Self-phase-locked degenerate femtosecond optical parametric oscillator

We demonstrated a stable degenerate synchronously pumped femtosecond optical parametric oscillator (SPOPO) as a divide-by-2 subharmonic generator. The SPOPO exhibited passive all-optical self-phase-locking between the pump and signal/idler and thus required no external electronic feedback to produce the phase-locked subharmonic. We employed a type I phase-matched, 1-mm-long, periodically poled MgO:LiNbO3 crystal as the nonlinear gain element and an 80 MHz mode-locked Ti:sapphire laser with 180 fs pulses tuned at 775 nm as the pump. The SPOPO generated transform-limited 70 fs phase-locked output pulses centered at 1550 nm. The self-phase-locking operation was confirmed by separate beat-note measurement techniques with respect to the pump laser and with respect to an external cw laser.     

Harmonic repetition-rate femtosecond optical parametric oscillator

We report on a femtosecond optical parametric oscillator (OPO) with a repetition rate of 1 GHz, which is 12 times that of the pump laser used. We also introduce a novel method for operating an OPO with a high harmonic repetition rate which is not determined by the cavity length of the OPO, but rather the cavity length difference between the OPO and its pump laser. Operation of an OPO at 4-times the harmonic repetition rate has been carried out to show the feasibility of this method. The new approach paves the way for constructing a femtosecond OPO working at repetition rates of 10 GHz, or higher, when the pump laser used has a relatively low repetition rate. Received: 26 October 2001 / Revised version: 11 Januar 2002 / Published online: 14 March 2002     

Near-infrared cavity-dumped femtosecond optical parametric oscillator

We demonstrate a high-energy near-infrared cavity-dumped femtosecond optical parametric oscillator (OPO) based on periodically poled lithium niobate. The laser generates 90 nJ pulses at a repetition rate of up to 1 MHz when synchronously pumped by 800 mW output from a femtosecond Ti:sapphire laser. The laser is broadly tunable from 1.0 to 1.5 microm in the signal branch, with a pulse duration of < 60 fs at 1.2 microm. High intracavity power is achieved by running the laser in the regime of positive group-velocity dispersion.     

Synchronized retroreflection-pumped femtosecond optical parametric oscillator

We report a flexible technique for threshold reduction and output power enhancement in synchronously pumped optical parametric oscillators (SPOPOs) based on synchronized retroreflection of the undepleted pump using a collimating system and a delay line, which allows easy and independent adjustment of the spatial and temporal overlap of the retroreflected beam in the nonlinear crystal. The method permits initial synchronization of the forward and retroreflected pump by interferometry, providing threshold reduction before oscillation is initiated. We demonstrate the technique in a femtosecond SPOPO based on BiB3O6, where a threshold reduction of 22% and an output power enhancement of 70% are achieved compared with single-pass pumping, with no detrimental effect on the spectral and temporal characteristics of the output pulses.     

Widely tunable femtosecond fiber optical parametric oscillator

The phase-matching condition in a fiber is discussed. A balance among the different orders of fiber dispersion can be found to achieve a widely tuning modulation instability gain for pumping around the normal dispersion regime. Three coupled nonlinear wave equations are used to simulate the femtosecond fiber optical parametric oscillator. The numerical results show that, through appropriate choice of dispersion, femtosecond pulses with a 180-nm tunable range can be generated when pump wavelength near a fiber’s zero-dispersion wavelength is tuned only 7 nm. Further tuning is limited by the walk-off between the pump and the signal pulses.     

Efficient intracavity generation of visible pulses in a femtosecond near-infrared optical parametric oscillator

We have achieved efficient simultaneous intracavity doubling of the signal frequency and sum-frequency generation between the signal and the pump in a periodically poled LiNbO(3) femtosecond optical parametric oscillator pumped by a Ti:sapphire laser. The responsible mechanisms are second-, third-, and fourth-order quasi-phase matching (QPM). An ~56% poling duty cycle permits efficient even-order QPM. Femtosecond pulses tunable in the visible were generated with a total efficiency of more than 8% for only 480-mW pump power at 80 MHz. Optimization of the poling duty cycle can improve the efficiency further.     

BiB3O6 femtosecond optical parametric oscillator

We report a femtosecond optical parametric oscillator (OPO) based on the nonlinear material BiB3O6. The OPO is synchronously pumped in the blue by the second harmonic of a Kerr-lens-mode-locked Ti:sapphire laser. It can provide wide and continuous tuning across the entire green-yellow-orange-red spectral range with a single crystal and a single set of mirrors. Using a 500 microm BiB3O6 crystal and collinear type I (e+e->o) phase matching in the optical yz plane, a signal wavelength range of 480-710 nm is demonstrated with angle tuning at room temperature at average output powers of 270 mW. With 220 fs blue pump pulses, near-transform-limited signal pulses of 120 fs duration have been obtained at 76 MHz repetition rate.     

Efficient femtosecond optical parametric oscillator pumped by all solid-state mode-locking Yb:YCOB laser

We experimentally demonstrate a femtosecond optical parametric oscillator(OPO) synchronously pumped by a home-made solid-state mode-locking Yb:YCOB laser, which is capable of laser pulse as short as 102 fs and average power of 620 m W at the central wavelength of 1052 nm. By using a periodically poled lithium niobate with tuning of the grating periods from 28.5 to 31.5 μm as the nonlinear gain crystal, tunable femtosecond pulses from 1444 to 1683 nm are realized by conveniently adjusting the OPO cavity length with 76.8 MHz repetition rate. The maximum average output power is 152 m W at 1568 nm, corresponding to an idler power of 75 m W at 3197 nm as well as 36.6% total extraction efficiency.     

Dual-color operation of a femtosecond optical parametric oscillator exhibiting stable relative carrier-envelope phase-slip frequencies

A femtosecond optical parametric oscillator is demonstrated that can operate in a regime where two signal pulses with well-separated center wavelengths are simultaneously resonant. Measurements show that the oscillator output contains a stable modulation at a frequency corresponding to the difference in the carrier-envelope phase-slip frequencies of the co-resonant pulses. The physical origin of this internal beat signal is attributed to second-order mixing effects, and its frequency is shown to be consistent with theory.     

Synchronously pumped femtosecond optical parametric oscillator at 1053 nm

A femtosecond optical parametric oscillator synchronously pumped by a Ti:Sapphire oscillator is reported. By the cavity length tuning, the signal wavelength is continuously tuned from 1000 to 1200 nm. The average output power of 32 mW is obtained at 1053 nm. The pulse width is measured to be 342 fs by intensity autocorrelation method. In addition, we observed bichromatic emission during the cavity length tuning process. Supported by the National High Technology Program Research and Development Program of China, the National Natural Science Foundation of China (Grant Nos. 60490280 and 10804128), and the National Basic Research Program of China (Grant No. 2007CB815104)     

Megahertz optical parametric amplifier pumped by a femtosecond oscillator

We demonstrate, for the first time to our knowledge, an optical parametric amplifier directly pumped by a femtosecond oscillator. Wavelength-tunable pulses in the ranges 0.65-0.85 microm (signal) and 1.4-2.5 microm (idler) are generated at a repetition frequency of 1 MHz. For pumping the beta-barium borate crystal we use a microjoule Yb:KY(WO4)2 femtosecond oscillator with cavity dumping. Pulses with 30 nJ of energy and a duration of 16 fs are achieved from a supercontinuum seed generated in a sapphire plate.     

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.     

Ti:sapphire second-harmonic-pumped visible range femtosecond optical parametric oscillator

A β-barium borate (BBO) femtosecond optical parametric oscillator (OPO) pumped by the second-harmonic of a modelocked 82 MHz Ti:sapphire laser is described. With intracavity dispersion compensation, pulse durations down to 30 fs are obtained with a total average power up to 100 mW. The current wavelength range, with a 400 nm pump, is from 566 nm to 676 nm. Unusual tuning characteristics, including bichromatic emission, are presented in detail and explained theoretically.     

Compact, efficient 344-MHz repetition-rate femtosecond optical parametric oscillator

We describe configurations of a novel synchronously pumped femtosecond optical parametric oscillator based on the crystal RbTiOAsO(4) and operating with a signal-pulse-repetition frequency as high as 344 MHz. Average signal powers as high as 600 mW and pulse durations of 78 fs are demonstrated at a wavelength of 1.25 microm, and a characterization of the signal output using frequency-resolved optical gating implies asymmetric near-sech(2)(t) intensity-profile pulses with significant amounts of spectral cubic phase.     

高效率LiB3O5光参量振荡器

本文报道LiB_3O_5(LBO)光参量振荡的运转.输出波长范围为:0.956～1.205μm和1.488～1.583μm(0.828～0.801μm).最高输出能量大于70mJ/pulse,效率为43%.文中还给出了双轴晶体LBO的相位匹配曲线和有效非线性系数的计算方法及结果.     

Low-threshold femtosecond optical parametric oscillator based on chirped-pulse frequency conversion

We report what is to our knowledge the first demonstration of a femtosecond optical parametric oscillator based on chirped-pulse frequency conversion in a long crystal of aperiodically poled potassium titanyl phosphate. The minimum pump threshold power was 15 mW, and a signal slope efficiency of 35% was achieved. Continuous tuning from 1190 to 1450 nm was obtained for an average pump power of 800 mW.     

Efficient intracavity optical parametric oscillator with diode side-pumped electro-optic Q-switched laser

An efficient intracavity single-resonant optical parametric oscillator (OPO) at 1.571-μm eye-safe range using a non-criticaily phase-matched KTP crystal is reported. The OPO is excited by a diode side-pumpedelectro-optic Q-switched Nd:YAG laser at 1.064 μm. Signal pulse of 97 mJ and 3.56 ns is obtained under the input electric energy of 2.3 J, corresponding to a slope efficiency of 4.2%, and a repetition rate range of 1--30 Hz.     

Efficient, high-power, ytterbium-fiber-laser-pumped picosecond optical parametric oscillator

We report a high-power picosecond optical parametric oscillator (OPO) synchronously pumped by a Yb fiber laser at 1.064 μm, providing 11.7 W of total average power in the near to mid-IR at 73% extraction efficiency. The OPO, based on a 50 mm MgO:PPLN crystal, is pumped by 20.8 ps pulses at 81.1 MHz and can simultaneously deliver 7.1 W of signal at 1.56 μm and 4.6 W of idler at 3.33 μm for 16 W of pump power. The oscillator has a threshold of 740 mW, with maximum signal power of 7.4 W at 1.47 μm and idler power of 4.9 W at 3.08 μm at slope efficiencies of 51% and 31%, respectively. Wavelength coverage across 1.43-1.63 μm (signal) and 4.16-3.06 μm (idler) is obtained, with a total power of ~11 W and an extraction efficiency of ~68%, with pump depletion of ~78% maintained over most of the tuning range. The signal and idler output have a single-mode spatial profile and a peak-to-peak power stability of ±1.8% and ±2.9% over 1 h at the highest power, respectively. A signal pulse duration of 17.3 ps with a clean single-peak spectrum results in a time-bandwidth product of ~1.72, more than four times below the input pump pulses.     

Carrier-phase control among subharmonic pulses in a femtosecond optical parametric oscillator

We have generated femtosecond subharmonic pulses by using an optical parametric oscillator. The optical frequencies of the idler and the signal are one third and two thirds, respectively, of the optical frequency of the pump pulse. The carrier phase of the signal pulse relative to that of the pump pulse was locked by electronic feedback. The carrier-envelope phase slip frequency of the signal pulse relative to that of the pump was locked to F/6 , where F is defined as the repetition frequency.     

Entangled-cavity optical parametric oscillator for mid-infrared pulsed single-longitudinal-mode operation

We report a pulsed doubly resonant optical parametric oscillator that uses an original entangled-cavity geometry. This compact source (total volume of 1 L, including the pump laser) displays single-frequency operation (linewidth, <100 MHz), a high repetition rate (>10 kHz), low threshold (<10 muJ), and wide tuning in the mid-infrared. These properties qualify pulsed doubly resonant optical parametric oscillators as powerful tools for applications in such fields as nonlinear spectroscopy, lidar, and pollutant detection.