Pump-enhanced difference-frequency generation at 3.3 μm
M. F. Witinski, J. B. Paul, and J. G. Anderson
Abstract
The demonstration of continuous wave intracavity difference-frequency generation in the mid-infrared (mid-IR) is presented. A cavity for pump laser enhancement is constructed around a periodically poled lithium niobate crystal, and the cavity length is locked to the frequency of the pump laser using the Pound-Drever-Hall technique, producing a gain of 12 in the resultant idler power compared to the single-pass case. A widely tunable single-mode 3.3 μm idler beam with a power of nearly 10 mW is available for direct absorption spectroscopy. The pump-enhancement method demonstrated here should be readily scalable to produce hundreds of milliwatts of mid-IR light by using higher power signal and pump lasers.
A DFG-based cavity ring-down spectrometer for trace gas sensing in the mid-infrared
K. E. Whittaker, L. Ciaffoni, G. Hancock, R. Peverall and G. A. D. Ritchie
Abstract
Continuing studies into an all-diode laser-based 3.3µm difference frequency generation cavity ring-down spectroscopy system are presented. Light from a 1,560 nm diode laser, amplified by an erbium-doped fibre amplifier, was mixed with 1,064 nm diode laser radiation in a bulk periodically poled lithium niobate crystal to generate 16µW of mid-IR light at 3,346 nm with a conversion efficiency of 0.05%W-1cm-1. This radiation was coupled into a 77 cm long linear cavity with average mirror reflectivities of 0.9996, and a measured baseline ring-down time of 6.07±0.03µs. The potential of such a spectrometer was illustrated by investigating the P(3) transition in the fundamental 3F2 band of CH4 both in a 7.5 ppmv calibrated mixture of CH4 in air and in breath samples from methane and non-methane producers under conditions where the minimum detectable absorption coefficient (αmin) was 2.8 x 10-8cm-1 over 6 s using a ring-down time acquisition rate of 20 Hz. Allan variance measurements indicated an optimum αmin of 2.9 x 10-9cm-1 over 44 s.
Combining a DS-DBR laser with QPM-DFG for mid-infrared spectroscopy
K. E. Whittaker, L. Ciaffoni, G. Hancock, M. Islam, R. Peverall and G. A. D. Ritchie
Abstract
Studies into the suitability of a novel, widely tunable telecom L-band (1563–1613 nm) digital supermode distributed Bragg reflector (DS-DBR) laser for spectroscopy in the mid-IR are presented. Light from the DS-DBR laser was mixed with 1064 nm radiation in a periodically poled lithium niobate (PPLN) crystal to generate mid-IR light by quasi phase matching difference frequency generation (QPM-DFG). The resultant continuous wave radiation covered the range 3000–3200 cm−1 with powers of up to 2.6 μW. The use of such laser light for spectroscopic applications was illustrated by performing absorption experiments on both narrow-band and broad-band absorbers, namely methane (CH4) and methanethiol (CH3SH). Wavelength modulation spectroscopy (WMS) on CH4 demonstrated that the modulation characteristics of the DS-DBR laser observed in the near-IR were transposed to the mid-IR and yielded a sensitivity of 3.1×10−6 cm−1Hz−1/2 over a 47 cm path length. In the CH3SH spectrum, the absorption feature at 3040 cm−1 was identified as a potential useful region for monitoring this biomarker in exhaled breath at reduced pressures.
DFG-based mid-IR generation using a compact dual-wavelength all-fiber amplifier for laser spectroscopy applications
K. Krzempek, G. Sobon, and K. M. Abramski
Abstract
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 (CH4) in ambient air with estimated minimum detectable concentration at a level of 26 ppbv.
Mid-infrared multi-mode absorption spectroscopy, MUMAS, using difference frequency generation
H. Northern, S. O’Hagan, M. L. Hamilton, and P. Ewart
Abstract
Multi-mode absorption spectroscopy of ammonia and methane at 3.3 μm has been demonstrated using a source of multi-mode mid-infrared radiation based on difference frequency generation. Multi-mode radiation at 1.56 μm from a diode-pumped Er:Yb:glass laser was mixed with a single-mode Nd:YAG laser at 1.06 μm in a periodically poled lithium niobate crystal to produce multi-mode radiation in the region of 3.3 μm. Detection, by direct multi-mode absorption, of NH3 and CH4 is reported for each species individually and also simultaneously in mixtures allowing measurements of partial pressures of each species.
Mid-infrared optical frequency combs based on difference frequency generation for molecular spectroscopy
Flavio C. Cruz, Daniel L. Maser, Todd Johnson, Gabriel Ycas, Andrew Klose, Fabrizio R. Giorgetta, Ian Coddington, and Scott A. Diddams
Abstract
Mid-infrared femtosecond optical frequency combs were produced by difference frequency generation of the spectral components of a near-infrared comb in a 3-mm-long MgO:PPLN crystal. We observe strong pump depletion and 9.3 dB parametric gain in the 1.5 μm signal, which yields powers above 500 mW (3 μW/mode) in the idler with spectra covering 2.8 μm to 3.5 μm. Potential for broadband, high-resolution molecular spectroscopy is demonstrated by absorption spectra and interferograms obtained by heterodyning two combs.
Fully-integrated dual-wavelength all-fiber source for mode-locked square-shaped mid-IR pulse generation via DFG in PPLN
Karol Krzempek, Grzegorz Sobon, Jaroslaw Sotor, and Krzysztof M. Abramski
Abstract
First demonstration of a dissipative soliton resonance (DSR), double-clad (DC) active fiber, mode-locked figure-8 laser (F8L) enabling simultaneous amplification of 1064 nm seed signal is presented. Appropriate design supported peak power clamping (PPC) effect in the laser resonator and enabled easy tuning of the generated, square-shaped pulses from 20 ns to 170 ns. By incorporating a circulator-based isolating element in the directional loop of the laser, record pulse energy of 2.13 μJ was achieved, directly at the output of the resonator. The usability of the unique dual-wavelength design was experimentally put to a test in a difference frequency generation (DFG) setup using periodically poled lithium niobate (PPLN) crystal.
Mid-Infrared Difference Frequency-Generation with Synchronized Fiber Lasers
R. T. Murray, T. H. Runcorn, E. J. R. Kelleher, S. Guha, and J. R. Taylor
Abstract
We present results on high-average power difference frequency generation of pulsed Yb/Er fiber systems to the mid-IR (6.2 W at 3.35 μm), and use focused Gaussian beam theory to validate our experimental results.
Mid-infrared dual-comb spectroscopy with electro-optic modulators
M. Yan, P. Luo, K. Iwakuni, G. Millot, and T. Hänsch
Abstract
We demonstrate dual-comb spectroscopy based on difference frequency generation of frequency-agile near-infrared frequency combs, produced with the help of electro-optic modulators. The combs have a remarkably flat intensity distribution and their positions and line spacings can be selected freely by simply dialing a knob. We record, in the 3-micron region, Doppler-limited absorption spectra with resolved comb lines within milliseconds. Precise molecular line parameters are retrieved. Our technique holds promise for fast and sensitive time-resolved studies e.g. of trace gases.
Multi-Watt-level 3.28-3.45 um difference frequency generation using synchronous fiber lasers
R.T. Murray, E. J. R. Kelleher, T. Runcorn, and J. R. Taylor
Abstract
We report multi-Watt-level average power 3.28-3.45 μm difference frequency generation using two sychronous picosecond master oscillator power fiber amplifiers. Greater than 3.4 W of idler power is generated across the entire spectral tuning range.
