mid-IR Difference-frequency Generation Research Articles

50-µJ level, 20-picosecond, narrowband difference-frequency generation at 4.6, 5.4, 7.5, 9.2, and 10.8 µm in LiGaS2 and LiGaSe2 at Nd:YAG laser pumping and various crystalline Raman laser seedings

A comparative study of picosecond mid-IR difference frequency generation in a wide wavelength range of 4.6-10.8 µm in a simple down-converter based on the 8-mm long, high-damage-threshold crystals of LiGaS2 or LiGaSe2 under the 5-mJ, 20-ps, 1.064-µm Nd:YAG laser pumping and the single-pass crystalline (CaCO3, BaWO4, CVD-diamond) Raman laser seeding was presented. 10-µJ-level, narrowband (<2 cm−1) generation at discrete wavelengths of 4.6, 5.4, 7.5, and 9.2 µm with the optical frequencies equal to the vibrational Raman frequency or its second harmonic of various crystalline Raman seeders was demonstrated. Optimization of the pump spot and mode-matching between the pump and signal spots allowed to increase the output pulse energy up to 50 µJ in the case of LiGaSe2.

Broadband mid-IR difference-frequency generation in 5 mol % MgO-doped periodically and aperiodically poled lithium niobate

We have theoretically investigated broadband mid-infrared (mid-IR) difference-frequency generation (DFG) in 5 mol % MgO-doped periodically poled lithium niobate (5 mol % MgO : PPLN) based on quasi-phase-matching (QPM) with group-velocity matching (GVM) between the pump and the idler for the eee interaction of QPM. The acceptance bandwidths are 282.3 nm and 35.4 nm around 3.4 μm with the signal and pump wavelengths fixed at 1.550 μm and 1.064 μm, and the required QPM periods are 30.26 μm and 30.25 μm, respectively. A method which can broaden the flattop QPM DFG acceptance bandwidth (ABW) around the GVM wavelength for the idler wavelength in 5 mol % MgO-doped aperiodically poled lithium niobate (5 mol % MgO : APPLN) is proposed. The structure of 5 mol % MgO : APPLN is optimised using a genetic algorithm by adjusting its parameters. The simulation results show that under the GVM conditions, the maximum ABW for the idler is 1045.9 nm and 96.6 nm at a fixed signal wavelength of 1.550 μm and at a fixed pump wavelength of 1.064 μm, respectively. The tradeoff between the reduced effective nonlinear coefficient and DFG ABW is discussed.

Optical parametric oscillator pumped at ~1 µm with intracavity mid-IR difference-frequency generation in OPGaAs

Intracavity difference-frequency generation (DFG) between signal and idler pulses is investigated in orientation-patterned GaAs inside the cavity of a ~1 µm pumped nanosecond optical parametric oscillator (OPO). Using two different samples and temperature tuning in the non-critical configuration, tunability between 7 and 9.2 µm is demonstrated. The superior thermo-mechanical properties of OPGaAs enabled also for the first time operation of this cascaded scheme at kilohertz (1-3 kHz) repetition rates reaching average powers ~10 mW in the mid-IR.

Femtosecond mid-IR difference-frequency generation in HgGa_2S_4 from an 80 MHz optical parametric oscillator pumped at 800 nm

We employ HgGa2S4 for difference-frequency generation between signal and idler of a synchronously pumped femtosecond optical parametric oscillator at a repetition rate of 80 MHz achieving continuous tuning from ∼4 μm (33 mW) to ∼12 μm (>0.5 mW) and pulse durations of ∼220 fs.

High-power femtosecond mid-IR sources for s-SNOM applications

We demonstrate two high-power femtosecond mid-infrared (mid-IR) sources that can be combined with a scattering-type scanning near-field optical microscope (s-SNOM). The first one is based on difference frequency generation (DFG) between the two signal wavelengths of a high-power dual-signal-wavelength periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) and covers the spectral range from 10.5 μm to 16.5 μm. The second one is an AgGaSe2 OPO pumped by the PPLN OPO. With this mid-IR OPO we obtained up to 113 mW average idler power at 4857 nm with more than 40 cm−1 FWHM spectral width. We demonstrate mid-IR near-field spectra and near-field images that we obtained by combining the broadband femtosecond mid-IR DFG source with an s-SNOM.

Design of efficient single-stage chirped pulse difference frequency generation at 7 μm, driven by a dual wavelength Ti:sapphire laser

We present a design for a high-energy single stage mid-IR difference frequency generation adapted to a two-color Ti:sapphire amplifier system. The optimized mixing process is based on chirped pulse difference frequency generation (CP-DFG), allowing for a higher conversion efficiency, larger bandwidth and reduced two photon absorption losses. The numerical start-to-end simulations include stretching, chirped pulse difference frequency generation and pulse compression. Realistic design parameters for commercially available non linear crystals (GaSe, AgGaS2, LiInSe2, LiGaSe2) are considered. Compared to conventional un-chirped DFG directly pumped by Ti:sapphire technology we report a threefold increase of the quantum efficiency. Our CP-DFG scheme provides up to 340 {\mu}J pulse energy directly at 7.2 {\mu}m when pumped with 3 mJ and supports a bandwidth of up to 350 nm. The resulting 240 fs mid-IR pulses are inherently phase stable.

Mid-IR dual-wavelength difference frequency generation in uniform grating PPLN using index dispersion control

A novel widely tunable dual-wavelength mid-IR difference frequency generation (DFG) scheme with uniform grating periodically poled lithium niobate (PPLN) is presented in this paper. By using the temperature-dependent dispersion property of PPLN, the quasi-phase matching (QPM) peak for the pump may evolve into two separate ones and the wavelength spacing between them increases with the decrease of the crystal temperature. Such two pump QPM peaks may allow simultaneous dual-wavelength mid-IR laser radiations while properly setting the two fundamental pump wavelengths. With this scheme, mid-IR dual-wavelength laser radiations at around 3.228 and 3.548, 3.114 and 3.661, and 3.019 and 3.76 μm, are experimentally achieved for the crystal temperatures of 90, 65, and 30 °C, respectively, based on the fiber laser fundamental lights.

Compact and Tunable Mid-IR Light Source Based on a Dual-Wavelength Fiber Laser

A compact, tunable mid-IR difference-frequency generation (DFG) light source based on a dual-wavelength fiber laser and a 5mol% MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal is developed and evaluated. An output power of 233 μW is achieved with a conversion efficiency of 0.1%/W. The mid-IR wavelength can be tuned between 3308 nm and 3314 nm by changing the temperature of a pair of fiber Bragg grating (FBG) taking as cavity mirrors in the dual-wavelength fiber laser from 26.5°C to 106.5°C.

Femtosecond mid-IR difference-frequency generation in LiInSe_2

We employ LiInSe2 nonlinear crystal for difference-frequency generation between signal and idler of a synchronously pumped femtosecond optical parametric oscillator at 80 MHz achieving continuous tuning from 4 µm (16.7 mW) to 11.5 µm (2.3 mW).

Widely tunable mid-IR difference-frequency generation based on fiber lasers

A wide tuning technique for mid-IR difference-frequency generation (DFG) with uniform grating periodically poled LiNbO(3) (PPLN) is presented. Based on the dispersion property of the PPLN, the quasi-phase matching (QPM) band for the pump can evolve to two separate bands, and the spacing between them can be increased with the decrease of the crystal temperature. Two such separate QPM bands can be used for increasing the idler tuning range when the crystal temperature is set to adapt the pump tuning. With the technique, an idler tuning range of 690nm is experimentally achieved with fiber laser fundamental lights.

光纤型宽带可调连续波差频产生中红外激光器转换效率的研究

光纤型宽带可调连续波差频产生中红外激光器转换效率的研究

Trace gas monitor based on difference frequency generation at 4�?m using mass-production laser diodes as pump and signal light sources

New pump and signal laser sources for difference frequency generation (DFG) at 4 μm are described. A laser diode with a 980 nm fiber Bragg grating and a 785 nm Fabry-Perot (FP) laser diode were coupled into an optical fiber and mixed in a periodically poled Mg-doped lithium niobate (PPMgLN ) crystal, resulting in efficient mid-IR DFG. The DFG power was measured to be 0.23 μW for a pump power of 5 mW and a signal power of 50 mW with a slope efficiency of 0.92 mW/W2. A Doppler-broadened absorption spectrum of N2O at 2485.2 cm-1 (3.927 μm) was observed in a 0.1 m-long gas cell at a pressure of 133 Pa. The spectral linewidth of the DFG source was estimated to be 161 MHz (FWHM) for an averaging time of 700 ms. Real-time monitoring of N2O in a multipass cell with an optical path length of 36 m at a concentration level of 1 ppm was demonstrated.

Trace-gas sensor based on mid-IR difference-frequency generation in PPLN with saturated output power

The development and characterization of a compact pulsed mid-IR laser source for sensitive on-line trace-gas analyses in the 3–4 μm wavelength range is reported. The source is based on an advantageous difference-frequency mixing configuration in periodically poled LiNbO 3 (PPLN) with a cw external-cavity diode laser (ECDL; 810–830 nm) for broad and accurate tunability and a diode-pumped passively Q-switched Nd:YAG laser (1064 nm) for high mid-IR peak power. With 5 mW cw pump and 4.7 kW signal peak power incident on a 19 mm long PPLN crystal, a maximum of 360 μW mid-IR peak power was generated. The narrowband (∼150 MHz) radiation was saturated by a factor of 15 compared with the nonsaturated case due to depletion of the pump laser radiation. This results in a very high amplitude stability of the generated mid-IR power and thus in a high detection sensitivity. A minimum detectable absorption coefficient of 2.8×10 −8 cm −1 was achieved in combination with a 36.2 m multipass cell in an averaging time of 20 s, as demonstrated by on-line analyses of formaldehyde traces near 3.53 μm.