12 W mid-infrared output,singly resonant,continuous-wave optical parametric oscillator pumped by a Yb<Superscript>3+</Superscript>-doped fiber amplifier

We report a continuous-wave singly resonant optical parametric oscillator (SRO) with more than 12 W of idler power at 3414 nm when it was operated at 30°C. The SRO was directly pumped by a single-frequency, ytterbium-doped fiber laser with 49 W linear polarization pump powers, and based on 50 mm long periodically poled MgO:LiNbO₃ crystal (PPMgLN) in two-mirror linear cavity with 30.5 μm grating period. It’s pump power at threshold was 5.4 W. The slope-efficiency and quantum-limited performance reached 26 and 79.2%, respectively. The beam polarization matched the e → e + e interaction in crystal. The idler waves were temperature tuned in the range of 3654 to 3811 nm and 3248 to 3414 nm based on two 50 mm long PPMgLN with 29.5 and 30.5 μm grating period. To the best of our knowledge, this is the highest continuouswave mid-IR output obtained for a fiber laser pumped optical parametric oscillator (OPO).     

A pump-resonant signal-resonant optical parametric oscillator for spectroscopic breath analysis

We report on a widely tunable continuous-wave single-frequency pump-resonant signal-resonant optical parametric oscillator (PRSRO) delivering 20 mW to 50 mW of idler power spanning an octave bandwidth in the mid-infrared (1.7 μm and 3.5 μm). The PRSRO is pumped by a Ti:Al₂O₃ ring laser delivering 760 mW around λ _p =795 nm, and thanks to the pump enhancement a threshold as low as 110 mW is achieved with a multi-grating temperature-tuned MgO-doped periodically-poled LiNbO₃. This PRSRO will be used for multi-species trace gas sensing based on cavity ring-down spectroscopy.     

Cascaded continuous-wave singly resonant optical parametric oscillator pumped by a single-frequency fiber laser

We present a cascaded continuous-wave singly resonant optical parametric oscillator (SRO) delivering idler output in mid-IR and terahertz frequency range. The SRO was pumped by an ytterbium-doped fiber laser with 27 W linear polarization pump powers, and based on periodically poled MgO:LiNbO₃ crystal (PPMgLN) in two-mirror linear cavity. The PPMgLN is 50 mm long with 29.5 μm period. The idler power output at 3811 nm was obtained 2.6 W. The additional spectral components that have been attributed to cascaded optical parametric processes are described at increasing pump levels. Besides the initial signal component at about 1476.8 nm, further generated wavelengths with frequency shifts about 47 cm^?1, 94 cm^?1 and 104 cm^?1 were observed. It was speculated that the idler waves lie in the terahertz (THz) domain from the observed results.     

CW efficient optically-pumped far-infrared waveguide NH3 lasers

Significant improvements in both output power and threshold pump power have been obtained by using a small-bore (6- and 12-mm ID) copper waveguide cavity in a CW optically pumped FIR NH₃ laser. Conversion efficiencies of 10–20% the theoretical maximum and volumetric photon-conversion efficiencies 0.1–0.2%/cm³ are obtained for the 81.5-μm line, and threshold pump powers as low as 0.03 W at 81.5 μm and 0.06 W at 263.4 μm are reported. It is shown that both the output and the threshold can be improved by employing a longer waveguide cavity in the 5–160 cm length range. Lasing in a compact waveguide NH₃ lasers is also demonstrated.     

Low-threshold singly-resonant continuous-wave optical parametric oscillator based on MgO-doped PPLN

We present a 532 nm-pumped singly-resonant cw optical parametric oscillator based on MgO-doped PPLN with a minimum threshold pump power of 0.3 W. The OPO with a two-mirror standing-wave cavity is optimized by using a tunable diode laser on the path of the resonant signal beam. The maximum output power is 200 mW at an idler wavelength near 1330 nm at a pump power of 2 W. We report the degradation of the output power and beam characteristics at high pump power indicating a strong thermal lensing in the crystal. The continuous tuning range of the OPO is measured to be 800 MHz which is close to 90% of the free spectral range of the OPO cavity.     

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.     

Low noise, continuous-wave single-frequency 1.5-μm laser generated by a singly resonant optical parametric oscillator

We report a low noise continuous-wave (CW) single-frequency 1.5-μm laser source obtained by a singly resonant optical parametric oscillator (SRO) based on periodically poled lithium niobate (PPLN). The SRO was pumped by a CW single-frequency Nd:YVO₄ laser at 1.06 μm. The 1.02 W of CW single-frequency signal laser at 1.5 μm was obtained at pump power of 6 W. At the output power of around 0.75 W, the power stability was better than ±1.5% and no mode-hopping was observed in 30 min and frequency stability was better than 8.5 MHz in 1 min. The signal wavelength could be tuned from 1.57 to 1.59 μm by varying the PPLN temperature. The 1.5-μm laser exhibits low noise characteristics, the intensity noise of the laser reaches the shot noise limit (SNL) at an analysis frequency of 4 MHz and the phase noise is less than 1 dB above the SNL at analysis frequencies above 10 MHz.     

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.     

Spectroscopic and laser properties of Nd:Gd0.8La0.2VO4 crystal

The polarised absorption and fluorescence spectra of Nd:Gd_0.8La_0.2VO₄ crystal are measured and compared to those of Nd:GdVO₄. CW laser properties of diode-pumped Nd:Gd_0.8La_0.2VO₄ crystal operating at fundamental wavelengths of 1.06 and 1.34 μm, as well as when intracavity frequency-doubled to 532 and 670 nm, have been studied. The maximum output powers at 1.06 μm, 1.34 μm, 532 nm and 670 nm are 1.18 W, 671 mW, 206 mW and 42 mW respectively, at a diode-launched pump power of 2.9 W. The threshold pump powers are 80, 267, 7 and 15 mW respectively.     

Low-threshold mid-IR MgO:PPLN optical parametric generation with high reflectivity mirror for signal wavelength

A low-threshold middle-infrared(mid-IR) MgO:PPLN optical parametric generation(OPG)pumped by a laser diode(LDl end-pumped Z-type Nd:YLF laser at 1047 nm is realized with high reflectivity(HR) mirror for signal.At repetition rate of 10 kHz,the OPG threshold of 50μJ has been achieved with HR mirror for signal.Compared with the threshold without mirror,the threshold decreases by 17%.Using HR mirror for pump at output side of crystal,the threshold of 40μJ is achieved.The 2.7-4.1μm continuous tunable output is produced with seven grating periods from 28.5 to 31.5μm and temperatures from 30 to 200℃.When the incident average pump power is 3 W.the OPG idler output power is 0.46 W at 3.26 μm,which corresponds to optical-to-optical conversion efficiency up to 15.3%.     

Wide single-mode tuning of a 3.0- 3.8-mum, 700-mW, continuous-wave Nd:YAG-pumped optical parametric oscillator based on periodically poled lithium niobate

A new optical parametric oscillator (OPO) for the mid-infrared wavelength region of 3-3.8mum with an idler output power of up to 1.5 W has been developed. The singly resonant OPO is pumped by a single-mode, 10-W, continuous-wave Nd:YAG laser and consists of a bow-tie ring cavity with a fan-out periodically poled lithium niobate crystal and a low-finesse intracavity air-spaced etalon. The single-frequency idler output can be continuously tuned over 24 GHz with 700-mW power by tuning of the pump laser. The tuning was demonstrated by recording of an absorption line of ethane with photoacoustic spectroscopy.     

CW mode locked Nd:YVO4 laser pumped by 20-W laser diode bar

The efficient cw mode locking (cw-ML) regime was demonstrated in Nd:YVO₄ laser by means of saturable absorber mirror (SAM). The 0.3-at.% Nd³⁺ doped 10-mm-long YVO₄ crystal end pumped by 20-W diode module with a beam shaper was applied as a gain medium located in the close vicinity to the rear flat mirror of the first arm of Z-type resonator of 316 cm total length with two curved mirrors of 100-cm curvature radii. The SAM of 2%-saturable absorptance and saturation fluence of 50 μJ/cm² was mounted at the opposite end of a resonator. The developed “dynamically stable” cavity design mitigates detrimental role of thermal aberration in gain medium, enforcing clean perfect mode locking even for the highest pump densities. The cw-ML pulses with 47.5 MHz repetition rate and pulse durations in the range of 15–20 ps were observed for a wide range of pump powers and output coupler losses. In the best case, for 32% of output coupler transmission, up to 6.2 W of average power with near 35% slope efficiency was achieved. The thresholds for Q-switched ML, cw-ML regimes were 2.67 W and 6.13 W of pump power, respectively. For the maximum pump power of 20 W we obtained 133 nJ of pulse energy with 16-ps pulse duration, resulting in a peak power higher than 8 kW. The threshold energy density at SAM giving the QML regime was estimated to be about 30 μJ/cm², threshold of cw-ML regime was 220 μJ/cm².     

Pump-enhanced optical parametric oscillator generating continuous wave tunable terahertz radiation

We demonstrate a tunable cw terahertz (THz) parametric oscillator based on periodically poled MgO-doped lithium niobate, directly converting the 1030 nm pump wave into the THz regime. The tunability ranges from 1.2 to 2.9 THz at output power levels between 0.3 and 3.9 μW. To overcome the high pump threshold caused by THz absorption in the nonlinear crystal, we employ an enhancement cavity with a finesse of 500 at the pump wavelength. The intracavity pump threshold at 1.4 THz is measured to be 350 W for a crystal length of 2.5 cm.     

Noncascading THz-wave parametric oscillator synchronously pumped by mode-locked picosecond Ti:sapphire laser in doubly-resonant external cavity

A noncascading terahertz (THz) wave parametric oscillator synchronously pumped by a mode-locked picosecond Ti:sapphire laser whose average power was less than 1 W was demonstrated with a noncollinear phase-matching MgO:LiNbO₃ crystal in an external enhancement cavity doubly resonant for both pump (780 nm) and signal (781-784 nm) waves. In the external cavity, in which the pump wave enhanced so as to reduce the pumping threshold of parametric processes, the signal wave could also resonate and thus be enhanced simultaneously, resulting in a THz wave output at approximately 0.9 THz as the idler wave. The novel dual enhancement of pump and signal waves reduced the threshold pumping intensity to approximately 50 MW/cm², which was much lower than that of a conventional externally pumped THz wave parametric oscillator with a crystal.     

Efficient generation of orange light in a quasi-periodically poled LiTaO3 crystal

We present an approach to generating a tunable orange laser from 0.601 to 0.604 μm based on a quasi-periodically poled superlattice in LiTaO₃ and a Q-switched 1.064 μm Nd:YVO₄ laser as pump. The orange laser was generated in a cavity by a parametric process cascaded by a frequency mixing with a maximum output of 310 mW using 15 W pump power.     

6.2 W laser-diode end-pumped continuous-wave Nd:YALO3 laser at 1.34 μm

We report a compact and efficient LD end-pumped linearly polarized Nd:YAP laser operating at 1.34 μm. The laser system with different crystal lengths, output couplers and cavity types were compared. Based on optimizing of the pump system and laser cavity, 6.2 W laser radiation at 1341.4 nm with c-axis polarized was achieved, corresponding to an optical conversion efficiency of about 24.8% with respect to the incident pump power. The laser threshold was only about 1.3 W and the optical slope efficiency was up to 27.2%.     

High-power mid-infrared tunable optical parametric oscillator based on 3-mm-thick PPMgCLN

The experimental results of a high-power tunable mid-IR laser are presented. The optical parametric oscillator (OPO) with a 3-mm-thick PPMgCLN crystal was pumped by a 1.064 μm pulse laser. When the pump power of the 1.064 μm laser was 151 W at 10 kHz, and the operating temperature of the PPMgCLN with 5% MgO doping was 100°C, average output power of 23.7 W at 3.91 μm was obtained with a slope efficiency of 18.2% for the idler resonant OPO. The variation of the 3.91 μm output power was about ±4% in 10 min continuous operation. The beam quality factor M ² was less than 2.6. The average output power of 27.4 W at 3.91 μm was also obtained with 151 W pump power and the slope efficiency of 20.9% for the signal resonant OPO by changing the coating parameters of the OPO cavity mirrors. The mid-IR wavelength tunability of 3.7–4.0 μm can be achieved by adjusting the temperature of a 29 μm period PPMgCLN crystal from 200 to 30°C.     

High-power eye-safe KTA-OPO driven by YVO4/Nd:YVO4 composite laser

We present a high-power 1.53 μm laser based on intracavity KTA-OPO driven by diode-end-pumped acousto-optical Q-switched YVO₄/Nd:YVO₄ composite. The composite crystal was utilized for reducing the thermal effect, and the mode mismatch compensating OPO cavity was designed for efficient OPO conversion. The output power of eye-safe laser at 1535 nm was up to 4.4 W with the pump power of 27 W, corresponding to a diode-to-signal conversion efficiency of 16.3%. To our knowledge, this is the highest output power in diode-end-pumped circumstances. In the experiment, the strong yellow light generated by Raman conversion and frequency doubling in the KTA crystal was observed.     

Compact, single-frequency, doubly resonant optical parametric oscillator pumped in an achromatic phase-adapted double-pass geometry

We report on a nested-cavity, doubly resonant optical parametric oscillator (NesCOPO) architecture for widely tunable, mid-IR, single-frequency generation. By use of an achromatic phase-adapted double-pass pumping scheme, this new, low-threshold, semimonolithic architecture only requires two free-standing cavity mirrors and a nonlinear crystal with a mirror coating deposited on its input facet while the other facet is antireflection coated. It is thus as simple and compact as any basic linear optical parametric oscillator cavity, is easily tunable, and displays low sensitivity to mechanical vibrations. Using a high-repetition-rate (4.8?kHz) microlaser as the pump source of the NesCOPO, we demonstrate a compact source that provides pulsed, stable single-frequency output over a wide spectral range (3.8-4.3?μm) with a high peak power (up to 50?W), which are properties well suited for practical gas sensing applications.     

Continuous-tunable 4.144-4.851 μm twin-MgO:PPLN cascaded optical parametric generator pumped by a 1.342 μm Nd:GdVO4 laser

An all-solid-state mid-infrared optical parametric generator with wide tunability by using multi-grating periodically poled 5 mol.-% MgO-doped lithium niobate (MgO:PPLN) is reported. The pump source is a diode-pumped Q-switched Nd:GdVO₄ laser operated at 1.342 μm with pulse width of 150 ns and repetition rate of 50 kHz. To extend the interaction length, two identical multi-grating MgO:PPLN crystals have been cascaded in the OPG system. When the incident pump average power is 10 W, the obtained maximum idler output power is 340 mW at 4.144 μm. Compared with only using one multi-grating MgO:PPLN crystal, the obtained idler output power increases by 20.1%. 4.144-4.851 μm continuous-tunable idler output is obtained with six grating periods from 29 to 31.5 μm and temperature from 40 to 200 °C. To our knowledge, this is the first time to use 1.342 μm laser as the pump source of OPG.