[Show abstract][Hide abstract] ABSTRACT: Laser ablation proved to be a reliable micro-fabrication technique for patterning and structuring of both thin film and bulk polymer materials. In most of the industrial applications ultra-violet (UV) laser sources are employed, however they have limitations such as maintenance costs and practical issues. As an alternative and promising approach, mid-infrared resonant laser ablation (RIA) has been introduced, in which the laser wavelength is tuned to one of the molecular vibrational transi-tions of the polymer to be ablated. Consequently, the technique is selective in respect of processing a diversity of polymers which usually have different infrared absorption bands. In this paper, we present mid-infrared resonant ablation of PolyMethyl MethAcrylate (PMMA), employing nanosec-ond laser pulses tunable between 3 and 4 microns. This RIA nanosecond laser set-up is based on a commercial laser at 1064 nm pumping a singly resonant Optical Parametric Oscillator (OPO) built around a Periodically-Poled Lithium Niobate (PPLN) crystal with several Quasi-Phase Matching (QPM) periods. RIA has been successfully demonstrated for structuring bulk PMMA, and selective patterning of PMMA thin films on a glass substrate has been implemented.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a robust and simple method for measurement, stabilization and tuning of the frequency of cw mid-infrared (MIR) lasers, in particular of quantum cascade lasers. The proof of principle is performed with a quantum cascade laser at 5.4 µm, which is upconverted to 1.2 µm by sum-frequency generation in orientation-patterned GaAs with the output of a standard high-power cw 1.5 µm fiber laser. Both the 1.2 µm and the 1.5 µm waves are measured by a standard Er:fiber frequency comb. Frequency measurement at the 100 kHz-level, stabilization to sub-10 kHz level, controlled frequency tuning and long-term stability are demonstrated.
[Show abstract][Hide abstract] ABSTRACT: Progress in processing low-loss quasi-phase-matched gallium arsenide crystals makes it possible to benefit from their excellent nonlinear properties in practical mid-infrared sources. This paper addresses both crystal growth aspects and the most recent device demonstrations.
[Show abstract][Hide abstract] ABSTRACT: Progress in processing low-loss quasi-phase-matched gallium arsenide crystals allows their excellent nonlinear properties to be employed in practical mid infrared devices. This presentation will address both crystal growth aspects and the most recent devices demonstrations.
[Show abstract][Hide abstract] ABSTRACT: Due to a wide transparency range (0.9-17 mum), a low absorption loss (~ 0.01 cm-1), and a laser damage threshold comparable to ZGP crystals (~ 2 J/cm2), combined with excellent nonlinear, thermal and mechanical properties, quasi-phase-matched orientation-patterned gallium arsenide (OP-GaAs) crystals are well adapted for efficient mid-infrared optical parametric oscillators (OPOs). The paper discusses the best results obtained, to our knowledge, with an OP-GaAs OPO pumped by a Qswitched 2.09 mum Ho3+:YAG laser. The compact (33 × 48 cm) high-repetition rate source developed allows to achieve 4.0 W of average output power in the 3-5 mum range at 40 kHz repetition rate with a 45 % slope efficiency and a very good beam quality (M2 < 1.8). 6.4 W were obtained at 70 kHz with a 51 % slope efficiency, and 7.7 W at 100 kHz with a 46 % slope efficiency. At 40 kHz and 70 kHz, an optical damage occurred at a fluence of 1.9 J/cm2 and 1.5 J/cm2 respectively. The power is limited by the OP-GaAs crystal thickness and is expected to be scaled in thicker samples recently fabricated.
[Show abstract][Hide abstract] ABSTRACT: Among quasi-phase matching (QPM) materials, PPLN suffers from a limited transparency, strongly limiting both the output power and the beam quality above 4 mum. We are developing a new QPM technology based on Orientation- Patterned Gallium Arsenide (OP-GaAs) crystals, transparent up to 16 mum and showing excellent nonlinear and thermal properties and very low losses (
[Show abstract][Hide abstract] ABSTRACT: We demonstrate what is to our knowledge the first realization of an optical parametric amplifier in orientation-patterned GaAs amplifying the emission of a quantum-cascade laser (QCL) with a distributed-feedback (DFB) structure. We report a gain as high as 53 dB at 4.5 mum, in good agreement with theoretical calculations. The narrow spectral linewidth and the good beam quality of this source are imposed by the DFB-QCL, while high-peak-power emission is achieved through the parametric amplification. These characteristics are of valuable interest for long-range spectroscopy.
[Show abstract][Hide abstract] ABSTRACT: A widely tunable difference frequency generation based mid-infrared spectrometer for the detection of sulfur dioxide (SO2), nitrous oxide (N2O), and methane (CH4) above 7 µm has been developed for industrial applications.
Laser Applications to Chemical, Security and Environmental Analysis; 01/2010
[Show abstract][Hide abstract] ABSTRACT: The effects of coupling between clockwise and counterclockwise modes in ring resonators due to back reflections from QPM gratings
in nonlinear crystals are investigated. We demonstrate, using simulations, that the non-phase-matched back reflection due
to typical imperfections of the QPM grating has a relevant magnitude and can give rise to the coupling. We developed an analytical
model and evaluated parameters of a singly resonant OPO in the presence of this coupling, which indicates that the threshold
pump power is doubled in the limit of strong coupling. We also evaluated the effect of the coupling with respect to resonant
power enhancement for cavity-enhanced nonlinear frequency mixing applications, finding that the enhancement is reduced by
up to a factor four. Experimental observations based on PPLN and orientation-patterned GaAs crystals and model predictions
are in good agreement. We propose and demonstrate a method for active stabilization of ring resonators with mode coupling
that relies on the dissimilarity of the coupled forward and backward modes.
Applied Physics B 01/2010; 100(4):737-747. · 1.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this article we address the design and exploitation of a real field laboratory demonstrator combining active polarimetric and multispectral modes in a single acquisition. Its buildings blocks, including a multi-wavelength pulsed optical parametric oscillator at emission side, and a hyperspectral imager with polarimetric capability at reception side, are described. The results obtained with this demonstrator are illustrated on some examples and discussed.
[Show abstract][Hide abstract] ABSTRACT: We report on the design and exploitation of a real-field laboratory demonstrator combining active polarimetric and multispectral functions. Its building blocks, including a multiwavelength pulsed optical parametric oscillator at the emission side and a hyperspectral imager with polarimetric capability at the reception side, are described. The results obtained with this demonstrator are illustrated on some examples and discussed. In particular it is found that good detection performances rely on joint use of intensity and polarimetric images, with these images exhibiting complementary signatures in most cases.
[Show abstract][Hide abstract] ABSTRACT: Toward efficient generation of tunable IR signals by quasi-phase-matched nonlinear optical frequency conversion, orientation-patterned GaAs crystals (OP-GaAs) were grown by hydride vapor phase epitaxy on lithographically prepared templates. The cathodoluminescence technique was used to study these epitaxial thick films, consisting of periodic domains of inverted crystallographic orientation, (001)/(00−1). The distribution of the main defects incorporated during growth is presented. One demonstrates that point defects, such as VGa complexes, can contribute to the optical losses of thick OP-GaAs crystals.
[Show abstract][Hide abstract] ABSTRACT: A narrow-linewidth mid-IR source based on difference-frequency generation of an amplified 1.5 microm diode laser and a cw Tm-doped fiber laser in orientation-patterned (OP) GaAs has been developed and evaluated for spectroscopic applications. The source can be tuned to any frequency in the 7.6-8.2 microm range with an output power of 0.5 mW. The measured characteristics of the OP-GaAs sample demonstrate a high quality of the material.
[Show abstract][Hide abstract] ABSTRACT: Nonlinear optical materials play a key role in the development of coherent sources of radiation as they permit the frequency conversion of mature solid-state lasers into spectral ranges where lasers do not exist or perform poorly. The availability of efficient quasi-phasematched infrared materials is thus considered as important for the development of several optronics applications. This paper will review the recent progresses achieved with thick Orientation-Patterned GaAs structures. We will present results obtained in growing a 500 mum thick layer on 2 cm long structures with low optical losses (less than 0.02 cm-1). This loss coefficient is low enough to allow the operation of a highly efficient GaAs OPO in the Mid-IR range.
[Show abstract][Hide abstract] ABSTRACT: To enhance discrimination of UV-laser-induced-fluorescence based bio-aerosol-detection-system, a UV-laser is described that allows multiple wavelength excitation of bio-aerosols and both fluorescence spectral and time-decay analysis. The latter requiring sub-ns pulse duration, a two-stage-amplifier boosts a 20-µJ-1064-nm-500-ps-actively-Q-Switch microchip-oscillator output energy up to 2.5 mJ. After frequency doubling and beam splitting, 20-µJ-293-and-337-nm pulses are generated by two different periodically-poled-KTP (parametric generation) and BBO (frequency doubling) crystal arrangements. In order to get distinct fluorescence signals for each wavelength, the beams are then time-delayed with two optical fibers of different lengths and launched into a chamber for bio-aerosol excitation connected to a fast detection system.
[Show abstract][Hide abstract] ABSTRACT: Nonlinear optical materials play a key role in the development of coherent sources of radiation as they permit the frequency conversion of mature solid-state lasers into spectral ranges where lasers do not exist or perform poorly. The availability of efficient quasi-phasematched infrared materials is thus considered as important for the development of several defense optronics applications. This paper will review the recent progresses we achieved with thick Orientation Patterned-GaAs structures. We will present results obtained in growing thick-layer (500 µm) on 2 cm long structures with very low optical losses (less than 0.02 cm-1). This loss coefficient is low enough to allow the realization of a high power OPO in the MIR band.
[Show abstract][Hide abstract] ABSTRACT: We report on the modeling and demonstration of an efficient intracavity cascadedPPLN OPO which converts 20% energy from 1.064 textmum to three narrow bands in the 2-5 textmuwavelength range. We have fully modeled the power, pulse shape, spectrum of each wavelengthinvolved in the cascaded optical parametric processes. Spatio-temporal numerical simulation ofthese processes combined with simple thermal models provide a correct estimate of the selfinducedthermal lensing and efficiency saturation.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report on what is, to our knowledge, the highest efficiency (57 %) and average power (1.2 W) obtained with a GaAs OPO in the mid-infrared region (3-5 mum). These results have been demonstrated thanks to the development of a low-optical-losses orientation-patterned GaAs (OP-GaAs) fabrication process. Our orientation-patterned quasiphase matching structures were produced by bonding together two 2" GaAs wafers. Standard photo-lithography and etching processes can then be used to define multi-grating 2-inches wafer.