Optical resonators with variable reflectivity mirrors
TL;DR: This paper investigates circular optical resonators with gaussian profiles of the mirror reflectivities with closed form solution to the integral equations for such resonators obtained and presents a specific design of a Fabry-Perot resonator for fundamental mode operation and the expected performance.
Abstract: In this paper we investigate circular optical resonators with gaussian profiles of the mirror reflectivities. Closed form solution to the integral equations for such resonators are obtained. The dominant TEM o,o mode characteristics of a resonator consisting of one variable reflectivity mirror (VRM) and one uniform reflectivity mirror (URM) are considered in detail for a variety of parameters. This resonator is particularly suitable for high-gain lasers. Its advantages in comparison to the conventional type are: (i) there is larger mode volume utilization, and (ii) the power transmitted at the variable reflectivity mirror can in principle be utilized as the power output. We discuss dependence of the spot sizes on laser gain and mirror-curvature tolerances and present a specific design of a Fabry-Perot resonator for fundamental mode operation and the expected performance.
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TL;DR: It is concluded that for any laser system characterized by a moderate gain per pass and a Fresnel number greater than a few times unity the unstable resonator provides the best practical resonator design for obtaining a high-quality near-diffraction-limited output laser beam combined with efficient energy extraction from the laser medium.
Abstract: This paper reviews the current level of theoretical understanding and experimental confirmation of the properties of unstable optical resonators for laser oscillators. A primary conclusion is that for any laser system characterized by a moderate gain per pass and a Fresnel number greater than a few times unity the unstable resonator provides the best practical resonator design for obtaining a high-quality near-diffraction-limited output laser beam combined with efficient energy extraction from the laser medium.
261 citations
TL;DR: In this article, the authors investigated plasma formation in distilled water by 30-ps and 6-ns Nd:YAG laser pulses of 1064-nm and 532-nm wavelength for focusing angles between 1.7° and 32°.
Abstract: We investigated plasma formation in distilled water by 30-ps and 6-ns Nd:YAG laser pulses of 1064-nm and 532-nm wavelength for focusing angles between 1.7° and 32°. We determined the optical breakdown thresholds and analyzed the plasma length achieved at superthreshold irradiance, The parameter range investigated covers the parameters used for intraocular laser surgery. The experimental results are compared to theoretical models for the calculation of breakdown thresholds and the description of plasma growth for superthreshold breakdown. We found that at λ=1064 nm the measured thresholds for both pulse durations coincide with the calculated thresholds for the generation of seed electrons by multiphoton ionization. The breakdown process is completed by avalanche ionization. The seed electron density required for breakdown is about 4×10/sup 9/ cm for the 6-ns pulses, and 1.4×10/sup 11/ cm/sup -3/ for the 30-ps pulses. No spot size dependence of the irradiance threshold for breakdown was observed. The average threshold is by a factor of 5.9 higher for 30-ps pulses (I/sub th/=4.5×1011 W/cm2) than for 6-ns pulses (Ith=0.76×10/sup 11/ W/cm/sup 2/). At angles below approximately 2°, the threshold is influenced by self-focusing effects. The breakdown thresholds at 532 nm are slightly lower than at 1064 nm. Here, multiphoton ionization contributes considerably to the generation of free electrons throughout the whole process of plasma formation. Our results for plasma formation at superthreshold energies support a "breakdown wave" mechanism of plasma growth. For picosecond pulses, the breakdown threshold can be considered to be time-invariant, but for nanosecond pulses there is probably a decrease of the threshold during the laser pulse which may be due to UV-radiation emitted from plasma created at the beginning of the pulse.
249 citations
164 citations
TL;DR: Sinusoidal-Gaussian beam solutions for the propagation of electromagnetic waves in free space and in media having at most quadratic transverse variations of the index of refraction and the gain or loss were derived in this article.
Abstract: Sinusoidal-Gaussian beam solutions are derived for the propagation of electromagnetic waves in free space and in media having at most quadratic transverse variations of the index of refraction and the gain or loss. The resulting expressions are also valid for propagation through other real and complex lens elements and systems that can be represented in terms of complex beam matrices. The solutions are in the form of sinusoidal functions of complex argument times a conventional Gaussian beam factor. In the limit of large Gaussian beam size, the sine and cosine factors of the beams are dominant and reduce to the conventional modes of a rectangular waveguide. In the opposite limit the beams reduce to the familiar fundamental Gaussian form. Alternate hyperbolic-sinusoidal-Gaussian beam solutions are also found.
134 citations
Cites background from "Optical resonators with variable re..."
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TL;DR: The paper reviews the principles of nonlinear absorption with reference to the present major clinical applications of plasma-mediated effects: intraocular microsurgery and laser lithotripsy.
Abstract: The paper reviews the principles of nonlinear absorption with reference to the present major clinical applications of plasma-mediated effects: intraocular microsurgery and laser lithotripsy. Emphasis is laid on the analysis of the working mechanisms, sources of collateral damage, and on strategies for both the optimization of efficacy and the minimization of side effects.
132 citations