François Babin

Study of the aerodynamic trap for containerless laser materials processing in microgravity

In the context of containerless laser processing of glasses in microgravity, a systematic study of the aerodynamic trap (ADT) has been done on the ground at both ambient and very high temperatures (≳2000 K). This work yielded a better understanding of the ADT and helped in improving its design. Experiments indicate that restoring force and sample stability depend upon the diffuser’s interior angle, flow rate, and ratio of sample to diffuser’s throat diameters. It was found that the trap’s potential energy curve versus position had a barrier height that increased with flow rate but decreased with increasing angle of the diffuser. Small angle diffusers show a greater spatial extent of the potential well, higher sphere‐to‐wall distances, and greater sample stability than larger angle diffusers. Low flow rates give quieter environments (smaller oscillations and perturbations due to the gas flow) than higher flow rates even though they are sufficient to trap the sample and damp external perturbations. Heat los...

Standoff detection of explosives: a challenging approach for optical technologies

Standoff detection of explosives residues on surfaces at few meters was made using optical technologies based on Raman scattering, Laser-Induced Breakdown Spectroscopy (LIBS) and passive standoff FTIR radiometry. By comparison, detection and analysis of nanogram samples of different explosives was made with a microscope system where Raman scattering from a micron-size single point illuminated crystal of explosive was observed. Results from standoff detection experiments using a telescope were compared to experiments using a microscope to find out important parameters leading to the detection. While detection and spectral identification of the micron-size explosive particles was possible with a microscope, standoff detection of these particles was very challenging due to undesired light reflected and produced by the background surface or light coming from other contaminants. Results illustrated the challenging approach of detecting at a standoff distance the presence of low amount of micron or submicron explosive particles.

Use of a spectroscopic lidar for standoff explosives detection through Raman spectra

This paper assesses the potential of detecting explosives (RDX, TNT, PETN, HMX, HMTD, Urea Nitrate) from a distance with a spectroscopic lidar system. For the study, the temporal and spectral resolutions of laser induced fluorescence lidar prototypes were enhanced. The integrated breadboards used easily available Nd:YAG laser wavelengths (266 nm, 355 nm, and 532 nm) to remotely detect the Raman signatures induced in traces of explosives deposited on surfaces. The spectroscopic lidar setup allows for time resolved measurements with high temporal resolution. Raman spectra are observable, even in the presence of fluorescence. Experiments with low average laser power (tens of mWs) have shown the unambiguous capability to detect and identify explosives at distances ranging up to 20 m. Thanks to the combination of UV wavelength for higher Raman cross-sections and efficient gated detection the 355 nm prototype yielded the best compromise. Excitation at 266 nm was expected to yield a better Raman response and was investigated. Less than optimal laser parameters, detection efficiency and strong fluorescence reduced the signal to noise ratio of the 266 nm signals with respect to those at 355 nm and 532 nm showing the importance of optimizing system parameters for high sensitivity detection. Besides the description of the prototypes and an early assessment of their performances, recommendations are also proposed to improve the instrument, leading to an efficient remote sensor for explosives.

Broadband and tunable optical parametric generator for remote detection of gas molecules in the short and mid-infrared.

The development of a novel broadband and tunable optical parametric generator (OPG) is presented. The OPG properties are studied numerically and experimentally in order to optimize the generators use in a broadband spectroscopic LIDAR operating in the short and mid-infrared. This paper discusses trade-offs to be made on the properties of the pump, crystal, and seeding signal in order to optimize the pulse spectral density and divergence while enabling energy scaling. A seed with a large spectral bandwidth is shown to enhance the pulse-to-pulse stability and optimize the pulse spectral density. A numerical model shows excellent agreement with output power measurements; the model predicts that a pump having a large number of longitudinal modes improves conversion efficiency and pulse stability.

Enhancements to INO's broadband SWIR/MWIR spectroscopic lidar

Recent advances in the INO broadband SWIR/MWIR spectroscopic lidar will be presented. The system is designed for the detection of gaseous pollutants via active infrared differential optical absorption spectroscopy (DOAS). Two distinctive features are a sub-nanosecond PPMgO:LN OPG capable of generating broadband (10 to <100 nm FWHM) and tunable (1.5 to 3.8 μm) SWIR/MWIR light, and an in-house gated MCT-APD focal plane array used in the output plane of a grating spectrograph. The operation consists in closely gating the returns from back-scattering off topographic features, and is thus, for now, a path integrated measurement. All wavelengths are emitted and received simultaneously, for low concentration measurements and DOAS fitting methods are then applied. The OPG approach enables the generation of moderate FWHM continua with high spectral energy density and tunable to absorption features of many molecules. Recent measurements demonstrating a minimum sensitivity of 10 ppm-m for methane around 3.3 μm with ∼ 2 mW average power in less than 10 seconds will be described. Results of enhancements to the laser source using small or large bandwidth seeds constructed from telecom off-the-shelf components indicate that the OPG output spectral energy density can have controllable spectral widths and shapes. It also has a slightly more stable spectral shape from pulse to pulse than without the seed (25 % enhancement). Most importantly, the stabilized output spectra will allow more sensitive measurements.

Latest developments in active remote sensing at INO

Remote sensing or stand-off detection using controlled light sources is a well known and often used technique for atmospheric and surface spatial mapping. Today, ground based, vehicle-borne and airborne systems are able to cover large areas with high accuracy and good reliability. This kind of detection based on LiDAR (Light Detection and Ranging) or active Differential Optical Absorption Spectroscopy (DOAS) technologies, measures optical responses from controlled illumination of targets. Properties that can be recorded include volume back-scattering, surface reflectivity, molecular absorption, induced fluorescence and Raman scattering. The various elastic and inelastic backscattering responses allow the identification or characterization of content of the target volumes or surfaces. INO has developed instrumentations to measure distance to solid targets and monitor particles suspended in the air or in water in real time. Our full waveform LiDAR system is designed for use in numerous applications in environmental or process monitoring such as dust detection systems, aerosol (pesticide) drift monitoring, liquid level sensing or underwater bathymetric LiDARs. Our gated imaging developments are used as aids in visibility enhancement or in remote sensing spectroscopy. Furthermore, when coupled with a spectrograph having a large number of channels, the technique becomes active multispectral/hyperspectral detection or imaging allowing measurement of ultra-violet laser induced fluorescence (UV LIF), time resolved fluorescence (in the ns to ms range) as well as gated Raman spectroscopy. These latter techniques make possible the stand-off detection of bio-aerosols, drugs, explosives as well as the identification of mineral content for geological survey. This paper reviews the latest technology developments in active remote sensing at INO and presents on-going projects conducted to address future applications in environmental monitoring.

Active 3D camera design for target capture on Mars orbit

During the ESA Mars Sample Return (MSR) mission, a sample canister launched from Mars will be autonomously captured by an orbiting satellite. We present the concept and the design of an active 3D camera supporting the orbiter navigation system during the rendezvous and capture phase. This camera aims at providing the range and bearing of a 20 cm diameter canister from 2 m to 5 km within a 20° field-of-view without moving parts (scannerless). The concept exploits the sensitivity and the gating capability of a gated intensified camera. It is supported by a pulsed source based on an array of laser diodes with adjustable amplitude and pulse duration (from nanoseconds to microseconds). The ranging capability is obtained by adequately controlling the timing between the acquisition of 2D images and the emission of the light pulses. Three modes of acquisition are identified to accommodate the different levels of ranging and bearing accuracy and the 3D data refresh rate. To come up with a single 3D image, each mode requires a different number of images to be processed. These modes can be applied to the different approach phases. The entire concept of operation of this camera is detailed with an emphasis on the extreme lighting conditions. Its uses for other space missions and terrestrial applications are also highlighted. This design is implemented in a prototype with shorter ranging capabilities for concept validation. Preliminary results obtained with this prototype are also presented. This work is financed by the Canadian Space Agency.

70-nm tunable single-longitudinal mode erbium-doped fiber laser

This paper presents experimental results on a 70-nm-wide, quasi-continuously tunable, single-longitudinal-mode erbium-doped fiber (EDF) laser. The cavity incorporates three tunable band-pass filters; a bulk grating based tunable band-pass filter, a fiber-ring-cavity filter, and an auto-tracking saturable absorption induced grating filter generated by an un-pumped EDF. In our experiment, this laser produced a single longitudinal mode oscillation between 1510 nm and 1580 nm, an output power of 0.5 mW and a tuning step of less than 0.2 pm. Optical frequency jitter was less than 0.8 pm and the signal to source spontaneous emission ratio (S/SSE) was higher than 60 dB. A tunable single-longitudinal-mode L-band fiber laser will also be discussed in this paper.

Broadband spectroscopic lidar for SWIR/MWIR detection of gaseous pollutants in air

A broadband SWIR/MWIR spectroscopic lidar for detection of gaseous pollutants in air is presented for doing differential optical absorption spectroscopy (DOAS). One of the distinctive parts of the lidar is the use of a picosecond PPMgO:LN OPG (optical parametric generator) capable of generating broadband (10 to <100 nm FWHM) and tunable (1.5 to 3.9 μm) SWIR/MWIR light. The optical source layout and properties are presented, along with a description of the lidar breadboard. Results from indoor simulated typical operation of the lidar will be discussed, the operation consisting in emitting the broadband coherent light along a line of sight (LOS) and measuring the back-scattering returns from of a topographic feature or aerosols. A second distinctive part is the gated MCT-APD focal plane array used in the output plane of the grating spectrograph of the lidar system. The whole of the returned spectra is measured, within a very short time gate, at every pulse and at a resolution of a few tenths to a few nm. Light is collected by a telescope with variable focus for maximum coupling of the return to the spectrograph. Since all wavelengths are emitted and received simultaneously, the atmosphere is “frozen” during the path integrated measurement and hopefully reduces the baseline drift problem encountered in many broadband scanning approaches. The resulting path integrated gas concentrations are retrieved by fitting the molecular absorption features present in the measured spectra. The use of broadband pulses of light and of DOAS fitting procedures make it also possible to measure more than one gas at a time, including interferents. The OPG approach enables the generation of moderate FWHM continua with high spectral energy density and tunable to absorption features of a great number of molecules. Proposed follow-on work and applications will also be presented.

Proposal for a standoff bio-agent detection SWIR/MWIR differential scattering lidar

A SWIR/MWIR spectroscopic lidar is proposed for standoff bio-agent cloud detection using simultaneous broadband differential scattering (DISC). Measurements and/or modeling of DISC spectra of simulants are revisited and the rational of the SWIR/MWIR DISC approach is explained, especially in light of the LWIR DISC experiments and conclusions done elsewhere. Preliminary results on the construction of a low power non-linear broadband source in the SWIR/MWIR are presented. Light from a 1064-nm pump laser is passed through a period and temperature tunable PPMgO:LN Optical Parametric Generator (OPG) to generate broadband light with a full width at half maximum (FWHM) of 10 to >100 nm in the SWIR/MWIR between 1.5 and 3.9 μm. Broadband coherent light from this source is to be emitted towards a cloud that generates back-scattering. This source is being used in a short-range chemical remote detection breadboard, showing the possible dual use of the setup. Light collected by the receiver telescope is coupled to a grating spectrometer and the return signal (DISC in the proposed setup) is detected using a gated MCT-APD array in much the same way clouds are interrogated using UV-LIF. A programmable volume of space along the laser beam path is imaged at the entrance of the spectrometer and 320 spectral channels can be measured simultaneously, attenuating the effects of atmospheric instabilities on DISC measurements. Proposed follow-on work will be presented.