Optical Parametric Oscillator Cavity Research Articles

Compact wavelength tunable output around 440 nm pulsed laser for oceanic lidar application

A single-resonant BBO-based optical parametric oscillator (OPO) with 27 nm tuning range in deep-blue spectral band around 440 nm was developed. Pumped by a 355 nm ultraviolet laser with 4.9 mJ pulse energy at 100 Hz repetition rate, maximum pulse energy of 1.32 mJ at 441.4 nm wavelength, corresponding to more than 0.26 MW peak power, was successfully obtained from a plano-concave OPO cavity with an about 35% output coupler, the optical–optical​ conversion efficiency was up to 26.9%. The pulse width was around 5.0 ns, and the spectral linewidth was about 0.09 nm. When the output wavelength was tuned to the Fraunhofer lines of 440.5 nm and 438.4 nm, the pulse energy of 1.27 mJ and 1.15 mJ was obtained respectively with linewidth of both about 0.07 nm, well-matched to the corresponding Fraunhofer linewidth.

Controlled Generation of Wavelength-Tunable Higher Order Poincaré Sphere Beams From a Femtosecond Optical Parametric Oscillator

Although higher order Poincaré (HOP) beams are attractive due to their unique advantages and various efforts have been made for the generation of HOP sphere beams, the current generation technologies suffer from both limited output power and narrow bandwidth, preventing further practical applications. In this paper, we report on a femtosecond optical parametric oscillator (OPO) which can deliver high average power, on-demand arbitrary HOP sphere beams tunable across a wide spectral range in the near-infrared. The desired beam mode can be achieved by manipulating the geometric phase inside the OPO cavity to map the polarization to orbital angular momentum (OAM). Pumped by a Gaussian beam from an Yb-fiber laser, the generalized vector vortex femtosecond signal beams with spectral coverage from 1367 to 1650 nm are obtained. The device can produce over 200 mW structured beam signal power cross the complete tuning range with as much as 377 mW at 1480 nm for 2 W of input pump power. The proposed configuration, which shows superiorities of high average output power, flexible wavelength tunability and complete mode controlling property, may have direct implications in applications such as quantum optics and material processing.

Compact harmonic cavity optical parametric oscillator for optical parametric amplifier seeding.

We present a broadly tunable highly efficient frequency conversion scheme, based on a low-threshold harmonic cavity optical parametric oscillator (OPO) followed by an idler-seeded power amplifier. By choosing the cavity length of the OPO equal to the 10th harmonic of its 41 MHz Yb:KGW solid-state pump laser, a very compact optical setup is achieved. A singly-resonant cavity without output coupler results in a low oscillation threshold of only 28-100 mW in the entire signal tuning range of 1.37-1.8 µm. The 2.4-4.15 µm idler radiation is coupled out at the 41 MHz pump frequency and employed to seed a post amplifier with nearly Watt-level output power. In addition, the seeder plus power amplifier concept results in clean signal and idler pulses at the fundamental repetition rate of 41 MHz with a time-bandwidth product below 0.4 and a relative intensity noise 10 dB lower compared to the solid-state pump laser.

Enhanced spectral broadening in an optical parametric oscillator based on a PPLN crystal.

We report a chirped-pulse optical parametric oscillator (OPO) generating light pulses with an instantaneous-bandwidth much wider than the parametric gain-bandwidth of nonlinear crystals. Our numerical simulations show that a relatively high residual second-order-dispersion within the OPO cavity is required in order to achieve the maximum signal-bandwidth from an OPO system. Based on this principle, we constructed an OPO using a 3-mm-long PPLN crystal, which produced a signal wave with an instantaneous-bandwidth of 20 THz (at -20 dB) covering 1447-1600 nm, roughly twice as much as the phase-matching bandwidth of the nonlinear crystal. This scheme represents a promising technical route for generating high-repetition-rate, ultrashort optical pulses with a wide bandwidth at various wavelengths, which may benefit many applications, including optical coherence tomography, pulse synthesis and spectroscopy.

Dither-free stabilization of a femtosecond doubly resonant OPO using parasitic sum-frequency mixing.

Stable operation of a doubly resonant femtosecond optical parametric oscillator (OPO) requires submicron matching of the OPO and pump laser cavity lengths, which is normally implemented using a dither-locking feedback scheme. Here we show that parasitic sum-frequency mixing between the pump and resonant pulses of a degenerate femtosecond OPO provides an error signal suitable for actuating the cavity length with the precision needed to maintain oscillation on a single fringe and at maximum output power. Unlike commonly used dither-locking approaches, the method introduces no modulation noise and requires no additional optical components, except for one narrowband filter. The scheme is demonstrated on a Ti:sapphire-pumped sub-40-fs PPKTP OPO, from which data are presented showing a tenfold reduction in relative intensity noise compared with dither locking.

绿光泵浦的黄光波段可调谐窄线宽光学参量振荡器

A pulsed optical parametric oscillator (OPO) was demonstrated for the purpose of wavelength-tunable yellow output with narrow spectral line width. The OPO pumped by the green output of an acousto-optic Q-switched Nd:YAG used a type II phase-matched KTiOPO4 (KTP) crystal as the nonlinear gain medium and a folded cavity arrangement. The OPO was designed to have the idler wave tunable in near infrared oscillated in the cavity, which was further frequency doubled to generate the wavelength-tunable yellow output by using a LiB3O5 (LBO) crystal with type I non-critical phase matching scheme. A fused silica etalon was inserted in the idler wave cavity to narrow the idler wave and the resultant yellow spectral line width. The wavelength of the yellow output obtained could be tuned over 587.2-595.2 nm, within which the maximum average output power of 2.89 W was obtained at 591.2 nm, under an incident average green pump power of 24.0 W. The beam quality factor M2 was 3.4. The conversion efficiency from the green pump to the yellow output was 12.0%. The pulse width at the maximum output power was 37 ns, and the peak power was 7.8 kW. The spectral line width of the yellow output was 0.15 nm, which was narrowed effectively compared with that without etalon in the OPO cavity.

First Steps of Maturation Towards Space of Nested Cavity Optical Parametric Oscillator and Amplifiers for DIAL Based on Periodically Poled Nonlinear Materials

We report on the first steps of maturation towards space of a nested cavity optical parametric oscillator and amplifiers, based on periodically poled nonlinear materials, emitting in the 2µm range for multi species differential absorption lidar (DIAL).

High-power femtosecond cylindrical vector beam optical parametric oscillator.

We report on high-power femtosecond cylindrical vector beam (CVB) generation from a Gaussian-pumped optical parametric oscillator (OPO). By introducing a half waveplate and a vortex half-wave plate of m = 1 to realize intracavity polarization modulation to the resonant Gaussian signal, the OPO could deliver broadband signal beam in CVB profile, i.e., radially and azimuthally polarized beam profile. The central wavelength of the generated CVB signals can be tuned continuously from 1405 to 1601 nm, while the corresponding pulse durations are all around 150 fs. A maximum average output power of 614 mW at 1505 nm is obtained. Moreover, our OPO cavity design can be extended to generate high order CVB by simply changing the vortex half-wave plate with different orders. Such a high-power CVB OPO configuration has the advantages of flexible control and wide tuning range, making it a practical tool for applications in super-resolution imaging, optical communication and quantum correlations.

Yb-fiber-pumped, high-beam-quality, idler-resonant mid-infrared picosecond optical parametric oscillator.

We report an Yb-fiber-pumped picosecond optical parametric oscillator (OPO) delivering high average power in excellent beam quality throughout the mid-infrared (mid-IR). Using MgO:PPLN as the nonlinear crystal and configured as a singly-resonant oscillator in the mid-IR idler wave, the OPO provides up to 3.5 W average power in high spatial quality with M2<1.8 across a continuous tuning range of 4028-2198 nm, with M2<1.5 at 4000 nm. It can also deliver as much as 4.3 W of signal power in an output beam with M2<1.4 across 1446-2062 nm. The extracted idler exhibits a passive power stability better than 0.46% rms over 1 hour across the entire mid-IR tuning range. We have also investigated OPO cavity length detuning behavior about the zero-group-velocity-mismatch crossing point and its effects on output power.

Tunable, dual-wavelength, single-crystal, continuous-wave optical parametric oscillator∗∗This work was supported by Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology, Electronic Countermeasure Institute, National University of Defense Technology (SKL2017KF04).

We demonstrated tunable, dual-wavelength (DW), continuous-wave mid-infrared generation in single-PPLN-based optical parametric oscillator (OPO) which was pumped by a DW Raman fiber laser located at 1060 and 1110 nm. Based on a singly resonant oscillator design, this device permits access to arbitrary signal and idler wavelength combinations within the parametric gain bandwidth and reflectivity of the OPO cavity mirrors. By tuning PPLN temperature, two pairs of signal and idler beams were obtained with arbitrary tuning across 1607–1626 nm and 3081–3583 nm. The frequency separation in the resonant signal waves was down to 5.7 THz. Moreover, near wavelength-matched condition, energy coupling between the resonant signal waves, resulted in reduced operation threshold and increased output power. A total DW output power (>6.8 W) is obtained. The experiment results exhibited great potential in mid-infrared generation using low-power pump beam with special characteristics.

Broadband tuning of ring-type cavity-dumped femtosecond optical parametric oscillator in the near-infrared.

We report a cavity-dumped optical parametric oscillator (OPO) with a ring-type cavity configuration, which is based on periodically poled lithium niobate gain synchronously pumped by a mode-locked Ti:sapphire laser. Because of reduced cavity loss and group velocity dispersion inherent to ring-cavity employment, a wide wavelength tuning capability from 1.02 to 1.65 μm was achieved by the simple displacement of a cavity mirror. At a wavelength of 1.28 μm, the cavity-dumped system provides femtosecond pulses with 42 nJ energy and 50% dumping efficiency. The group delay dispersion (GDD) of the OPO cavity could be characterized through the wavelength tuning behavior with cavity displacement, and its validity was confirmed by the numerical GDD calculation of each optical component within the cavity.

High Power 4.2-Cycle Mid-Infrared Pulses From a Self-Compression Optical Parametric Oscillator

We demonstrate the generation of few cycle mid-infrared (MIR) pulses from a self-compressed optical parametric oscillator (OPO), synchronously pumped by a 105 fs Yb3+ doped fiber laser system. By using a ring cavity design, 4.2-cycle (45.3 fs) MIR pulses at a central wavelength of 3250 nm (with a 10-dB bandwidth of 648 nm) are obtained in a simple, practical, and compact configuration. Detailed theoretical analysis and numerical simulation are performed to better understand the self-compression mechanism in such an OPO cavity. In addition, when pumped at 3.8 W, the OPO delivers idler output power up to 330 mW and the corresponding pump depletion is 74.7%.

Continuous-Wave Widely Tunable MgO:PPLN Optical Parametric Oscillator With Compact Linear Cavity

An efficient continuous-wave, widely tunable, intra-cavity optical parametric oscillator (OPO) based on periodically poled MgO:LiNbO3 (MgO:PPLN) with a compact three-mirror linear cavity was demonstrated. The mode radii of fundamental and OPO cavities with plane and concave mirrors were calculated and theoretically compared. The result shows that the fundamental laser beam could be compressed, and its power density on the MgO:PPLN crystal could be improved by optimizing concave radii of cavity mirrors. Meanwhile, better mode matching between fundamental cavity and OPO cavity could be realized. A widely tunable signal spectrum from 1.43 to $1.79~\mu \text{m}$ and an idler spectrum from 2.62 to $4.16~\mu \text{m}$ were achieved as the OPO system derived by a diode laser end-pumped Nd:YVO4 crystal laser at 1064 nm. The maximum total output power up to 6.35 W (signal output power of about 4.24 W at $1.60~\mu \text{m}$ and idler output power of about 2.11 W at $3.17~\mu \text{m}$ ) and conversion efficiency of 31.6% were obtained at an incident pump power of 20.1 W.

Efficient intra-cavity continuous-wave periodically poled lithium niobate-doped MgO optical parametric oscillator with compact V-type cavity

A compact efficient intra-cavity singly resonant optical parametric oscillator (OPO) based on periodically poled lithium niobate-doped MgO (MgO:PPLN) was investigated. A concave–concave fundamental cavity was used for focusing the fundamental beam waist on MgO:PPLN crystal, which enables more compact setup and less insertion loss than traditional insertion of a focusing lens. Two V-type OPO cavities with single and double outputs were used for comparison with idler light outputting from one and both end mirrors, respectively. The results show that the double outputs configuration achieved higher output power for its advantage of reducing the reversed OPO process and diffraction loss of the idler light. Under an incident pump power of 12.4 W, a maximum signal output power of 2.89 W at 1549 nm and total idler output power of 1.44 W at 3394 nm were obtained with a total conversion efficiency up to 34.9%.

Threshold decrease in intracavity optical parametric oscillator synchronously pumped by mode-locked laser

An intracavity optical parametric oscillator (IOPO) pumped by a continuous-wave (CW) mode-locked laser is experimentally realized. The fundamental cavity and optical parametric oscillator cavity are designed to satisfy synchronous pumping. The output characteristics of signal and idle light are measured. Because of higher fundamental photon intensity in IOPO, the threshold of IOPO is lower than that of an extra-cavity optical parametric oscillator. The spectroscopy of signal light is obtained and the wavelength of idle light can be estimated to be 3.298 μm from noncritical phase matching. Based on the intensity fluctuation mechanism of fundamental locking, the dynamical model for IOPO pumped by a CW mode-locked laser is developed. The simulated results for the temporal shape of three lights are calculated from the derived rate equations. Because of dispersion, the signal pulse width of the theory is smaller than that of the experiment with the same pump energy.

THERMAL EFFECTS IN THE EYE-SAFE RING OPTICAL PARAMETRIC OSCILLATOR BASED ON KTiOPO4 CRYSTALS

For an eye-safe optical parametric oscillator (OPO) built on the basis of a three-mirror ring cavity, each section of which (the space between adjacent plane mirrors) contains a x-cut KTiOPO4 (KТР) crystal having a size of 15(х) × 7(y) × 7(z) mm3, the thermal effects due to idler wave absorption in KTP crystals were investigated. These thermal effects were evaluated by means of experimental measurement of the change in the OPO performance (divergence of the output beam and pulse energy) when transferring the OPO from the mode of generation of occasional single pulses to the mo de of generation of periodically repetitive pulses. It was found when the eye-safe OPO pumped by multimode YAG: Nd laser radiation generates 8-ns pulses with a repetition rate of 10 Hz and an energy of 30–35 mJ, thermal distortions of KTP crystals placed in metal holders at their natural air-cooling, are moderate. The total effect of positive thermolenses induced in nonlinear crystals leads to an increase in the divergence of the beam of the eye-safe OPO by 10 % and to a decrease in the efficiency of the OPO by 0.76 %, by virtue of fact that the induced thermal lenses are not ideal and thereby introduce additional aberration losses into the OPO cavity. The theoretical simulation of the OPO operation in the plane-wave approximation with the use of a system of three coupled first-order abridged differential equations showed that among three KTP crystals the KTP crystal placed first in the path of pump radiation in the OPO is the largest thermal load and the action of the most intense beams.

Frequency Stabilization of Pulsed Injection-Seeded OPO Based on Optical Heterodyne Technique**Supported by the National Key Research and Development Program of China under Grant No 2016YFC1400902, the National Natural Science Foundation of China under Grant Nos 61505230 and 61475170, and the Shanghai Natural Science Foundation under Grant No 15ZR1445000.

A frequency stabilizing system for a pulsed injection seeded 1550nm optical parametric oscillator (OPO) at 20 Hz repetition rate is demonstrated. The optical heterodyne method is used to measure the frequency difference between the seed laser and the OPO output. Using the frequency difference as the error signal, a proportionalintegral controller in combination with a scanner is applied to stably match the OPO cavity length to the seed laser frequency. The root-mean-square (rms) error of the frequency discrimination method is <0.07MHz according to a ‘frequency shifting-chopping-beat’ evaluation. The frequency fluctuation of the frequency-stabilized OPO is 0.29MHz (rms), and the Allan deviation is less than 20 kHz for averaging time of more than 3 s.

Atmospheric boundary layer CO2 remote sensing with a direct detection LIDAR instrument based on a widely tunable optical parametric source.

We report on the capability of a direct detection differential absorption lidar (DIAL) for range resolved and integrated path (IPDIAL) remote sensing of CO2 in the atmospheric boundary layer (ABL). The laser source is an amplified nested cavity optical parametric oscillator (NesCOPO) emitting approximately 8mJ at the two measurement wavelengths selected near 2050nm. Direct detection atmospheric measurements are taken from the ground using a 30Hz frequency switching between emitted wavelengths. Results show that comparable precision measurements are achieved in DIAL and IPDIAL modes (not better than a few ppm) on high SNR targets such as near range ABL aerosol and clouds, respectively. Instrumental limitations are analyzed and degradation due to cloud scattering variability is discussed to explain observed DIAL and IPDIAL limitations.

Injection-seeded single frequency 2.05 μm output by ring cavity optical parametric oscillator

An injection-seeded single-resonant optical parametric oscillator (SROPO) with single frequency nanosecond pulsed 2.05 μm wavelength output is presented. Based on two potassium titanyl phosphate crystals and pumped by a 1064 nm single frequency laser pulse, injection seeding is performed successfully by using the ramp-hold-fire technique in a ring cavity with a bow-tie configuration. The SROPO provides 2.65 mJ single frequency signal pulse output with a 17.6 ns pulse duration at a 20 Hz repetition rate. A near-diffraction-limited beam is achieved with a beam quality factor M2 of about 1.2. The spectrum linewidth of the signal pulse is around 26.4 MHz, which is almost the Fourier-transform-limited value.

Harmonically pumped femtosecond optical parametric oscillator with multi-gigahertz repetition rate.

We report a multi-gigahertz (GHz) repetition-rate femtosecond MgO:PPLN optical parametric oscillator (OPO) harmonically pumped by a 75.6 MHz Kerr-lens mode-locked Yb:KGW laser. By fractionally increasing the OPO cavity length, we obtained OPO operation up to the 493rd harmonic of the pump laser repetition rate, corresponding to a repetition rate as high as 37.3 GHz. Using a 1.5% output coupler, we are able to extract signal pulses with up to 260 mW average power at the 102nd harmonic (7.7 GHz) and 90 mW at the 493rd harmonic (37.3 GHz) under 2 W pump power. The measured relative standard deviations of the fundamental and the 102nd harmonic signal power were recorded to be 0.5% and 2.1%, respectively. The signal pulse durations at different harmonics were measured in the range of 160-230 fs.