Novel concepts in laser detection technology

Abstract

The objective of this thesis is to design and develop a low-cost sensing device capable of detecting Continuous Wave (CW) visible lasers. As lasers are widely used and potentially harmful in military and civilian contexts, such a device would be used to both detect lasers and gather laser characteristics before proper countermeasures can be taken.  This thesis has two experimental approaches. The first approach aims at improving the field of view of an already researched technology - a modified Mach-Zehnder (MZ) interferometer - in order to extend the practicability of the system. The second approach is the design of a novel concept of laser detection with the purpose of discriminating lasers from background light and characterizing the laser wavelength. In the case of the MZ system, a cone mirror is added to widen the initial horizontal field of view of ±3° while the additional use of a camera allows the direction of the incoming laser beam to be studied. The preliminary results demonstrate that a 360° horizontal field of view can be achieved, and that the direction of the laser beam can be determined with an estimated angular precision of ±5°. The system trades sensitivity for a larger field of view with the resultant detection sensitivity equal to 70 nW (or 1 μW.cm−2) at 635 nm. The second system is composed of Fresnel Zone Plates (FZP) digitally written on a Digital Micromirror Device (DMD) with the use of Zernike polynomials. The polynomials are also used to correct optical aberrations inherent to the system with the use of a camera for optical feedback. Four laser wavelengths have been characterized and the system reaches a relative wavelength resolution of 10−3, better than most of the detection systems using diffraction gratings.  Additionally, the structure of the system creates a strong coherence difference and helps discriminate high coherent sources against low coherent sources. This technology allows for a low-cost approach for CW visible laser detection and the detection is almost instantaneous.  Additionally, there are possibilities to extend the current detection system to NIR detection and pulsed lasers.