P. A. Belanger

Complex index of refraction of dental enamel at CO 2 laser wavelengths

The reflectance vs angle of incidence method was used to determine the refractive index and absorption coefficient of dental enamel at CO(2) laser wavelengths. A strong wavelength dependence of the optical constants was observed in this spectral region which corresponds to a well-known absorption band of hydroxyapatite, the main constitutent of dental enamel. A directional dependence of the optical constants of dental enamel was also observed. The absorption coefficient reaches a maximum between 9.75 and 10 microm. This particularity may be important for the main CO(2) laser treatments proposed in dentistry up to now: surface treatment of teeth and fusion of dental materials.

Self-focusing of Gaussian beams: an alternate derivation

It is shown that self-focusing can be taken into account in an optical paraxial system by simply defining a new generalized radius of curvature, namely, 1qNL=1R−jσπW2λ,where (σ − 1) is the ratio of the power of the beam to the critical power for self-focusing.

Single-longitudinal-mode operation of a TEA CO 2 laser with a modified Fabry-Perot interferometer

An interferometric device consisting of two metallic mirrors and a dielectric beam splitter of low reflectivity is used to reduce the spectral emission of a CO2 TEA laser to a single longitudinal mode (SLM). The finesse of the interferometer can be varied continuously by turning the polarization of the laser beam or in steps by using different beam splitters. The resonant reflectivity of the device was found to vary from 20 to 90% depending on transverse mode matching and alignment. With a low reflectivity beam splitter, the reliability of producing SLM pulses reached 100%. As the beam splitter reflectivity was increased, the interferometer finesse decreased resulting in a low reliability of producing SLM pulses. The maximum free spectral range which gave SLM reliably was 5 GHz. We also replaced one of the mirrors of the interferometer by a grating, and we observed SLM output on forty lines of the CO2 spectrum with a reproducibility of 80% or better. We discuss how the device could be used for intracavity pulse selection.

Transverse modes of a stimulated scattering phase-conjugate resonator

Gaussian transverse eigenmodes of a stimulated scattering phase-conjugate resonator are calculated. The experimental setup which provides the stimulated scattering phase-conjugate resonator is described.

Modes of phase-conjugate resonators with bounded mirrors

The diffraction losses of phase-conjugate resonators with bounded mirrors are shown to depend only on two dimensionless parameters. The hemispherical phase-conjugate resonator is shown to yield a fundamental mode with minimum loss among all phase-conjugate resonators with the same mirror dimensions. Proof is given that the diffraction losses around the phase-conjugate mirror are larger than the diffraction losses around the conventional mirror; hence diffraction coupling is more efficient around the phase-conjugate mirror. Numerical results support these conclusions.

Single Longitudinal Mode Operation Of A Continuously Tunable High Pressure TE-CO2 Laser

A modified Fabry-Perot interferometer along with a thin tilted etalon has been used successfully to obtain single longitudinal mode pulses from a 10 atmosphere pressure CO2 laser. Reliability of 85% was observed for cavity lengths up to 2.8 meters. Continuous tuning over a frequency range of 15 cm-1 was obtained on both the R and the P branches of the 9 μm and 10 μm transitions using a grating.

Single longitudinal mode operation of a tunable traveling-wave tea-CO2 laser

Abstract Single mode operation of a ring cavity TEA-CO 2 laser was achieved using an interferometer consisting of two beam splitters positioned between two metallic mirrors. The relative amplitudes of the counter-propagating waves are fixed once the reflectivities of the beam splitters are chosen. There is no ambiguity as to the direction of propagation.

Losses of phase-conjugate resonators: directional behavior in aberrated multiaperture cavities

The directional behavior of power losses in aberrated multiaperture optical resonators with one or two phase-conjugate mirrors is investigated through integral equations and the reciprocity theorem. In a resonator with one phase-conjugate mirror, the losses of the mode traveling from the conventional mirror to the phase-conjugate mirror are shown to be larger than the losses of the counterpropagating mode. In a resonator with two phase-conjugate mirrors, the losses along each direction are found to be equal.

Transverse mode-locking by short pulse injection in large aperture TEA CO 2 oscillators

Single short pulses were injected in TEA-CO(2) laser cavities made of two copper mirrors. Simultaneous longitudinal and transverse mode-locking was evidenced by periodic focusing of the internal short pulse. The focusing action could be eliminated by short train injection.