Gilles Fortin

Chirped holographic grating used as the dispersive element in an optical spectrometer

We have developed a new design of optical spectrometer based on the use of a chirped holographic grating inscribed on a flat substrate. This type of grating has a surface modulation with a spatially varying period. The ability of the chirped grating to focus a beam is exploited to reduce significantly the physical dimensions of the instrument. Wavelength selection is achieved by a pure translation of the chirped grating. The properties of the chirped grating spectrometer have been characterized with different lasers and arc lamps and compared with those of two commercial spectrometers. A performance parameter has been defined, enabling the various instruments to be compared.

Tuning of external-cavity semiconductor lasers with chirped diffraction gratings

We present a novel scheme of tunable semiconductor laser based on the use of a chirped grating in an external cavity. The chirped grating is fabricated using a simple holographic technique: two Gaussian beams having wavefronts with different radii of curvature are brought to interfere on a photoresist layer. The tuning properties of chirped gratings have been investigated with semiconductor lasers operated with an external cavity. With this type of grating positioned in Littrow configuration, the wavelength selection can be done by translating the grating without any need to rotate it. This cavity configuration provides a tunable output beam with an angle of propagation that is independent of the wavelength. The translation of chirped gratings was shown to tune a visible diode laser and an infrared diode laser over the same spectral band as the conventional tuning scheme where an unchirped grating is rotated.

BUBBLE: Relationship Diagrams Using Iterative Vector Approximation

The BUBBLE program generates relationship diagrams from a list of elements (rooms, peoples, functions, etc.) and a relationship matrix between these elements which specifies desirable distances. Every element is considered as a point in 2-D space in which vectors approximating the specified distances are applied. An equilibrium state is reached after a few iterations. Because the program can also take into account the size of elements and their orientation, it is a useful tool in preliminary architectural layout. The layout problem is described and the BUBBLE approach is stated and compared with other layout techniques such as enumeration, hill-climbing, build-up models, a detailed description of the algorithm is supplied. Some examples are discussed. Test-cases describe the efficiency and the limits of the approach. The program is currently being used by students in architecture to help them gain insight on using relationship matrices to solve preliminary layout problems.

Technique for continuous tuning of an extended-cavity diode laser

Mode-hop-free operation of an extended-cavity diode laser is achieved with an innovative technique. A chirped (varied-line-space) diffraction grating is used as an external coupler. Continuous tuning is obtained by a simple linear translation of the grating. The measured continuous tuning range is currently as wide as 37 nm (4.6 THz) near 1550 nm with a relatively constant output power.

A novel infrared hyperspectral imager for passive standoff detection of explosives and explosive precursors

The passive standoff detection of vapors from particular explosives and precursors emanating from a location under surveillance can provide early detection and warning of illicit explosives fabrication. DRDC Valcartier recently initiated the development and field-validation of a novel R&D prototype, MoDDIFS (Multi-Option Differential and Imaging Fourier Spectrometer) to address this security vulnerability. The proposed methodology combines the clutter suppression efficiency of the differential detection approach with the high spatial resolution provided by the hyperspectral imaging approach. This consists of integrating the imaging capability of the Hyper-Cam IR imager with a differential CATSI-type sensor. This paper presents the MoDDIFS sensor methodology and the first investigation results that were recently obtained.

4×4 ray matrix for a curved chirped grating at oblique incidence

The general 4x4 ray matrix of a grating is presented. This matrix suits the cases of transmission and reflection by a chirped grating with curved lines lying on a curved interface. The matrix presented applies to the general oblique incidence of the optical axis and therefore to nonorthogonal cases and to conical diffraction.

Standoff detection results with the infrared hyperspectral MoDDIFS sensor

The passive standoff monitoring of vapor precursors emanating from a location under surveillance can provide relevant information on the nature of products fabrication. Defence Research & Development Canada Valcartier recently completed the development and field-validation of a novel R&D prototype, MoDDIFS (Multi-option Differential Detection and Imaging Fourier Spectrometer), to address this remote sensing application. The proposed methodology combines the clutter suppression efficiency of the differential detection approach with the high spatial resolution provided by the hyperspectral imaging approach. This consists of integrating a differential CATSI-type (Compact ATmospheric Sounding Interferometer) sensor with the imaging capability of the Hyper-Cam infrared imager. The MoDDIFS sensor includes two configuration options, one for remote gas detection, and the other for polarization sensing of surface contaminants. This paper focuses on the infrared spectral detection of gases. A series of measurements done with MoDDIFS on selected laboratory solvents in vapor form are analyzed and discussed.

Continuous Tuning of a Diode Laser Over 8.4 THz Near 1550 nm With a Chirped Grating

We achieve mode-hop-free tuning of an extended-cavity diode laser with an original technique. The external coupler is a chirped (varied line-space) diffraction grating. A simple linear translation of the grating is then sufficient to obtain continuous tuning. The measured continuous tuning range has reached 66 nm (8.4 THz) near a wavelength of 1550 nm with a relatively constant output power of 3 mW.

Enhanced target detection and identification using multispectral and hyperspectral polarimetric thermal measurements

The performance of thermal electro-optic infrared sensors (EO/IR) may be limited in certain specific circumstances, particularly for the detection and identification of targets embedded in an isothermal scene, i.e. when there is insufficient thermal contrast between the targets against their surrounding background. Such situations generally occur at the beginning and end of the day, but can also happen at any time during the day. One way to cope with this limitation is to employ EO/IR sensors that are sensitive to the polarization states of light. With this intention, Defence Research and Development Canada (DRDC) has developed thermal infrared multispectral and hyperspectral polarimetric imaging systems and spectral algorithms to extract the polarized radiance components of targets of interest, and use this additional information to enhance detection and identification while reducing false alarm rate. This paper presents experimental results from measurements using ground-based multispectral and hyperspectral polarimetric imaging sensors to acquire the polarized radiance of targets set up at multiple orientation angles with respect to the sensors lineof-sight (LOS). The objectives of the experiments were to study the phenomenology of polarized surface radiance in the Long-Wave Infrared (LWIR) and assess the effect of different materials on the resulting s-polarized and p-polarized spectral components. Experimental results show the advantages of thermal multispectral and hyperspectral polarimetric imaging sensors over conventional unpolarized ones to discriminate targets against their background, particularly during thermal cross-over periods.

Hyperspectral gas and polarization sensing in the LWIR: Recent results with MoDDIFS

Imaging Fourier-transform infrared (FTIR) spectroscopy is a powerful method for the passive remote detection and identification of vapor emanations and surface contaminations. In the Defense and Security context, imaging FTIR can be used for the remote surveillance of locations suspected of illicit product fabrications. DRDC Valcartier recently initiated the development and field-validation of the novel imaging FTIR sensor MoDDIFS (Multi-option Differential Detection and Imaging Fourier Spectrometer) to address this remote sensing application. The proposed system combines the clutter suppression efficiency of the differential detection approach with the high spatial resolution provided by the hyperspectral imaging approach. The MoDDIFS sensor includes two configuration options, one for remote gas detection, and the other for polarization sensing of surface contamination. This paper reviews recent results obtained with MoDDIFS for the passive standoff detection of gases and liquid contaminants. Hyperspectral measurements done on difluoroethane, diethyl ether (gases) and SF96 (liquid) serve to develop, test and validate GLRT-type detection algorithms. Detection results are presented and discussed in terms of the GLRT detection attributes.