Dual‐wavelength optical parametric oscillator using antiresonant ring interferometer

A novel technique for coupling of two resonant optical cavities using an antiresonant ring (ARR) interferometer is reported. By deploying two synchronously‐pumped femtosecond optical parametric oscillators (OPOs), it is shown that the use of an ARR can provide an intracavity common path for the two oscillating fields, but without gain coupling between the two nonlinear media. The new technique permits the generation of two signal (idler) wavelengths, which can be independently and arbitrarily varied across the OPO tuning range. The absence of gain coupling also enables unrestricted and uninterrupted tuning through wavelength degeneracy at any arbitrary point within the OPO tuning range. It is shown that signal wavelength pairs tunable across 1500–1580 nm, corresponding to a frequency separation from ∼ 10 THz down to exact degeneracy, can be generated from the coupled OPOs, limited only by the reflectivity of the available mirrors.     

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.     

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.     

Dual-wavelength, two-crystal, continuous-wave optical parametric oscillator

We report a cw optical parametric oscillator (OPO) in a novel architecture comprising two nonlinear crystals in a single cavity, providing two independently tunable pairs of signal and idler wavelengths. Based on a singly resonant oscillator design, the device permits access to arbitrary signal and idler wavelength combinations within the parametric gain bandwidth and reflectivity of the OPO cavity mirrors. Using two identical 30 mm long MgO:sPPLT crystals in a compact four-mirror ring resonator pumped at 532 nm, we generate two pairs of signal and idler wavelengths with arbitrary tuning across 850-1430 nm, and demonstrate a frequency separation in the resonant signal waves down to 0.55 THz. Moreover, near wavelength-matched condition, coherent energy coupling between the resonant signal waves, results in reduced operation threshold and increased output power. A total output power >2.8 W with peak-to-peak power stability of 16% over 2 h is obtained.     

Dye laser pumped, continuous-wave KTP optical parametric oscillators

4 (KTP) optical parametric oscillators (OPOs) with pump and idler resonant cavities. With a linear two-mirror cavity the pump power at threshold was 70 mW. The single-frequency signal and idler output wavelengths were tuned in the range of 1025 to 1040 nm and 1250 to 1380 nm by tuning the dye laser in the range of 565 to 588 nm. With a dual three-mirror cavity the threshold was 135 mW. Pumped by 500 mW of 578 nm radiation the 1040 nm single-frequency signal wave output power was 84 mW. Power and frequency stable operation with a spectral bandwidth of less than 9 MHz was obtained by piezo-electrically locking the length of the pump resonant cavity to the dye laser wavelength. Similar performance was achieved by placing the idler resonant OPO inside the resonator of the dye laser. With this system power stable and single-frequency operation was achieved with a spectral bandwidth of less than 11 MHz for the idler wave. Received: 3 February 1998/Revised version: 9 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.     

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.     

Optimally-output-coupled, 17.5 W,fiber-laser-pumped continuous-wave optical parametric oscillator

We present a stable, high-power, fiber-laser-pumped, continuous-wave (cw), singly resonant optical parametric oscillator (SRO) for the mid-infrared in an output-coupled (OC) configuration, providing 17.5 W of total output power at 61% extraction efficiency. Using a single-frequency, cw Yb fiber laser at 1064 nm and a 50-mm-long MgO:PPLN crystal, through optimization of signal output coupling we generate up to 9.8 W of signal power in the near-infrared together with 7.7 W of idler power for 28.6 W of pump, while in the absence of output coupling, 8.6 W of idler power is generated for the same pump power at 30% efficiency. The SRO is tunable over 360 nm in the idler range. The deployment of signal output coupling results in a total tuning of 513 nm (120 nm of signal, 393 nm of idler) over which watt-level output power can be extracted. Through careful control of thermal effects we achieve a long-term peak-to-peak idler power stability of 5% over 14 hours near room temperature. The output beams have TEM₀₀ spatial profile with M ²<1.28 for the idler and M ²<1.37 for the signal.     

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     

Picosecond Ti:sapphire-pumped optical parametric oscillator based on periodically poled LiNbO(3)

Periodically poled lithium niobate has been used in a singly resonant optical parametric oscillator pumped by a cw mode-locked Ti:sapphire laser. A tuning range of 1.15 to 2.4 microm was achieved when the pump was tuned, and this range was limited only by the mirror reflection bandwidth. Thresholds as low as 18 mW and an overall slope efficiency of 44% were observed, with average output powers of 130 mW (70 mW) for the signal (idler).     

High-power picosecond LiB3O5 optical parametric oscillators tunable in the blue spectral range

The paper reports on an experimental investigation and numerical analysis of noncritically and critically phasematched LiB₃O₅ (LBO) optical parametric oscillators (OPOs) synchronously pumped by the third harmonic of a cw diode-pumped mode-locked Nd:YVO₄ oscillator–amplifier system. The laser system generates 9.0 W of 355-nm mode-locked radiation with a pulse duration of 7.5 ps and a repetition rate of 84 MHz. The LBO OPO, synchronously pumped by the 355-nm pulses, generates a signal wave tunable in the blue spectral range 457–479 nm. With a power of up to 5.0 W at 462 nm and 1.7 W at 1535 nm the conversion efficiency is 74%. The OPO is characterized experimentally by measuring the output power (and its dependence on the pump power, the transmission of the output coupler and the resonator length) and the pulse properties (such as pulse duration and spectral width). Also the beam quality of the resonant and nonresonant waves is investigated. The measured results are compared with the predictions of a numerical analysis for Gaussian laser and OPO beams. In addition to the blue-signal output visible-red 629-nm radiation is generated by sum-frequency mixing of the 1.535-μm infrared idler wave with the residual 1.064-μm laser radiation. A power of 1.25 W of 1.535-μm idler radiation and 5.7 W of 1.064-μm laser light generated a red 629-nm output power of 2.25 W. Received: 2 February 2000 / Revised version: 28 July 2000 / Published online: 22 November 2000     

Toward an optical synthesizer: a single-frequency parametric oscillator using periodically poled LiNbO(3)

We demonstrate single-frequency operation of a cw quasi-phase-matched singly resonant optical parametric oscillator (SRO). We obtained widely tunable output from 1.66 to 1.99 mum (signal) and from 2.29 to 2.96 mum (idler) by employing a periodically poled lithium niobate multigrating chip. Using a single-frequency miniature Nd:YAG ring laser as a pump source results in SRO output with high spectral purity and frequency stability(<10 MHz/min), which can be continuously tuned over 2 GHz without mode hops. We obtain a minimum SRO threshold of 260mW by resonating the pump wave in the SRO cavity.     

Synchronously pumped optical parametric oscillators

Recent work on the development of high-repetition-rate, synchronously pumped picosecond and femtosecond Optical Parametric Oscillators (OPOs) is reviewed. With KTP, BBO or LBO crystals and solid-state pumps such as cw mode-locked Ti:Sapphire, Nd:YAG or Nd:YLF lasers, the singly resonant OPOs or their nonlinear optical accessories yield pulses as short as 40 fs, average powers up to hundreds of milliwatts, and tunability from 200 nm to > 10 µm.     

Idler-resonant optical parametric oscillator based on KTiOAsO4

An idler-resonant KTiOAsO₄ (KTA) optical parametric oscillator is demonstrated within a diode-end-pumped acousto-optically Q-switched Nd:YAG laser. With an X-cut KTA crystal, idler wave at 3467 nm and signal wave at 1535 nm are generated. Under an incident diode pump power of 15.4 W, the idler output power of 105 mW and signal power of 720 mW are obtained at a pulse repetition rate of 40 kHz. The pulse widths of the idler and signal waves are 7.2 and 3.1 ns, respectively. The beam quality factors (M²) of the idler wave are within 1.2 in both horizontal and vertical directions.     

Continuous-wave operation of a single-frequency optical parametric oscillator at 4-5 microm based on periodically poled LiNbO3

We present a cw, Nd:YAG-pumped singly resonant single-frequency narrow-linewidth high-power optical parametric oscillator with idler tuning from 3.7 to 4.7 microm. In this spectral range the absorption of the idler wave in the LiNbO3 crystal is significant, causing the oscillation threshold to increase with a subsequent decrease in output power from 1.2 W at 3.9 microm to 120 mW at 4.7 microm. The optical parametric oscillator's cavity was stabilized and mode-hop tuned with a rotatable solid etalon but with a subsequent reduction in idler power of as much as 50%. We demonstrated the usefulness for spectroscopy by recording the photoacoustic spectrum of a strong CO2 absorption, using a 24-GHz continuous idler scan.     

利用准相位匹配光学参量振荡器获得可调谐强度差压缩光

利用106μm全固化单频Nd:YVO4激光器抽运由PPLN构建的三共振光学参量振荡器，在光学参量振荡器近简并运转的情况下：信号光和闲置光的波长相差约为200nm，观察到了信号光和闲置光的强度起伏的关联，实测强度差噪声压缩度达04dB.在此基础上，利用温度调谐了信号光和闲置光的波长，在17nm的范围内都观察到信号光和闲置光的强度起伏的关联. 关键词： 准相位匹配 光学参量振荡 强度差噪声压缩     

High-power, continuous-wave, mid-infrared optical parametric oscillator based on MgO:sPPLT

We report a stable, high-power, cw, mid-IR optical parametric oscillator using MgO-doped stoichiometric periodically poled LiTaO? (MgO:sPPLT) pumped by a Yb fiber laser at 1064 nm. The singly resonant oscillator (SRO), based on a 30 mm long crystal, is tunable over 430 nm from 3032 to 3462 nm and can generate as much as 5.5 W of mid-IR output power, with >4 W of over 60% of the tuning range and under reduced thermal effects, enabling room temperature operation. Idler power scaling measurements at ~3.3 μm are compared with an MgO-doped periodically poled LiNbO? cw SRO, confirming that MgO:sPPLT is an attractive material for multiwatt mid-IR generation. The idler output at 3299 nm exhibits a peak-to-peak power stability better than 12.8% over 5 h and frequency stability of ~1 GHz, while operating close to room temperature, and has a linewidth of ~0.2 nm, limited by the resolution of the wavemeter. The corresponding signal linewidth at 1570 nm is ~21 MHz.     

Periodic mode hopping induced by thermo-optic effects in continuous-wave optical parametric oscillators

We show that thermal effects can lead to periodic mode hopping in cw optical parametric oscillators (OPOs). This mode hopping may occur as soon as two modes have different intensities at the point where they exchange their stability; this condition is easily fulfilled in OPOs that are triply resonant, or doubly resonant with a weakly resonant pump. We have observed such oscillations experimentally in a type II OPO in both configurations. A simple thermo-optic multimode model reproduces well the experimental regimes. We expect that multimode instabilities based on this mechanism can be observed with various aspects in many experimental setups at high pumping rate.     

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.     

Green-pumped cw singly resonant optical parametric oscillator based on MgO:PPLN with frequency stabilization to an atomic resonance

We report on a green-pumped continuous-wave singly resonant optical parametric oscillator (cw SRO) based on MgO-doped periodically poled LiNbO₃. Operating the SRO at crystal temperatures between 40.0°C to 80.0°C an idler wavelength range of 1406–1451 nm can be accessed. The system provides stable single-frequency idler radiation of more than 300 mW at a pump power of 2 W while featuring a low threshold (<1.2 W). Above a pump power of 2.1 W we observe multimode operation, which is similar to the behavior reported for infrared-pumped SROs. To show the applicability of the device we demonstrate Doppler-free saturation spectroscopy of the cesium D₂ line using the signal wave and frequency stabilization to a crossover resonance of the D₂ transition.