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).     

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.     

All fiber MOPA laser-pumped,continuous-wave,mid-infrared,singly-resonant optical parametric oscillator based on periodically poled MgO-Doped LiNbO<Subscript>3</Subscript>

We report a continuous-wave (CW) mid-infrared singly resonant optical parametric oscillator (SRO) based on periodically poled MgO-doped LiNbO₃ (PPMgLN) pumped by a high power, single frequency fiber laser in master oscillator-power amplifier (MOPA) configuration at 1.064 μm. Using four-mirror ring OPO cavities, at the PPMgLN’s grating period of 30.5 μm and the temperature of 23°C, we achieved the maximum idler output power of 7.2 W at 3.4 μm when the pump power was 52.8 W. The total power-conversion efficiency from the pump to the idler in this experiment is about 13.6%, and corresponds to ∼44% of quantum-limited performance.     

Cr4+:YAG passively Q-switched c-cut Nd:YVO4 self-Raman laser at 1168.6 nm

We demonstrate the first Cr⁴⁺:YAG passively Q-switched c-cut Nd:YVO₄ self-Raman laser at 1168.6 nm based on the Stokes shift of 816 cm⁻¹. At the pump power of 4.7 W, the maximum output power of the Stokes line at 1168.6 nm is 270.5 mW, corresponding to an optical conversion efficiency of 5.8%. The pulse width, pulse repetition rate, pulse energy and peak power are 8.8 ns, 35.8 kHz, 7.6 μJ and 0.86 kW, respectively. At the pump of 5.0 W, the Stokes line at 1097.2 nm based on Raman shift of 259 cm⁻¹ also appears.     

The study on the nonlinear optical response of Sudan I

The nonlinear optical properties of Sudan I were investigated by a single beam Z-scan technique. The Sudan I ethanol solution exhibited large nonlinear refractive indices under both CW and pulse laser excitations. The nonlinear refractive indices of Sudan I were in the order of ?10^?8 cm²/W under CW 633 nm excitation and ?10^?6 cm²/W under CW 488 nm excitation, respectively. Under the excitation of a pulse 532 nm laser, the nonlinear refractive index n₂ was calculated to be 1.19 × 10^?14 cm²/W. It was discussed that the mechanism accounting for the process of nonlinear refraction was attributed to the laser heating for the CW laser excitation and the electronic effect for the pulse excitation. Moreover, the second hyperpolarizability of Sudan I was also estimated in this paper.     

High-energy PPMgLN optical parametric oscillator pumped by a 1.064 μm E-O Q-Switched Nd:YAG laser

A high-energy PPMgLN optical parametric oscillator (OPO) pumped by a E-O Q-switched Nd:YAG laser working at 1.064 μm was successfully illustrated. A maximum output pulse energy of 3.4 mJ was obtained with a pump threshold of 1.5 mJ and a slope efficiency of 30% around room temperature. The OPO output signal and idler wavelength were 1552 and 3384 nm, respectively. The damage to the input surface of PPMgLN crystal was carefully observed with a damage threshold of 4.6 J/cm².     

Terahertz emission dependence on the intensity ratio of 400–800 nm in generating terahertz waves from two-color laser-induced gas plasma

A transient photocurrent model is used to explain terahertz emission from gas plasma irradiated by a laser pulse and the second harmonic. By introducing the second harmonic, 400 nm, the corresponding terahertz emission is greatly enhanced. The exact dependence of terahertz emission on the intensity ratio of 400–800 nm is studied for the case with total intensity of 5.00 × 10¹⁴ W/cm². Results show the emission reaches the maximum at about the case for energy distribution of I_ω = 4.00 × 10¹⁴ W/cm², I_2ω = 1.00 × 10¹⁴ W/cm².     

Two photon absorption characteristics of bulk GaTe crystal

We have investigated the structural and optical properties of bulk GaTe crystal grown by vertical Bridgman method. Two photon absorption (TPA) properties of GaTe crystal have been investigated by the open aperture Z-scan technique under 1064 nm wavelength with 4 ns or 65 ps pulse durations. The TPA coefficients are greater in ns regime than that of ps regime. Upon increasing intensity of incident light from 5.02×10⁷ W/cm² to 1.07×10⁸ W/cm², the TPA coefficients increased from 3.47×10^?6 cm/W to 8.53×10^?6 cm/W for nanosecond excitation. Similarly, when intensity of incident light was increased from 6.81×10⁸ W/cm² to 9.94×10⁸ W/cm² the TPA coefficients increased from 3.53×10^?7 cm/W to 6.83×10^?7 cm/W for picosecond excitation. Measured TPA coefficient of GaTe crystal is larger than that of GaSe and GaS layered crystals.     

Diode-pumped actively Q-switched Nd:GGG laser operating at 938 nm

The stimulated emission cross-section of Nd:GGG crystal in 938 nm transition was measured by the amplifier approach. It is 2.3×10^?20 cm². A quasi-continuous-wave diode pumped, actively Q-switched Nd:GGG laser operating at 938 nm was demonstrated. Pumped by laser diodes with 900 W peak power and 300 μs pulse duration, it generated 168 mJ energy in long pulse mode. The slope efficiency was 36%. Q-switched by a KD?P Pockels cell, 41 mJ output pulse energy was obtained. The pulse duration and peak power were 120 ns and 340 kW, respectively. The optical to optical efficiency was 7%.     

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.     

Study on the spectral characteristics of the cascaded parametric conversion in a single cavity tandem multi-channel PPMgLNs-based optical parametric oscillator

We report an acousto-optic Q-switched Nd:GdVO₄ laser pumped flexibly tunable cascaded optical parametric oscillator (OPO) based on two separate multi-channel periodically poled magnesium oxide doped Lithium Niobate (PPMgLN). Even under lower pump power, long wavelength parametric output was found to be more easily generated than in single stage OPO. A cascaded idler output at 5.075 μm was found to be generated. A convenient method to monitor the occurring of the cascaded parametric process was also presented by measuring the spectrum of sum-frequency generation of the pump power and the cascaded signal power.     

High index contrast Er:Ta2O5 waveguide amplifier on oxidised silicon

We report a high index contrast erbium doped tantalum pentoxide waveguide amplifier. 2.3 cm long waveguides with erbium concentration of 2.7 × 10²⁰ cm^? 3 were fabricated by magnetron sputtering of Er-doped tantalum pentoxide on oxidised silicon substrates and Ar-ion milling with photolithographically defined mask. A net on-chip optical gain of ~ 2.25 dB/cm at 1531.5 nm was achieved with 20 mW of pump power at 977 nm launched into the waveguide. The pump threshold for transparency was 4.5 mW.     

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.     

Tunable single-longitudinal-mode operation of a sandwich-type YAG/Ho:YAG/YAG ceramic laser

We present a 2.09 μm single-longitudinal-mode sandwich-type YAG/Ho:YAG/YAG ceramic laser pumped by a Tm-doped fiber laser for the first time. A pair of F-P etalons was used to achieve tunable single-longitudinal-mode operation. The maximum single-longitudinal-mode output power of 530 mW at 2091.4 nm was obtained with an absorbed pump power of 8.06 W, corresponding to an optical conversion efficiency of 6.6% and a slope efficiency of 12.7%. Wavelength tunable was achieved by tuning the angle of etalons and the wavelength could be tuned from 2091.1 nm to 2092.1 nm, corresponding to a tuning frequency of 68 GHz. The M² factor was measured to be 1.23.     

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.     

Semiconductor type single wall carbon nanotube absorber for passive mode-locked Nd:YVO4 laser

The pure semiconductor type single wall carbon nanotubes (SWCNT) was transferred on hydrophilic glass substrate to fabricate saturable absorbers by vertical evaporation technique. The recovery time of the absorber is 350 fs. The saturation intensity of the absorber was found to be 115 μJ/cm² at 1060 nm. The modulation depth of the absorber could be about 7%. Passive mode-locked Nd:YVO₄ laser using this kind of absorber was demonstrated. The largest average output power of the mode-locked laser is 1.4 W at the pump power of 7.8 W. The continuous wave mode-locked pulses with the repetition of 80 MHz were achieved.     

High power single-longitudinal-mode Ho:YLF unidirectional ring laser based on a composite structure of acousto-optic device and wave plate

We report a unidirectional single-longitudinal-mode Ho:YLF ring laser. An acousto-optic modulator and two half-wave plates were used to enforce the Ho:YLF ring laser in a unidirectional operation. The single-longitudinal-mode output power could reach 3.73 W successfully when the incident pump power was 16.4 W. The corresponding slope efficiency was 27.1%. The wavelength of the single-longitudinal-mode Ho:YLF ring laser was 2063.8 nm. The M² factor was 1.12. The results illustrated that the single-longitudinal-mode output power could be further enhanced by increasing the radio frequency power of the acousto-optic modulator.     

An eye-safe KTiAsO4 intracavity optical parametric oscillator driven by a diode pumped composite Nd:YAG/Cr4+:YAG laser

A mini eye-safe KTiAsO₄ intracavity optical parametric oscillator (IOPO) employing the shared cavity configuration and driven by a diode-end-pumped composite Nd:YAG/Cr⁴⁺:YAG laser is demonstrated in this paper. Under an incident laser diode power of 11 W, a maximum average output power of 424 mW at 1534 nm was obtained. The corresponding signal pulse width and repetition rate were 1.2 ns and 16.7 kHz, respectively. The fluctuation of the average signal output power over long-term operation was found to be ±3.0%. A theoretical model for the compact IOPO was also presented in this paper.     

Optical temperature sensor through infrared excited blue upconversion emission in Tm3 +/Yb3 + codoped Y2O3

An analysis of the intense blue upconversion emission at 476 and 488 nm in Tm^3 +/Yb^3 + codoped Y₂O₃ under excitation power density of 86.7 W/cm² available from a diode laser emitting at 976 nm, has been undertaken. Fluorescence intensity ratio (FIR) variation of temperature-sensitive blue upconversion emission at 476 and 488 nm in this material was recorded in the temperature range from 303 to 753 K. The maximum sensitivity derived from the FIR technique of the blue upconversion emission is approximately 0.0035 K^? 1. The results imply that Tm^3 +/Yb^3 + codoped Y₂O₃ is a potential candidate for the optical temperature sensor.     

Gain properties of the transition emissions near the second telecommunication window in Ho3+-doped multicomponent heavy-metal gallate glasses

Efficient infrared emissions near the second telecommunication window in Ho³⁺-doped multicomponent heavy-metal gallate (MHG) glasses have been observed. The maximum stimulated emission cross-sections are calculated to be 2.94×10^?21 and 2.08×10^?21 cm² for 1200 and 1390 nm emissions, respectively. Excitation spectra reveal that the 642 and 538 nm wavelengths are practical pumping conditions for 1.2 and 1.39 μm emissions, respectively. Gain cross-sections are evaluated and positive gain bands have been anticipated. The theoretical gain results indicate that the appealing infrared emissions near the second telecommunication window from Ho³⁺-doped MHG glasses with low maximum phonon energy of ～660 cm^?1 make them attractive in developing ～1.2 μm and E-band (1360–1460 nm) optical amplifiers.