Fiber-laser-based green-pumped continuous-wave singly-resonant optical parametric oscillator

Stable, high-power, second-harmonic-generation (SHG) of a compact CW Ytterbium (Yb) fiber laser at 1064 nm into the green and its use as a pump source for CW singly-resonant optical parametric oscillator (SRO) is demonstrated. Using a simple single-pass SHG configuration in MgO:sPPLT, as much as 9.6 W of single-frequency green radiation at 532 nm is generated from 30 W of fundamental power at a conversion efficiency of 32.7% in a Gaussian spatial profile with a beam quality factor of M ² < 1.3. Thermal effects have been investigated at different fundamental power levels and various thermal management schemes are employed to maximize the second-harmonic power. The green source is successfully deployed to pump a CW SRO tunable over 855–1408 nm, generating up to 2.1 W of idler at 1168 nm. The peak-to-peak idler power stability is better than 10.7% over 40 min, with beam quality factor M ² < 1.26 for the idler and M ² < 1.52 for the signal.     

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.     

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.     

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.     

High-power, continuous-wave Ti:sapphire laser pumped by fiber-laser green source at 532 nm

We report the first experimental demonstration of efficient and high-power operation of a Ti:sapphire laser pumped by a simple, compact, continuous-wave (cw) fiber-laser-based green source. The pump radiation is obtained by direct single-pass second-harmonic-generation (SHG) of a 33 W, cw Yb-fiber laser in a 30-mm-long MgO:sPPLT crystal, providing 11 W of single-frequency green power at 532 nm in TEM₀₀ spatial profile with power and frequency stability better than 3.3% and 32 MHz, respectively, over 1 h. The Ti:sapphire laser is continuously tunable across 743-970 nm and can deliver an output power up to 2.7 W with a slope efficiency as high as 32.8% under optimum output coupling of 20%. The laser output has a TEM₀₀ spatial profile with M²<1.44 across the tuning range and exhibits a peak-to-peak power fluctuation below 5.1% over 1 h.     

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).     

High power,continuous wave,singly resonant OPO based on MgO:PPLN

A continuous wave (CW), extra-cavity singly resonant optical parametric oscillator (SRO) has been demonstrated. The SRO was based on 5% Magnesium-Oxide doped periodically-poled Lithium Nio-bate (MgO:PPLN) pumped by a Yb fiber laser centered at 1064.7 nm. The SRO was able to generate light with idler wavelengths ranging from 2.9 to 4.1 μm. For a pump power of 15 W, the idler output power varied from 7.54 W at 3.03 μm to 1.04 W at 4.05 μm. The oscillation thresholds were 2.0 W at idler wavelength 3.03 μm and 7.0 W at 4.05 μm.     

High-power,high-quality ZGP OPO pumped by a Tm,Ho:GdVO<Subscript>4</Subscript> laser

We report a ZGP OPO system capable of producing >6 W at a signal wavelength of 3.80 μm and an idler wavelength of 4.45 μm. The pumping source is the Tm,Ho:GdVO₄ laser operated at 2.049 μm with an M ² of 1.07. The ZGP OPO generated a total combined output power of 6.1 W at signal wavelength and idler wavelength under pumping power of 18.3 W, and an M ² of 1.7 for OPO output was obtained.     

Gaussian- versus flat-top-pumping of a mid-IR ZGP RISTRA OPO

The influence of the pump intensity profile on the performance of a mid-IR ZGP RISTRA OPO at 6.45???m is studied for a flat-top pump profile and compared to a Gaussian pump distribution at the same pump peak fluence of 0.81?J/cm². Due to a coherent beam transformation a flat-top pump beam with a plane wavefront and excellent beam quality of M ²??1.25 is generated. The output of up to 5?mJ pulse idler energy (0.5?W average idler power) is identical in both cases, showing that flat-top pumping allows a reduction of the OPO crystal volume by 55?% while still maintaining a good output beam quality of M ²<2.7 for the idler and M ²<2.5 for the signal. The experimental results are compared to the SNLO RISTRA model and the limitations of the model are discussed.     

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.     

High efficiency KTiOAsO4 optical parametric oscillator within a diode-side-pumped two-rod Nd:YAG laser

A high efficiency KTiOAsO₄(KTA) intracavity optical parametric oscillator (IOPO) is demonstrated within a diode-side-pumped acousto-optically (AO) Q-switched two-rod Nd:YAG laser. With a 25-mm-long X-cut KTA crystal, efficient parametric conversions to signal (1.54 μm) and idler (3.47 μm) waves are realized. The highest output power of 15.8 W including 12.7 W signal and 3.1 W idler power is obtained at a repetition rate of 7.5 kHz and a pump power of 208 W, corresponding to an optical-to-optical conversion efficiency of up to 7.6%. The signal pulse duration is 32 ns with a peak power of 53 kW. At a repetition rate of 12.5 kHz and the pump power of 208 W, the highest idler power of 3.4 W is obtained with a peak power of 14 kW and a pulse duration of 19 ns. And the beam quality factors (M ²) of the signal and idler waves are determined to be around 2 and 20, respectively.     

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.     

Intra-cavity power effects in singly resonant cw OPOs

A continuous wave singly resonant optical parametric oscillator (cw SRO) has been developed that can be pumped at a level of up to 15 times its oscillation threshold by a single frequency fiber laser pump source. We report the observation of extremely high intra-cavity circulating powers of over 1 kW at the signal wavelength, and associated effects including heating of the nonlinear crystal, and beam quality degradation. Furthermore we show that these effects may be mitigated by implementing output coupling, while also extracting multi-Watt single frequency power output at both signal and idler wavelengths. PACS 42.65.Yj; 42.55.Wd; 42.62.Fi     

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.     

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.     

LD端面抽运Nd:YAG 1319/1338nm双波长激光器研究

从LD端面抽运固体激光器的激光阈值公式出发,建立了双波长激光同时振荡的阈值条件,理论计算了腔镜对于两个波长的透过率关系,实现了LD端面抽运Nd:YAG 1319nm/1338nm双波长激光连续和准连续输出.双波长激光连续输出功率可达6W,斜效率为30%;准连续输出功率在重复频率50kHz时可达4.75W,斜效率为24.73%,脉冲宽度为55.05ns;腔内插入布儒斯特片,在重复频率为50kHz时,双波长激光准连续线偏振输出功率可达2.22W,不稳定性小于0.52%,M² 关键词： 端泵Nd:YAG激光器 1319nm/1338nm双波长 声光调Q 太赫兹波     

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.     

LD端面抽运Nd:YAG 1319nm/1338nm双波长激光器研究

从LD端面抽运固体激光器的激光阈值公式出发，建立了双波长激光同时振荡的阈值条件，理论计算了腔镜对于两个波长的透过率关系，实现了LD端面抽运Nd:YAG 1319nm/1338nm双波长激光连续和准连续输出.双波长激光连续输出功率可达6W，斜效率为30%；准连续输出功率在重复频率50kHz时可达4.75W，斜效率为24.73%，脉冲宽度为55.05ns；腔内插入布儒斯特片，在重复频率为50kHz时，双波长激光准连续线偏振输出功率可达2.22W，不稳定性小于0.52%，M²     

High efficiency single- and dual-wavelength Nd : GdVO<Subscript>4</Subscript> lasers pumped by a fiber-coupled diode

Diode-end-pumped high-efficiency single- and dual-wavelength Nd:GdVO₄ lasers have been demonstrated. For the single-wavelength operation, the maximum cw output powers of 15.6 W (M²=1.54) at 1063 nm and 7.5 W (M²=1.40) at 1342 nm were achieved under the highest available pump power of 26.5 W, having the respective optical-to-optical conversion efficiencies of 59.2% and 28.2% as well as the average slope efficiencies of 65.1% and 32.2%. For the dual-wavelength operation, under the available pump power of 12.6 W, we obtained the average power outputs of 1.0 W (M²=4.85) at 1063 nm and 1.4 W (M²=3.22) at 1342 nm with the respective pulse durations of 23 ns and 53 ns for quasi-cw operation, and the power outputs of 1.8 W (M²=5.35) at 1063 nm and 2.0 W (M²=4.76) at 1342 nm for cw operation. PACS 42.65.Ky; 42.79.Nv; 42.70.Mp     

Efficient injection-seeded kHz picosecond LBO optical parametric generator

We report a highly efficient optical parametric generator (OPG) in lithium triborate (LBO). A frequency-doubled passively mode-locked diode-pumped Nd:YVO₄ oscillator amplifier (MOPA) system is used as the pump radiation source. Focussing according to the theory of Boyd and Kleinman leads to a pump power density of 50 GW/cm², which is well below the damage threshold of LBO of 80 GW/cm². The overall conversion efficiency reaches a value of 72% measured at degeneracy. The tuning range of the OPG ranges from 760 nm (signal) to 1770 nm (idler) when referring to an overall conversion efficiency of 50%. The beam quality is excellent for conversion efficiencies below 40% (M ²<1.3). The typically 10 nm (RMS) broad spectrum can be narrowed by injection seeding the OPG. Injection seeding is demonstrated for a signal wavelength of 922.54 nm. A seed cw power of 30 nW is sufficient to reduce the spectral width to 0.1 nm (RMS). The measured injection-seeded OPG pulse duration is 9 ps (FWHM). This results in a time–bandwidth product of 1.30, which is 4.1 times the theoretical limit of 0.315 for sech²-shaped pulses.