2.5-GHz repetition-rate singly resonant optical parametric oscillator synchronously pumped by a mode-locked diode oscillator amplifier system

We report on an optical parametric oscillator (OPO) that is synchronously pumped directly by a diode laser. This laser is an actively mode-locked master-oscillator power-amplifier system that produces 20-ps pulses at 927 nm with a repetition rate of 2.5 GHz and an average power of 0.9 W. The OPO, which is a singly resonant device based on periodically poled lithium niobate, generates 7.8-ps pulses. The OPO threshold is 300 mW of average pump power, and the maximum average idler output power is 78 mW at a wavelength of 2100 nm. By changing the crystal temperature we can wavelength tune the output in the ranges 1530-1737 nm (signal) and 1986-2348 nm (idler). Rapid wavelength tuning of the OPO over 46 nm (signal) and 74 nm (idler) is achieved through tuning the cavity length over 28 microm by use of a piezoelectric transducer.     

Rapid infrared wavelength access with a picosecond PPLN OPO synchronously pumped by a mode-locked diode laser

We theoretically and experimentally investigate wavelength tuning of synchronously pumped optical parametric oscillators (OPOs) on changing the cavity length or the pump-repetition rate. Conditions for rapid and wide-range wavelength access are derived. Using an OPO pumped directly by a mode-locked diode-laser master-oscillator power-amplifier (MOPA) system, an all-electronically controlled access to near- and mid-infrared wavelengths is demonstrated. The singly (signal) resonant OPO is based on periodically poled lithium niobate (PPLN) and emits 8 ps idler pulses at a repetition rate of 2.5 GHz in the wavelength range 1986 to 2348 nm (signal: 1530 to 1737 nm). Wavelength tuning over 114 nm (signal) and 189 nm (idler) is achieved solely by electronically varying the repetition rate of the diode-laser oscillator over 720 kHz. By controlling the repetition rate with a programmable driver, an arbitrary emission sequence of the OPO on two wavelength channels is generated, with access times as short as 10 μs. 11 OPO wavelengths equally spaced in the range 1627–1689 nm (signal) or 2054–2154 nm (idler) could be addressed. Received: 6 September 2000 / Revised version: 16 March 2001 / Published online: 23 May 2001     

Continuous-wave singly resonant optical parametric oscillator based on periodically poled RbTiOAsO(4)

We report a continuous-wave optical parametric oscillator (OPO) based on periodically poled RbTiOAsO(4) (PPRTA). The singly resonant OPO, which is located within a Ti:sapphire laser, has a high-finesse signal cavity and delivers a maximum output power of 270 mW to the nonresonant idler wave at 2.92mum , through a 4.5-mm PPRTA crystal. For room-temperature operation and a crystal with a 30-mu;m grating period, pump tuning over 838-848 nm results in OPO tuning over 1.13-1.27mum (signal) and 2.53-3.26mum (idler), limited by the bandwidth of optical coatings. PPRTA exhibits thermal properties superior to those of periodically poled LiNbO(3) .     

1.59 W, single-frequency, continuous-wave optical parametric oscillator based on MgO:sPPLT

A watt-level, single-frequency, continuous-wave (cw) singly resonant optical parametric oscillator (OPO) based on MgO:sPPLT is described. Pumped in the green by a frequency-doubled cw diode-pumped Nd:YVO(4) laser at 532 nm, the OPO can provide up to 1.59 W of single-frequency idler output with a linewidth of ~7 MHz at pump depletions of as much as 67%. Using a compact ring resonator and optimized focusing in a 30 mm crystal, a singly resonant oscillation threshold of 2.84 W has been obtained under single-pass pumping. With a single grating period of 7.97 microm, continuous signal and idler coverage over 852-1417 nm is obtained by temperature tuning between 61 degrees C and 236 degrees C. The influence of thermal lensing on idler output power across the SRO tuning range is also verified.     

Intracavity-pumped Cr2+:ZnSe laser with ultrabroad tuning range between 1880 and 3100 nm

We obtained, what is to our knowledge, record tuning from an intracavity-pumped gain-switched Cr2+:ZnSe laser. In the experiments, a polycrystalline Cr2+:ZnSe sample with an absorption of about 43% at 1570 nm was used to minimize reabsorption losses at the lasing wavelengths below 2000 nm. By placing the gain medium inside the cavity of a pulsed KTP optical parametric oscillator (OPO) operating at 1570 nm, smooth, continuous tuning was achieved in the 1880-3100 nm range with four different sets of cavity optics. As high as 145 mW of average laser output power was obtained at 2365 nm with 1.2 W of intracavity OPO power.     

Spectral properties and numerical modelling of a critically phase-matched nanosecond LiB3O5 Optical Parametric Oscillator

We report on the spectral properties and numerical modelling of a singly resonant Optical Parametric Oscillator (OPO) of Lithium-triBOrate (LBO). The OPO is pumped by the second, third or fourth harmonic of an injection-seeded,Q-switched Nd:YAG laser. The measured OPO parameters are the tuning range, the threshold, the spectral linewidth, the efficiency and the output power. For the LBO-OPO critical type-I phase-matching (xy-plane) provides a wide tuning range and optimum values of the effective nonlinear coefficient. Pumped, for example, by the 355nm third harmonic the spectral range extends from 414 nm to 2.47 µm. With a 15 mm long crystal the OPO generates a total output-pulse energy of 77 mJ with an efficiency of 45%. For 266 nm pump radiation the signal wave is in the near ultraviolet at 307–325 nm. If pumped at 532 nm the OPO generates simultaneously two pairs of signal and idler waves in the infrared (0.707–2.15 µm). The pulse-energy fluctuations of the two pairs are correlated. If, however, the OPO is injection-seeded at one of the signal waves the two wavelength pairs are anti-correlated. The observed wavelength tuning as well as the measured spectral line-widths, threshold energies and efficiencies are in agreement with the values predicted by computer simulation.     

Atomic and molecular spectroscopy with a continuous-wave, doubly resonant, monolithic optical parametric oscillator

Doppler-broadened atomic and molecular spectra were observed with a one octave tunable, continuous-wave, doubly resonant, monolithic optical parametric oscillator (OPO) using 5% MgO-doped LiNbO₃ as a non-linear crystal with a birefringent phase-matching configuration. By tuning the frequency of a pump laser, longitudinal mode selection over 20 successive modes, corresponding to a 60 GHz span, was possible, owing to the simple structure of the monolithic OPO. Continuous frequency tuning was achieved using an external waveguide-type electrooptic phase modulator (EOM). By changing the modulation frequency of the EOM, frequency tuning of the optical sidebands over 12 GHz was possible, which is larger than the one free spectral range of the monolithic cavity of 3 GHz. We could observe the Cs-D₁ (894 nm), Cs-D₂ (852 nm), Rb-D₁ (795 nm), acetylene R9 (1520 nm) and P9 (1530 nm) transitions with the single monolithic OPO.     

Rapidly tunable continuous-wave optical parametric oscillator pumped by a fiber laser

We report on rapid, all-electronically controlled wavelength tuning of a continuous-wave (cw) optical parametric oscillator (OPO) pumped by an ytterbium fiber laser. The OPO is singly resonant for the signal wave and consists of a 40-mm-long periodically poled lithium niobate crystal in a four-mirror ring cavity. By tuning of the fiber-laser wavelength over 33 nm through an intracavity acousto-optic tunable filter, the OPO idler wavelength is tuned from 3160 to 3500 nm in 330 micros, corresponding to an idler frequency-tuning speed of 28 THz/ms. At a fiber-laser power of 6.6 W at 1074 nm, the singly resonant OPO generates 1.13-W cw idler radiation at 3200 nm.     

Fiber-laser-pumped continuous-wave singly resonant optical parametric oscillator

We report on what is to our knowledge the first continuous-wave (cw) optical parametric oscillator (OPO) that is pumped by a tunable fiber laser. The OPO is singly resonant for the signal wave and consists of a 40-mm-long periodically poled LiNbO(3) crystal in a four-mirror ring cavity. At a pump power of 8.3 W provided by the wavelength-tunable Yb-doped fiber laser, the singly resonant OPO generates 1.9 W of 3200-nm cw idler radiation. The singly resonant OPO was tuned from 1515 to 1633 nm (signal) and from 3057 to 3574 nm (idler) by means of the crystal temperature and poling period. We obtained a wide idler tuning range, from 2980 to 3700 mn, by tuning the wavelength of the fiber laser from 1032 to 1095 nm.     

Microsecond pulsed optical parametric oscillator pumped by a Q-switched fiber laser

We report on what is to our knowledge the first optical parametric oscillator (OPO) pumped by microsecond pulses from a wavelength-tunable solid-state laser. The singly resonant OPO (SRO) is based on a periodically poled LiNbO3 crystal and pumped with 2.1-micros-long pulses from an actively Q-switched Yb fiber laser. At an average fiber laser power of 3.6 W, the SRO generates 1.9-micros-long pulses with a repetition rate of 25 kHz and an average power of 560 mW at 3360 nm. The SRO was tuned from 1518 to 1634 nm (signal) and from 3145 to 3689 nm (idler) via the crystal temperature and poling period. By all-electronic tuning of the fiber laser wavelength over 19 nm, tuning of the mid-infrared idler wavelength over 195 nm was achieved.     

Optical parametric oscillation in periodically poled lithium niobate driven by a diode-pumped Q-switched erbium fiber laser

We describe what is to our knowledge the first nanosecond periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) driven by a fiber laser. The source was frequency doubled by a PPLN sample before pumping a second, 20-mm-long, PPLN crystal. The OPO threshold was <10muJ, with pump depletions of as much as 45% and a tunable signal range of 945-1450 nm (1690-4450-nm idler range). We demonstrated 130-nm signal tuning by varying the pump wavelength and doubling crystal's temperature. Also, we achieved 15-nm tuning with all crystals at a constant temperature. The results demonstrate the potential of the fiber laser:PPLN combination for practical, versatile, and tunable sources.     

Frequency-agile kilohertz repetition-rate optical parametric oscillator based on periodically poled lithium niobate

We report kilohertz repetition-rate pulse-to-pulse wavelength tuning from 3.22 to 3.7 mum in a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO). Rapid tuning over 400 cm(-1) with random wavelength accessibility is achieved by rotation of the pump beam angle by no more than 24 mrad in the PPLN crystal by use of an acousto-optic beam deflector. Over the entire tuning range, a near-transform-limited OPO bandwidth can be obtained by means of injection seeding with a single-frequency 1.5-mum laser diode. The frequency agility, high repetition rate, and narrow bandwidth of this mid-IR PPLN OPO make it well suited as a lidar transmitter source.     

Continuous-wave optical parametric oscillator based on periodically poled KTiOPO(4) and its application to spectroscopy

We report a continuous-wave, doubly resonant optical parametric oscillator (OPO) based on the nonlinear material periodically poled KTiOPO(4) and its application to spectroscopy. The OPO, which is pumped by a diode-pumped frequency-doubled Nd:YLF laser at 523 nm, has a low pump-power threshold of 25 mW and can deliver 10 mW of single-frequency output at 1.65 mum for a pump power of 200 mW. The idler wavelength can be temperature tuned at a rate of 0.73 nm/( degrees )C , and smooth tuning of the output frequency over ~3 GHz is achieved by smooth tuning of the pump laser. We demonstrate the practicality of the OPO by recording the absorption spectrum of methane near 1649 nm.     

临界及非临界相位匹配KTP光学参量振荡器

报道了利用Nd:YAG激光器二次谐波532nm及基频波1064nm作抽运源,采用临界及非临界相位匹配方式抽运KTP光学参量振荡器的实验结果.实验中获得了具有实用价值的1.53-1.84um人眼安全激光,KTP光学参量振荡器输出总量最大达130mJ,最高能量转换效率64%.分析比较了调谐范围、离分角、接收角、阈值及转换效率,讨论离分角对参量输出的光束质量、转换效率的影响.     

Compact, 1.5 mJ, 450 MHz, CdSiP2 picosecond optical parametric oscillator near 6.3 μm

We report a compact, efficient, high-energy, and high-repetition-rate mid-IR picosecond optical parametric oscillator (OPO) based on the new nonlinear material CdSiP(2) (CSP). The OPO is synchronously pumped by a master oscillator power amplifier system at 1064.1 nm, providing 1 μs long macropulses constituting 8.6 ps micropulses at 450 MHz, and it can be tuned over 486 nm across 6091-6577 nm, covering the technologically important wavelength range for surgical applications. Using a compact (～30 cm) cavity and improved, high-quality nonlinear crystal, idler macropulse energy as high as 1.5 mJ has been obtained at 6275 nm at a photon conversion efficiency of 29.5%, with >1.2 mJ over more than 68% of the tuning range, for an input macropulse energy of 30 mJ. Both the signal and idler beams are recorded to have good beam quality with a Gaussian spatial profile, and the extracted signal pulses are measured to have durations of 10.6 ps. Further, from the experimentally measured transmission data at 1064 nm, we have estimated the two-photon absorption coefficient of CSP to be β=2.4 cm/GW, with a corresponding energy bandgap, E(g)=2.08 eV.     

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.     

Quasi-phase-matched generation of tunable blue light in a quasi-periodic structure

We present what is to our knowledge a new approach to generating tunable blue light by cascaded nonlinear frequency conversion in a single LiTaO3 crystal. Simultaneous quasi-phase matching of an optical parametric generation process and a sum-frequency mixing process is achieved by means of structuring the crystal with a quasi-periodic optical superlattice. The spectral (wavelength tuning and bandwidth) and power characteristics of the blue-light generation are studied with a fixed-wavelength 532-nm picosecond laser and a wavelength-tunable nanosecond optical parametric oscillator (OPO) as the pump sources. By tuning the OPO wavelength, we could tune the blue output over approximately 20 nm. Temperature tuning of the blue output at a fixed pump wavelength of 532 nm was limited to approximately 1.5 nm. A maximum blue power of 15 microW was generated at a pump power of 0.5 mW, corresponding to an efficiency of 3%.     

Narrowband tuning of an injection-seeded pulsed optical parametric oscillator based on a self-adaptive, phase-conjugate cavity mirror

Narrowband tuning of a pulsed optical parametric oscillator (OPO) is achieved with a self-adaptive injection-seeded optical cavity employing a phase-conjugate reflector. This approach is used in a novel OPO system based on periodically poled KTiOPO4 and pumped at 532 nm by a pulsed Nd:YAG laser. The OPO is injection seeded at 835-855 nm by a continuous-wave tunable diode laser, which also enables a Rh:BaTiO3 photorefractive crystal to act as a wavelength-selective phase-conjugate reflector, with no need for active control of cavity length. The single-longitudinal-mode tunability and operational simplicity of this OPO system are demonstrated experimentally.     

Wide wavelength tuning of an optical parametric oscillator through electro-optic shaping of the gain spectrum

We present a novel technique for tuning an optical parametric oscillator (OPO) through electro-optically induced shape variations of the parametric gain spectrum in quasi-phase-matched lithium niobate (LN). The diode-pumped, triply resonant continuous-wave OPO is based on a 58-mm-long LN crystal that consists of three equally long sections, the outer sections being periodically poled with a 50% duty cycle. The center section is single-domain material and serves as a tunable phase shifter through the electro-optic effect. By application of a voltage of up to 1230 V, the OPO signal and idler wavelengths are tuned over 102 nm from 1560 to 1660 nm, in good agreement with theory.     

Narrowband bulk Bragg grating optical parametric oscillator

A narrowband, pulsed optical parametric oscillator (OPO) whose output coupler is a bulk glass Bragg grating is demonstrated. The OPO is based on periodically poled KTiOPO4 and is pumped by a pulsed, frequency-doubled Nd:YAG laser at 532 nm, generating a signal at 975 nm with a total efficiency of 35%. This novel and compact device shows a spectral bandwidth of 0.16 nm (50 GHz), a decrease by a factor of 20 compared with that when a conventional mirror is used. By using a folded cavity, we demonstrate tunable radiation with a tuning range of 60 nm and maintained spectral bandwidth.