Dual-wavelength Oscillator Research Articles

Fiber-laser-pumped, dual-wavelength, picosecond optical parametric oscillator.

We report a simple, compact, picosecond, dual-wavelength optical parametric oscillator (DW-OPO) at 160 MHz, based on two MgO:PPLN crystals sharing the same cavity and synchronously pumped by an Yb-fiber laser at 1064 nm. The two signal and idler wavelength pairs are independently tunable in the near- and mid-infrared across 1550-1615 nm and 3118-3393 nm, respectively, and can be arbitrarily tuned, even to degeneracy and beyond, without coherent coupling, irrespective of operating wavelength. The DW-OPO provides two signal and idler pulse trains and delivers as much as 1.5 W of average signal power at a degenerate wavelength of 1550 nm from each arm, at a total (signal plus idler) power extraction efficiency of as much as 44%. The two output signal pulse trains have durations of ∼18 ps and ∼15.2 ps, with Gaussian spatial quality, and exhibit passive power stability, better than 3.6% rms over >5 h. We also demonstrate the possibility of tailoring the pulse trains from the DW-OPO by controlling the delay between the pump pulses at the input to the two MgO:PPLN crystals.

Evaluation of polarized terahertz waves generated by Cherenkov phase matching

We report terahertz (THz) wave generation by satisfying Cherenkov phase-matching condition in both s and p polarizations. A dual-wavelength optical parametric oscillator is constructed from two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. By rotating the orientation of both a lithium niobate crystal (LiNbO3) and the polarization of the pump waves, the polarization of the THz wave changes. Due to the difference in the refractive index and absorption, the output power for p polarization is one tenth that for s polarization. A tuning range from 0.2 to 6.5 THz is obtained for s polarization, and from 0.2 to 4.2 and 5.4 to 6.9 THz for p polarization. The extraction efficiency is improved by changing the angle of prism for p polarization, and a large phase change occurs at total internal reflection. Consequently, p-polarized THz waves are optimal for spectroscopic applications.

Broadband THz-wave generation by satisfying the noncollinear phase-matching condition with a reflected signal beam

We demonstrated broadband terahertz (THz) wave generation by satisfying the noncollinear phase-matching condition with a reflected signal beam. We constructed a dual-wavelength optical parametric oscillator with two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. The collinear pump and signal waves were irradiated into a lithium niobate crystal. The pump and the signal waves were reflected at the crystal surface. Because the pump and the signal waves have a finite beam diameter, when the reflected signal wave and unreflected pump wave were irradiated at the correct angle, the noncollinear phase-matching condition was satisfied. By changing the incident angle to the crystal, broadband THz-wave generation with a range of over 0.2-7.2THz was achieved.

A fiber laser pumped dual-wavelength mid-infrared optical parametric oscillator based on aperiodically poled magnesium oxide doped lithium niobate

We report a fiber laser pumped dual-wavelength mid-infrared optical parameter oscillator (OPO) based on an aperiodic optical superlattice (AOS) structure. An aperiodically poled MgO-doped lithium niobate wafer was designed and fabricated as the nonlinear crystal for the OPO. Using a linearly polarized pulsed Yb fiber laser at 1.064 μm as the pump source, mid-infrared emissions at 3.3 and 3.8 μm were obtained simultaneously from the OPO. The total output power at the idler wavelengths of 3.3 and 3.8 μm reached 3.07 W under the maximum pump power of 27 W. The pump-to-idler conversion efficiency was 11.4% with a ratio of about 1.2:1 for 3.3 μm and 3.8 μm.

DFG-based mid-IR generation using a compact dual-wavelength all-fiber amplifier for laser spectroscopy applications

We demonstrate a compact mid-infrared (mid-IR) radiation source based on difference frequency generation (DFG) in periodically poled lithium niobate (PPLN) crystal. The system incorporates a dual-wavelength master oscillator power amplifier (MOPA) source capable of simultaneous amplification of 1064 nm and 1548 nm signals in a common active fiber co-doped with erbium and ytterbium ions. Two low-power seed lasers were amplified by a factor of 14.4 dB and 23.7 dB for 1064 nm and 1548 nm, respectively and used in a nonlinear DFG setup to generate 1.14 mW of radiation centered at 3.4 μm. The system allowed for open-path detection of methane (CH(4)) in ambient air with estimated minimum detectable concentration at a level of 26 ppbv.

Development of an ultra-widely tunable DFG-THz source with switching between organic nonlinear crystals pumped with a dual-wavelength BBO optical parametric oscillator

We developed a difference frequency generation (DFG) source with an organic nonlinear optical crystal of DAST or BNA selectively excited by a dual-wavelength β-BaB(2)O(4) optical parametric oscillator (BBO-OPO). The dual-wavelength BBO-OPO can independently oscillate two lights with different wavelengths from 800 to 1800 nm in a cavity. THz-wave generation by using each organic crystal covers ultrawide range from 1 to 30 THz with inherent intensity dips by crystal absorption modes. The reduced outputs can be improved by switching over the crystals with adequately tuned pump wavelengths of the BBO-OPO.

Compact and tunable mid-infrared source based on a 2 μm dual-wavelength KTiOPO4 intracavity optical parametric oscillator

Using a double resonant KTiOPO4 (KTP) intracavity optical parametric oscillator operating at degenerated point of 2 μm, we demonstrate a unique mid-infrared source based on difference frequency generation in GaSe crystal. The output tuning range is 8.42–19.52 μm, and a peak power of 834 W for type-I phase matching scheme and 730 W for type-II phase matching scheme are achieved. Experimental results show that this oscillator is a good alternative to the generator of a compact and tabletop mid-infrared radiation with a widely tunable range.

High energy dual-wavelength mid-infrared extracavity KTA optical parametric oscillator

A high energy dual-wavelength extracavity KTA optical parametric oscillator (OPO) with excellent stability and beam quality, which is pumped by a Q-switched single-longitudinal-mode Nd:YAG laser, has been demonstrated based on a type II noncritical phase matching (NCPM) KTA crystal. The maximum pulse energy of 10 mJ with the output stability of better than 4.5% rms at 3.467 μm is obtained at the repetition rate of 10 Hz and pulse width of 2 ns, and the 11.7 mJ of 1.535 μm radiation is obtained simultaneously. This extracavity NCPM KTA OPO is very useful when high energy, high beam quality and smooth time domain are needed.

Dual-wavelength single-crystal double-pass KTP optical parametric oscillator and its application in terahertz wave generation

A tunable dual-wavelength double-pass singly resonant optical parametric oscillator based on a single KTP crystal has been proposed and demonstrated. By setting the rear mirror tuning angle precisely, collinear and noncollinear dual phase matching can be established simultaneously and leads to a two-wavelength oscillation at steady state. With high-speed KTP angle tuning, two wavelengths and their frequency difference can be adjusted continuously and accurately. By using this newly developed dual-wavelength optical parametric oscillator to pump a DAST crystal, a monochromatic terahertz wave ranging from 0.5 to 3 THz has been successfully generated in a difference-frequency generation system.

Tunable and coherent nanosecond 7.2–12.2 μm mid-infrared generation based on difference frequency mixing in ZnGeP2 crystal

A coherent mid-infrared laser source, which can be tuned from 7.2 μm to 12.2 μm based on the type-II phase-matched difference frequency generation (DFG) in an uncoated ZnGeP2 (ZGP) crystal, is reported. The two pump waves are from a type-II phase-matched dual-wavelength KTP optical parametric oscillator (OPO) of which the signal and idler waves are tuned during 1.85–1.96 μm (extraordinary wave) and 2.5–2.33 μm (ordinary wave), respectively. The maximum energy of the generated mid-infrared laser is 10 μJ at 9.22 μm, corresponding to the peak power of 2.2 kW.

Random Frequency Accessible Broad Tunable Terahertz-Wave Source Using Phase-Matched 4-Dimethylamino-N-methyl-4-stilbazolium Tosylate Crystal

Random frequency accessible, ultra-broad-band (1.5–37 THz) THz-wave generation was demonstrated using difference frequency generation (DFG) in an organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal. Such DAST crystals are promising materials for efficient and high-power THz-wave generation because of their very high nonlinearity and low refractive index dispersion between the near-infrared region and the THz-wave region. We can use the highest nonlinear component of DAST, d11 (about 230 pm/V), to generate THz waves using DFG because the collinear phase-matching condition of the Type 0 configuration is satisfied. We constructed a dual-wavelength optical parametric oscillator (OPO) with two KTP crystals pumped by a frequency-doubled Nd:YAG laser. Each KTP crystal was set on a galvano scanner. The angle of each crystal was controlled independently. The OPO is tunable at 1300–1900 nm, giving an ultra-broad tunable range of the THz wave. We generated an ultra-broad tunable THz wave using only one DAST crystal without any change of the experimental setup aside from the computer-controlled galvano-scanner angle change. The highest THz-wave energy of 10 nJ was obtained at around the 26 THz region under 2 mJ of pumping energy. Also, the THz-wave source can access a desired THz frequency at every pulse (50 Hz at present). The galvano scanner has 1 kHz of response, with 1-ms frequency access speed.

High-power terahertz-wave generation using DAST crystal and detection using mid-infrared powermeter

The exact power output of a table-top-sized terahertz (THz)-wave source using a nonlinear optical process has not been clarified because detectors for these experiments [Si bolometer, deuterated triglycine sulfate (DTGS), etc.] are not calibrated well. On the other hand, powermeters for the mid-infrared (mid-IR) region are well established and calibrated. We constructed a high-power dual-wavelength optical parametric oscillator with two KTP crystals as a light source for difference frequency generation. The obtained powers of dual waves were 21 mJ at ~1300 nm, ten times higher than that of the previous measurement. The device provides high-power THz-wave generation with ~100 times greater output power than that reported in previous works. A well-calibrated mid-IR powermeter at ~27 THz detected the generated THz wave; its measured energy was 2.4 microJ. Although the powermeter had no sensitivity in the lower-frequency range (below 20 THz), the pulse energy at such a low-frequency region was estimated in reference to the output spectrum obtained using a DTGS detector: the energy would be from about the submicrojoule level to a few microjoules in the THz-wave region.

Collinear phase-matched terahertz-wave generation in GaP crystal using a dual-wavelength optical parametric oscillator

Tunable terahertz (THz)-wave generation in GaP crystal was theoretically and experimentally investigated using collinear difference frequency mixing. The wavelength range and length of GaP crystal for efficient difference frequency generation (DFG) were determined by calculating the phase-matching conditions. THz waves from 0.5 to 4.5 THz were generated by collinear phase-matched DFG using a dual-wavelength optical parametric oscillator with two KTiOPO4 crystals in the range of 930–1000 nm. A maximum THz output energy of 5.3 nJ/pulse (peak power of 0.66 W) at 1.9 THz was obtained when the pump energy was 1.2 mJ/pulse.

Widely tunable terahertz-wave generation in an organic crystal and its spectroscopic application

Terahertz (THz)-wave generation using difference-frequency mixing in an organic 4-N, N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystal was investigated theoretically and experimentally. We developed a dual-wavelength optical parametric oscillator (OPO) with two KTiOPO4 crystals as the input light source. This oscillator has a tunable range from 1300–1450 nm and is pumped by a diode-pumped, frequency-doubled, Q-switched Nd:YAG laser with a pulse duration of 10 ns. Widely tunable THz waves ranging from 2 to 20 THz were generated from DAST crystals with 0.5- and 1-mm thickness using the OPO. THz output energies of 82 nJ (peak power of 10.3 W) at 11.6 THz and 110 nJ (peak power of 13.8 W) at 19 THz were obtained with a 1-mm-thick DAST crystal. Using a tunable THz-wave system consisting of the THz source and a pyroelectric detector, THz spectroscopic data for a polytetrafluoroethylene sheet were obtained and were comparable to data obtained from a conventional far-infrared spectrometer.

Regeneratively modelocked dual-wavelength soliton-pulse fibre-optical parametric oscillator in C- and L-bands

A self-starting regeneratively modelocked fibre-optical parametric oscillator that utilises four-wave mixing in a highly nonlinear fibre together with intra-cavity soliton formation to generate tunable, dual-wavelength picosecond pulses at 10 GHz rate simultaneously in the C- and L-bands, is demonstrated, believably for the first time. An electroabsorption-modulator-based optoelectronic oscillator is used as an ultra-low-jitter pump source that enables, by means of direct feedback injection locking, a significant reduction of the timing jitter of the obtained pulses.

Continuously tunable THz and far-infrared wave generation from DAST crystal

Continuously tunable terahertz (THz) and far-infrared waves over a wide range of 2 to 30 THz were generated in a 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) crystal by difference frequency mixing. A dual-wavelength optical parametric oscillator in the range of 1250 to 1450 nm as the input light source was developed.

Mid-infrared pulses generated from the mixing output of an amplified, dual-wavelength Ti:sapphire system

We demonstrate the generation of femtosecond mid-infrared pulses by direct difference-frequency mixing in a AgGaS(2) crystal of two intense pulses from a dual-wavelength oscillator that have been simultaneously amplified in a single regenerative amplifier. A pulse energy of as much as 1.6 muJ was achieved at wavelengths of 9-11 mum.

Dual-wavelength chirped-pulse amplification system

We demonstrate a chirped-pulse amplification system that simultaneously amplifies two pulses from a dual-wavelength oscillator in a single regenerative amplifier. The two wavelengths can be tuned from 800 to 890 nm. The total energy of 1.5 mJ can be variably split between the two pulses. The pulses are 150 fs in duration and have 60-fs timing jitter.