Cw Optical Parametric Oscillator Research Articles

Widely tunable room-temperature green-pumped continuous-wave optical parametric oscillator from the red to mid-infrared

We report, to the best of our knowledge, the first realization of a room-temperature green-pumped continuous-wave (cw) optical parametric oscillator (OPO), providing wide and rapid tunability directly from the red to mid-infrared. The OPO, based on fanout MgO:sPPLT crystal and pumped at 532 nm, can provide a total signal and idler wavelength tuning range over 2554 nm, from 638 to 3192 nm. By deploying finite output coupling of the resonant wave at room temperature, also for the first time, to the best of our knowledge, we achieve enhanced output power and extraction efficiency, with the OPO delivering 4.6 W of total output power with pump depletion of 75% and total external efficiency as high as 50%. We believe 638 nm is the shortest signal wavelength generated from a cw green-pumped OPO in any fanout-grating nonlinear material to date. The passive power and frequency stability, linewidth, spatial beam profile, and beam pointing stability of the output-coupled signal, which are crucial for many applications, have been studied.

CW optical parametric oscillator for the mid-IR range

We report the development of a cw optical parametric oscillator (OPO) for the mid-IR range. The oscillator uses a 50-mm long periodically poled lithium niobate crystal in a ring resonator. The OPO is pumped by an ytterbium fibre laser with a wavelength of 1.064 μm. At a pump power of 10 W, the OPO generates continuous radiation with a wavelength of 3.6 μm and a power of 2.8 W. The pump power depletion in the OPO is 94 %. The idler wave frequency of the OPO is stabilised using a precision laser wavelength meter. The rms error of the idler wave frequency in the stabilisation regime is 3 MHz. A simple theoretical model for the operation of a cw OPO is proposed, based on an empirical characteristic of the OPO, i.e., the pump depletion, and on a quantum description of three interacting light waves. The power characteristics of the operating OPO are in good agreement with those predicted by the theoretical model.

Broadly tunable, intracavity injection-seeded, hybrid optical parametric oscillator

We report a novel, to the best of our knowledge, approach for injection seeding of pulsed optical parametric oscillators (OPOs), which can provide spectral control over the full tuning range. Bandwidth reduction down to single-mode operation is realized across the pulsed tuning range by deploying a hybrid design, where a continuous-wave (cw) OPO injection seeds the pulsed OPO in a single composite cavity. By exploiting two identical MgO-doped periodically poled lithium niobate crystals, the hybrid OPO provides signal pulses with a single-frequency linewidth as narrow as 7.2 MHz across 1510-1677 nm. The effect of cw injection seeding on pulsed OPO operation is also confirmed by reduced rise time, increased pump depletion, major reduction in threshold, and substantial enhancement in output power and extraction efficiency.

Application of a pulsed OPO seeded by a CW OPO to investigation of linewidth effects on TALIF excitation efficiency

In this article we present a widely tunable laser architecture for high-resolution nonlinear spectroscopy which incorporates a continuous wave optical parametric oscillator (OPO) for injection-seeding of a singly resonant actively-locked β-Ba(BO2)2 nanosecond OPO. Such an instrumental configuration is designed to provide near-transform-limited pulses over 450–650 nm signal, and 225–325 nm after signal doubling. Novel features that enable frequency agility and ramp-lock injection-seeding over a wide frequency range are described. System performance was demonstrated through investigations of two-photon laser induced fluorescence (TALIF) and the influence of excitation linewidth on the signal strength of the 5p6S0 - 6p[3/2]2 transition of atomic xenon at 252.49 nm. Measurements conducted at xenon partial pressures of 1×10-1-4×10-4 Torr, with and without active cavity locking and injection seeding, resulted in a 17× increased TALIF fluorescence yield during injection-seeded operation. The results are found to be consistent with modeling, taking into account the effects of lineshape, energy, and beam spatial cross-section. Modeling was informed by direct single-shot measurements of the signal beam lineshape in seeded and free-running operation using a virtually imaged phased array (VIPA) spectrometer.

Green-pumped continuous-wave parametric oscillator based on fanout-grating MgO:PPLN.

We report the first green-pumped continuous-wave (cw) optical parametric oscillator (OPO) based on MgO:PPLN in a fanout grating design. Pumped by a single-frequency cw laser at 532 nm, the OPO provides tunable radiation across 813-1032 nm in the signal and 1098-1539 nm in the idler by simple mechanical translation at a fixed temperature of 55°C. By deploying a 25-mm-long crystal to minimize thermal effects and using output coupling for the signal wave, we generate a total output power of up to 714 mW at 30% extraction efficiency in excellent Gaussian beam quality with M2<1.1 and high output stability. Simultaneous measurements of signal and idler power result in passive stability of 2.8% and 1.8% rms, respectively, over 1 h. Strong thermal effects contribute to the high stability and excellent beam quality, while linear and green-induced infrared absorption limit the power scaling capabilities of the OPO. The output signal is single-mode with an instantaneous linewidth of ∼3MHz and frequency stability of ∼84MHz over 72 s.

All-fiber CW optical parametric oscillator tuned from 1642.5 to 1655.4 nm by a low-loss SMS filter

A continuous-wave tunable all-fiber optical parametric oscillator (FOPO) was demonstrated with a single-mode–multimode–single-mode (SMS) device used as wavelength selection filter. A highly nonlinear fiber (HNLF) was used to provide nonlinear gain, and two cascaded SMS fiber structures, having low insertion losses and containing multimode fibers of different lengths and core diameters, were used for effective wavelength selection. The maximum FOPO signal power was 0.5 W at 1642.5 nm, with 2 W of pump light incident on the HNLF end face. The power stability of the FOPO signal output was better than 0.2 dB over 30 min. A wavelength tuning range from 1642.5 to 1655.4 nm was realized by stretching a multimode fiber in the SMS device.

Tunable ultraviolet vortex source based on a continuous-wave optical parametric oscillator

We report a continuous-wave (cw) optical parametric oscillator (OPO) generating optical vortices tunable in the ultraviolet (UV). Based on MgO:sPPLT as the nonlinear crystal, the singly resonant OPO is pumped by a cw vortex beam in the green, and deploying intracavity sum-frequency generation (SFG) between the undepleted pump and the Gaussian resonant signal in the crystal of BiB3O6, it can generate optical vortices of order, luv=1 and 2, tunable across 332-344nm in the UV with a maximum power of 12mW. Due to conservation of orbital angular momentum in the parametric process, the OPO also produces a non-resonant idler output beam in a vortex spatial profile of order li=1 and 2, identical to the pump vortex, with the signal beam in Gaussian distribution. The idler vortex is tunable across 1172-1338nm with maximum output power of 1.3W.

Widely tunable room-temperature continuous-wave optical parametric oscillator based on periodically-poled KTiOPO4.

We report the first realization of widely tunable continuous-wave (cw) optical parametric oscillator (OPO) based on periodically-poled KTiOPO4 (PPKTP) at room temperature. By exploiting fan-out grating design in a 30-mm PPKTP crystal, and configured in an output-coupled singly-resonant oscillator (OC-SRO) configuration pumped at 532 nm in the green, the OPO provides finely tunable radiation across 741-922 nm in the signal and 1258-1884 nm in the idler, at a fixed temperature of 25 °C. The use of output coupling for the signal wave enables enhancement of OPO extraction efficiency to 30%, providing a maximum total output power of 1.65 W (450 mW of signal at 901 nm and 1.2 W of idler at 1299 nm) for 5.5 W of pump power. The output idler exhibits passive power stability better than 3.2% rms over >2 mins, and the extracted signal exhibits frequency stability of 194 MHz over more than 35 seconds, in excellent beam quality. The OPO performance in pure SRO configuration has also been investigated.

Focus on photonics, spectroscopy, and spectrometry

Focus on photonics, spectroscopy, and spectrometry

Made Easy: CW Laser Light Widely Tunable Across the Visible

AbstractA remarkable number of photonic applications call for continuous‐wave (cw) laser light that is widely tunable throughout the visible range of the spectrum. However, this spectral region remains difficult to access with conventional tunable laser devices. This is why recently commercialized sources based on cw optical parametric oscillator (OPO) technology gain market awareness – and become increasingly recognized as cost‐effective and user friendly turn‐key solutions.

Multimilliwatt, tunable, continuous-wave, mid-infrared generation across 4.6-4.7 μm based on orientation-patterned gallium phosphide.

We report the generation of tunable continuous-wave (cw) mid-infrared (mid-IR) radiation across 4608-4694nm using the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). By exploiting difference-frequency mixing between a cw Tm-fiber laser and a home-built cw optical parametric oscillator in a 40-mm-long crystal, we have generated up to 43mW of cw output power, with >30 mW across >95% of the mid-IR tuning range. The output at 4608nm exhibits high beam quality with a passive power stability of 2.5%rms over 1.5min. The temperature acceptance bandwidth of the OP-GaP crystal has been measured and compared with theory. The performance of the mid-IR source at high pump powers and polarization-dependent transmission in OP-GaP has been investigated.

Continuous-wave whispering-gallery optical parametric oscillator based on CdSiP2.

Continuous-wave (cw) optical parametric oscillators (OPOs) are ideally suited for applications, for example high-resolution spectroscopy, that need coherent sources combining narrow-linewidth emission with good wavelength tunability. Here, we demonstrate for the first time cw OPOs based on a millimeter-sized whispering gallery resonator (WGR) made of cadmium silicon phosphide (CdSiP2). By employing a compact laser diode at 1.57-μm wavelength for pumping, a cw OPO with wavelength tunability from 2.3 μm to 5.1 μm is realized based on such a resonator. The oscillation thresholds are in the milliwatt range. The maximum total power conversion efficiency reaches more than 15%. The intrinsic quality factor at 1.57 μm is determined to be 3.5 × 106. This work suggests that CdSiP2 is a very promising alternative for constructing mid-infrared parametric devices.

Continuous-wave, multimilliwatt, mid-infrared source tunable across 6.4-7.5 μm based on orientation-patterned GaAs.

We report a continuous-wave (cw) source of tunable mid-infrared radiation providing tens of milliwatt of output power in the 6460-7517 nm spectral range. The source is based on difference-frequency generation (DFG) in orientation-patterned (OP)-GaAs pumped by a Tm-fiber laser at 2010 nm and a 1064 nm-Yb-fiber-pumped cw optical parametric oscillator. Using a 25.7-mm-long OP-GaAs crystal, we have generated up to 51.1 mW of output power at 6790 nm, with >40 mW and >20 mW across 32% and 80% of the mid-infrared tuning range, respectively, which is to the best of our knowledge the highest tunable cw power generated in OP-GaAs in this spectral range. The DFG output at maximum power exhibits passive power stability better than 2.3% rms over more than 1 h and a frequency stability of 1.8 GHz over more than 1 min, in high spatial beam quality. The system and crystal performance at high pump powers have been studied.

Tunable, dual-wavelength interferometrically coupled continuous-wave parametric source

Generation of dual-wavelength continuous-wave (cw) radiation with independent and arbitrarily tuning, and indefinitely close spacing, using two cw optical parametric oscillators (OPOs) coupled with an anti-resonant ring interferometer is reported. The singly resonant OPOs, based on identical 30-mm-long MgO:sPPLT crystals, are pumped by a single cw laser at 532 nm. Two pairs of signal and idler wavelengths can be independently and arbitrarily tuned, with each signal (idler) pair tuned through degeneracy and beyond. Frequency separation between two distinct resonant signal waves from 7 down to 0.8 THz is demonstrated, and their overlap at 951 nm providing a frequency difference as small as ~220 MHz is shown. The OPOs independently provide a signal (idler) wavelength coverage across 870–1,000 nm (1,040–1,370 nm) and simultaneously generate idler powers of >1 W.

Tunable, continuous-wave, ultraviolet source based on intracavity sum-frequency-generation in an optical parametric oscillator using BiB_3O_6

We report a continuous-wave (cw) source of tunable radiation across 333-345 nm in the ultraviolet (UV) using bismuth triborate, BiB₃O₆ (BIBO) as the nonlinear gain material. The source is based on internal sum-frequency-generation (SFG) in a cw singly-resonant optical parametric oscillator (OPO) pumped at 532 nm. The compact tunable source employs a 30-mm-long MgO:sPPLT crystal as the OPO gain medium and a 5-mm-long BIBO crystal for intracavity SFG of the signal and pump, providing up to 21.6 mW of UV power at 339.7 nm, with >15 mW over 64% of the SFG tuning range. The cw OPO is also tunable across 1158-1312 nm in the idler, delivering as much as 1.7 W at 1247 nm, with >1W over 65% of the tuning range. The UV output at maximum power exhibits passive power stability better than 3.4% rms and frequency stability of 193 GHz over more than one minute.

宽波段连续调谐全固态CW-PPMgLN光学参量振荡器

宽波段连续调谐全固态CW-PPMgLN光学参量振荡器

High-power, continuous-wave, single-frequency, all-periodically-poled, near-infrared source

We report a high-power, single-frequency, continuous-wave (cw) source tunable across 775-807 nm in the near-infrared, based on internal second harmonic generation (SHG) of a cw singly-resonant optical parametric oscillator (OPO) pumped by a Yb-fiber laser. The compact, all-periodically-poled source employs a 48-mm-long, multigrating MgO doped periodically poled lithium niobate (MgO:PPLN) crystal for the OPO and a 30-mm-long, fan-out grating MgO-doped stoichiometric periodically poled lithium tantalate (MgO:sPPLT) crystal for intracavity SHG, providing as much as 3.7 W of near-infrared power at 793 nm, together with 4 W of idler power at 3232 nm, at an overall extraction efficiency of 28%. Further, the cw OPO is tunable across 3125-3396 nm in the idler, providing as much as 4.3 W at 3133 nm with >3.8 W over 77% of the tuning range together with >3 W of near-infrared power across 56% of SHG tuning range, in high-spatial beam-quality with M2<1.4. The SHG output has an instantaneous linewidth of 8.5 MHz and exhibits a passive power stability better than 3.5% rms over more than 1 min.

Sub-Doppler mid-infrared spectroscopy of molecular ions

The technique of velocity modulation spectroscopy has recently been combined with cavity enhancement and frequency modulation methods into a technique called noise-immune cavity-enhanced optical heterodyne velocity modulation spectroscopy (NICE-OHVMS). We have implemented NICE-OHVMS with a cw-optical parametric oscillator (OPO) tunable from 3.2 to 3.9μm, and used it to record spectra of the R(1,0) and R(1,1)u transitions of the ν2 fundamental band of H3+. The high optical power and cavity enhancement enable saturation of rovibrational transitions, which allows for line center frequencies to be measured with a precision of 70kHz.

Mode-locked, continuous-wave, singly resonant optical parametric oscillator

We report an actively mode-locked continuous-wave (cw) optical parametric oscillator in singly resonant oscillator (SRO) configuration, generating stable 230 ps pulses at 80 MHz repetition rate. The idler-resonant cw SRO, configured in standing-wave cavity, is based on MgO:sPPLT as the nonlinear gain material and pumped at 532 nm. Mode-locking is achieved by direct deployment of an intracavity phase modulator close to one of the SRO cavity end mirrors. The effects of modulation depth and modulation frequency on mode-locked pulse duration and repetition rate are investigated for both idler and signal pulses. Mode-locking is further confirmed by enhancement of single-pass second-harmonic generation of SRO output in the crystal of β-BaB(2)O(4).

A narrow-linewidth optical parametric oscillator for mid-infrared high-resolution spectroscopy

We present a narrow-linewidth, singly-resonant cw optical parametric oscillator, emitting more than 1 W in the 2.7–4.2 µm range. The OPO is pumped by a narrow linewidth (40 kHz) fibre-laser system and the signal frequency is locked to a high-finesse Fabry–Pérot cavity in order to increase the spectral resolution, thus obtaining a residual linewidth of 70 kHz for the signal. We tested the spectral performance of our OPO on several transitions in the ν1 rovibrational band of CH3I, measuring line intensities and showing sub-Doppler dip detection.