHz over 200 seconds. PACS 42.65.Yj; 82.80.Kq; 42.62.Fi     

Active mode locking of continuous-wave doubly and singly resonant optical parametric oscillators

We report on what we believe to be the first active mode locking of near-degenerate, doubly and singly resonant cw-pumped optical parametric oscillators (OPOs). We show experimentally that a steady-state regime of short pulses is reached in a few tens of microseconds under cw pumping. The oscillation buildup dynamics of both OPOs is also explored, evidencing an unusual transient behavior in the mode-locking process.     

Diffractive effects in singly resonant continuous-wave parametric oscillators

I /k_P=0.33and0.50. It is found that the ratio of pump depletion to maximal depletion as a function of the ratio of pump power to threshold power agrees with the plane-wave prediction to within 5%, for a wide range of focusing conditions. The observed trends are explained as resulting from intensity- and phase-dependent mechanisms. Received: 19 January 1998/Revised version: 13 March 1998     

Singly resonant continuous-wave optical parametric oscillator pumped by a diode laser

We report on what is believed to be the first singly resonant cw optical parametric oscillator (SRO) that is directly pumped by a diode laser. The SRO consists of a 38-mm-long periodically poled LiNbO(3) crystal in a four-mirror signal-resonant ring cavity. Pumped by 2.5 W of 925-nm diode-laser radiation, the SRO generates 480 mW of single-frequency idler radiation at 2.1mum . The wavelengths of the signal and the idler output are tuned in the ranges of 1.55 to 1.70mum and 2.03 to 2.29mum, respectively, by tuning the wavelength of the diode laser from 924.0 to 925.4 nm.     

Doubly resonant continuous-wave optical parametric oscillator pumped by a single-mode diode laser

The performance characteristics of a doubly (signal and idler) resonant continuous-wave optical parametric oscillator based on periodically poled lithium niobate and pumped by a 100-mW single-mode laser diode at 810 nm are reported. Pump power thresholds as low as 16 mW and wavelength tuning over the range 1.15-1.25 microm at the signal and 2.31-2.66 microm at the idler were achieved through variation of crystal temperature, pump wavelength, and grating period. Up to 5 mW of signal output was obtained with the single-mode diode pump, and signal powers of up to 39 mW were obtained when pumping with a 400-mW injection-locked broad-area diode laser.     

Theory of intracavity absorption spectroscopy with a singly resonant optical parametric oscillator

The suitability of a singly resonant optical parametric oscillator pumped by a one-mode field and oscillating simultaneously in several signal and idler modes, for intracavity absorption spectroscopic measurements is studied theoretically. For steadystate operation, the enhancement factor ξ indicating the increased detection sensitivity, is shown to be mainly determined by the ratio of the intensity in one of the signal modes to the intensity (per mode) due to parametric fluorescence. Hence, rather high values of ξ, say of order 10⁸ or more, might be attainable, at least in principle. For pulsed operation, on the other hand, a numerical analysis leads to the result that for realistic pulse durations only moderate values of ξ (smaller than some 10³) will be found. Paper given in parts at the 6th Vavilov-Conference on Nonlinear Optics, Novosibirsk, USSR, 1979.     

Continuous-wave, singly resonant, intracavity parametric oscillator

Performance characteristics of a continuous-wave intracavity optical parametric oscillator are described by use of an experimental arrangement comprising a KTP singly resonant oscillator located within a Ti:sapphire laser cavity and analyzed by use of a steady-state model. Internal and external powers, circulating fields, tuning ranges, spectral bandwidths, and amplitude-stability levels are measured and discussed. The nonresonant idler tunes from 2.53 to 2.87 microm, delivers a maximum output power of approximately 0.4W and displays long-term amplitude-stable operation. The total downconverted power approaches the optimum power coupled out of the Ti:sapphire laser in the absence of frequency conversion.