High-power Optical Parametric Oscillator Research Articles

51-W average power, 169-fs pulses from an ultrafast non-collinear optical parametric oscillator.

We present a high power optical parametric oscillator (OPO) synchronously pumped by the second-harmonic of a modelocked 1030-nm thin-disk laser (TDL) oscillator. The OPO delivers an average power of 51.1 W around degeneracy (1030 nm) with a 10.2-MHz repetition-rate. After extra-cavity dispersion compensation using dispersive mirrors, we obtain a pulse duration of 169 fs, which is 4.6× shorter than the TDL pulse duration of 770 fs. The TDL has 250W average power, which is converted to 215W at the second-harmonic. Hence, the OPO exhibits a high photon conversion efficiency of 47% (ratio of signal photons to 515-nm pump photons). Moreover, the OPO generates a peak power of 26.2 MW, which is very similar to the 28.0-MW peak power of the TDL. To facilitate continuous tuning around degeneracy and convenient extraction of the pump and idler beams, the OPO is operated in a noncollinear configuration. A linear cavity configuration was chosen since it offers easy alignment and straightforward cavity length tuning. To the best of our knowledge, this source has the highest average power generated by any ultrafast OPO, and the shortest pulse duration for any >5-W OPO. This result is an important step to adding wavelength tunability to high power Yb-based laser sources without the complexity of either laser or parametric amplifier systems.

Theoretical study on thermal characteristic of MgO: PPLN crystal in high power optical parametric oscillator

This study focuses on the thermal characteristic of an end-pumped MgO: PPLN crystal by solving the transient temperature evolution model in a high power optical parametric oscillator. In this model, an approach based on contact mechanics theory is proposed to quantitatively calculate the heat transfer between rough contacting surfaces of crystal and heat sink. Based on the model, a parametric study has been performed to investigate the influence of the heat sink property, pump laserand crystal dimension on the thermal characteristic of the laser crystal. Obtained results reveal a closed correlation between the mentioned parameters and the thermal characteristic of the crystal indicating that a proper selection of the parameters is essential to control the crystal temperature and improve the performance of the laser.

水汽差分吸收激光雷达发射机935 nm高功率光参量振荡器

水汽差分吸收激光雷达发射机935 nm高功率光参量振荡器

High-power optical parametric oscillator based on a high-pulse repetition rate, master Nd : KGW laser

An optical scheme of an optical parametric oscillator with a master laser based on an Nd : KGW active element excited by two orthogonally oriented diode side pump modules is proposed to form radiation pulses with energies above 30 mJ and a repetition rate of 1 – 20 Hz in the eye-safe spectral range of 1.5 – 1.6 μm. The two-module excitation of the active medium makes the distribution of the master laser radiation intensity in the output beam cross section more uniform and provides a reliable operation of the optical parametric oscillator.

Numerical study of high-energy optical parametric oscillator with top-hat pump intensity profile and quasi-phase-matched crystal with wedge-shaped domain

We present a numerical study for the design of efficient MgO :PPLN based pulsed nanosecond optical parametric oscillator (OPO), with input pump pulses of top-hat transverse intensity profile, and a double-pass pump cavity configuration. In particular, we investigate the effect of domain shape on the conversion efficiency. We considered two types of domain structures: "perfect vertical-wall" and "wedge-shaped" domains and our numerical results show that at higher pump pulse energies, the conversion efficiency saturates, and the saturated efficiency is almost independent of the domain shapes. Based on our study, we also propose a new scheme for development of compact high-power OPO sources using MgO :PPLN chips of relatively short lengths and large cross-sectional area.

High-precision and high-accuracy rovibrational spectroscopy of molecular ions

We present a versatile new instrument capable of measuring rovibrational transition frequencies of molecular ions with sub-MHz accuracy and precision. A liquid-nitrogen cooled positive column discharge cell, which can produce large column densities of a wide variety of molecular ions, is probed with sub-Doppler spectroscopy enabled by a high-power optical parametric oscillator locked to a moderate finesse external cavity. Frequency modulation (heterodyne) spectroscopy is employed to reduce intensity fluctuations due to the cavity lock, and velocity modulation spectroscopy permits ion-neutral discrimination. The relatively narrow Lamb dips are precisely and accurately calibrated using an optical frequency comb. This method is completely general as it relies on the direct measurement of absorption or dispersion of rovibrational transitions. We expect that this new approach will open up many new possibilities: from providing new benchmarks for state-of-the-art ab initio calculations to supporting astronomical observations to helping assign congested spectra by combination differences. Herein, we describe the instrument in detail and demonstrate its performance by measuring ten R-branch transitions in the ν2 band of H3(+), two transitions in the ν1 band of HCO(+), and the first sub-Doppler transition of CH5(+).

Frequency comb assisted mid-infrared spectroscopy of cold molecular ions

A mid-infrared spectrometer consisting of a high power optical parametric oscillator, a frequency comb, and a cold ion trap is described and characterized. The idler frequency at 3 μm is measured accurately by analyzing the pump and signal beat frequencies with the comb. This is done via two spectrum analyzers, allowing for a wide and continuous scanning ideal for spectroscopy of cold molecules with unknown spectra. The potential of this approach is demonstrated by measuring a ro-vibrational line of CH(5)(+) in a 22-pole ion trap via action spectroscopy of only several thousand cold ions. The current setup limits the precision of the line center frequency determination to some 100 kHz with ample room for future improvements. Following this approach, ground state combination differences of molecular ions can be predicted in order to identify them in astronomical objects.

Large aperture PPMgLN based high-power optical parametric oscillator at 38 µm pumped by a nanosecond linearly polarized fiber MOPA

We report a large aperture PPMgLN based OPO generating 21W of average output power at a slope efficiency of 45%. The OPO is pumped with the output from a polarization maintaining Ytterbium doped fiber MOPA operating at 1060nm producing 20ns pulses at a repetition rate of 100kHz and an average output power of 58W (after the isolators). A maximum of 5.5W of optical power was recorded at the idler wavelength of 3.82µm without thermal roll-off. The pulse rise/fall time plays a significant role in the OPO conversion efficiency and that further enhancements in the efficiency should be possible using pulses with faster rise and fall times.

基于周期性畴极化反转掺镁铌酸锂晶体的脉冲光纤激光器抽运的高功率光参量振荡器

基于周期性畴极化反转掺镁铌酸锂晶体的脉冲光纤激光器抽运的高功率光参量振荡器

Characterization of single diamondlike and polymerlike nanoparticles by midinfrared nanospectroscopy

We report on the characterization of single nanoparticles produced in N2–C2H2 low pressure plasmas using scanning near-field infrared microscopy. We use a high power optical parametric oscillator as radiation source, which emits in the so-called fingerprint region 2500–3570 cm−1. We have probed the characteristic N–H absorption band at 3300 cm−1 to characterize single nanoparticles. The observed near-field contrast allows to distinguish between diamond- and polymerlike nanoparticles. Here, the term “diamondlike” refers to hard amorphous carbon material with abundant sp3-coordinated C atoms. Our results demonstrate the feasibility of an infrared spectral characterization of single nanoparticles with nanometer lateral resolution.

PPMgLN-Based High-Power Optical Parametric Oscillator Pumped by Yb $^{{\bm 3}{\bm +}}$-Doped Fiber Amplifier Incorporates Active Pulse Shaping

We report a periodically poled magnesium-oxide-doped lithium niobate (PPMgLN) based optical parametric oscillator (OPO) pumped by a diode-seeded, linearly polarized, high-power, pulsed, ytterbium fiber master oscillator power amplifier (MOPA). Using adaptive pulse shaping of the seed laser (using an external modulator), we demonstrate a reduction in the impact of dynamic gain saturation and optical Kerr/Raman nonlinearities within the fiber MOPA, obtaining shaped signal and idler pulses at the OPO output and reduced spectral bandwidths. A maximum average output power of 26.5 W was obtained from the MOPA at 1062 nm. An output power as high as 11 W from the OPO at an overall slope efficiency of 67% was achieved, with 2.7 W of output power obtained at a wavelength of 3.5 mum. Our experiments were pump-power-limited and considerable scope remains for further power scaling of such OPOs using this approach.

Overtone spectroscopy of H2D+ and D2H+ using laser induced reactions

The method of laser induced reaction is used to obtain high-resolution IR spectra of H2D+ and D2H+ in collision with n-H2 at a nominal temperature of 17 K. For this purpose three cw-laser systems have been coupled to a 22-pole ion trap apparatus, two commercial diode laser systems in the ranges of 6100-6600 cm(-1) and 6760-7300 cm(-1), respectively, and a high-power optical parametric oscillator tunable in the range of 2600-3200 cm(-1). In total, 27 new overtone and combination transitions have been detected for H2D+ and D2H+, as well as a weak line in the nu1 vibrational band of H2D+ (2(20)<--1(01)) at 3164.118 cm(-1). The line positions are compared to high accuracy ab initio calculations, showing small but mode-dependent differences, being largest for three vibrational quanta in the nu2 symmetric bending of H2D+. Within the experimental accuracy, the relative values of the ab initio predicted Einstein B coefficients are confirmed.

Green-pumped high-power optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO_3

A high-power 532 nm-pumped multikilohertz nanosecond optical parametric oscillator using a periodically poled 1.0 mol.% MgO-doped stoichiometric lithium tantalate crystal that could be operated from room temperature to 200 degrees C without damage is reported. A broad continuous tuning range from 855 to 1410 nm was achieved within a single domain period. Efficient operation of high peak power and watt level average power with a power conversion of 62.5% was measured. These results show that a high-resolution high average power visible tunable source can be realized.

Widely tunable high power OPO based on a periodically poled MgO doped lithium niobate crystal

An optical parametric oscillator (OPO) based on a highly MgO doped periodically poled lithium niobate (PPMgLN) crystal was experimentally demonstrated and the result is presented in this report. The PPMgLN wafer was fabricated from a MgO doped (with 6 mol% doping concentration) lithium niobate crystal by means of high voltage pulse trigged domain reversal technique and has 20 domain reversal periods from 27.8 to 31.6 μ m with a step of 0.2 μ m between the neighbor periods. An acousto-optic (AO) Q-switched Nd 3 + : YVO 4 laser was used as the pumping laser. A maximum laser output power of 4.8 W has been achieved for the OPO when the pumping power is 10.8 W and it corresponds to an optic-optic conversion efficiency of 44%. By shifting the PPMgLN wafer, the periods of the domain structure on the PPMgLN wafer can be changed, thus enabling a wide spectral tuning range of the laser output from 1.42 to 1.73 μ m (for the signal light) and from 2.76 to 4.27 μ m (for the idler light).

Continuous-wave operation of a single-frequency optical parametric oscillator at 4–5 μm based on periodically poled LiNbO_3

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.

High-power optical parametric oscillation in large-aperture periodically poled KTiOPO_4

Electric field poling has been employed to fabricate 3-mm-thick periodically poled KTiOPO>(4) crystal for a high-power optical parametric oscillator. The maximum output power of the singly resonant optical parametric oscillator reached 13 mJ with 45% efficiency when the resonator was pumped with a 2.2-mm-diameter beam from a Q-switched Nd:YAG laser. The influence of the cavity design on the spectral and spatial qualities of the output parametric radiation is also discussed.

Tunable high-power urea optical parametric oscillator

A tunable, high-power optical parametric oscillator (OPO), using a urea single crystal as the nonlinear medium, is described. This OPO may be tuned from 506 to 900 nm when pumped with the 355-nm output of a frequency-tripled, Q-switched Nd:YAG laser. An average power of 50 mW has been achieved, with conversion efficiencies exceeding 20% at 530 nm. The feasibility of increasing the average power to greater than 100 mW was demonstrated. High efficiency can be maintained while pumping with the near field of the Nd:YAG laser. The urea OPO is a compact, solid-state device that could be used for most laser applications requiring tunability between 500 and 1225 nm. The demonstrated high-peak power could provide efficient doubling or mixing into the 250-500-nm region, thus providing a convenient solid-state device for producing laser radiation from the UV to the near IR. Applications include spectroscopy, medicine, materials processing, nonlinear optics, and laser photochemistry. >