Andre Parent

Effects of hard apertures on mode properties of resonators with gaussian reflectivity mirrors

The effects of hard apertures on the energy distribution, the far-field beam quality, the mode volume, and the discrimination against high-order modes in Cassegrain resonators with Gaussian reflectivity mirrors have been investigated both theoretically and experimentally. It has been shown that, in the far field, the fraction of energy in the secondary lobes remains small as long as the ratio of the design beam waist to the radius of the gain medium w_{b}/a is w_{b}/a > 0.7 , deterioration of the beam quality and diffraction losses counterbalanced a more efficient filling of the gain medium to limit the resonator efficiency. At low magnifications, resonators with Gaussian mirrors out perform resonators with Standard mirrors.

Variable reflectivity unstable resonators for coherent laser radar emitters

Beam properties obtained from a TE CO(2) laser in a Cassegrain resonator using various graded reflectivity mirror couplers are compared. It is shown that, experimentally, Gaussian profiles maximize the far-field intensity while parabolic profiles yield more uniform near fields with a lower energy extraction. Both configurations appear suited for coherent ladar systems.

A compact wide-aperture single-mode TE-CO 2 laser with a low chirp rate

Single mode operation of a TE-CO 2 laser was obtained using a 2 \times 2 \times 30 cm gain module in a Cassegrain resonator with a Gaussian reflectivity convex mirror to produce a fundamental mode of large cross sectional area, and reducing the pressure to 375 torr in a 50 cm long cavity to limit the oscillation to a single longitudinal mode. The 70 ns gain switched pulse (FWHM) had an energy of 175 mJ, a peak power of 2.0 MW, a diffraction limited far-field, and a frequency chirp rate lower than 60 kHz/μs2.

Active range-gated near-IR TV system for all-weather surveillance

Adverse weather, lack of background illumination and interference from artificial light sources can considerably reduce the effectiveness of passive LLLTV systems. Viewing in such conditions can be considerably enhanced by the addition of a pulsed laser illuminator synchronized to a gated LLLTV. Since the system has its own light source, surveillance is possible in zero or ultra-low light conditions. Furthermore using the technique of range gating, the effects of backscattering that occur in poor visibility conditions can be greatly reduced. The high resolution and self-illumination capability of the system permits positive identification of targets that would be undetectable or unresolvable with FLIR type systems.

Mode Control In Unstable Cassegranian Resonators

In this paper, we present an overview of different laser resonator configurations leading to smooth single transverse mode of large cross sectional area. Particular attention is given to Cassegranian resonators in which one of the mirror has a radially varying reflectivity profile. Experimental results obtained with TE-CO2 lasers are discussed. It is shown that graded reflectivity mirrors are particularly well suited to frequency stable laser emitters in coherent lidar applications.

Tunable gain-switched chromium YAG laser

1.5 MW, < 10 nsec long gain-switched laser pulses were obtained from a Nd+3 laser-pumped Cr+4:YAG laser with an efficiency of 16%. Tuning was achieved from 1.44 to 1.51 micrometers . Repetition rate of 30 pps was demonstrated at approximately equals 10 mJ/pulse.

Laser-diode array collimation for scene illumination purposes

During the last five years, INO has conducted a program to develop high performance diode laser illuminator for ATV (active TV) system. Illuminator made using INO proprietary collimating method, which uses GRIN (mu) -lenses for the fast axis and plano-convex (mu) -lenses for the slow axis, were found to provide uniform and tightly collimated beam, diffraction-limited for the fast axis. Such collimated laser diode arrays were proven to efficiently illuminate non- cooperative scene at 1 km with only 6 W of average power.

Diffraction-limited Nd:glass and alexandrite lasers using graded reflectivity mirror unstable resonators

A high reflectivity, graded reflectivity mirror (GRM) design has been recently developed for use in low-gain lasers. A GRM with 63% central reflectivity was used as an output coupler in a low magnification (M equals 1.4) unstable resonator Nd:Glass laser to obtain a Q-switched energy of 2 J in a 25 ns pulse and over 3.7 J in fixed-Q operation. The beam has a diffraction limited divergence of 0.15 mrad. In an Alexandrite laser, a GRM having a central reflectivity of 78% was used in a M equals 1.2 unstable resonator. A fixed-Q output energy of over 500 mJ and a Q-switched energy of 400 mJ was obtained in a diffraction-limited beam. The second harmonic output was increased by a factor of ten from that obtained with a multimode stable resonator.