Transfer function approach to collective mode dynamics in a Nd:YAG laser

For a multimode laser operating in a steady state regime with small-signal gain modulation, transfer functions are measured for both total intensity and intensities of individual modes. A quantitative picture of the phase clustering of contributions from each cavity mode to the collective mode dynamics is obtained from the transfer functions in the pole-residue representation.Stamatescu, L. Hamilton, M. W

A gain-coefficient switched Alexandrite laser

We report on a gain-coefficient switched Alexandrite laser. An electro-optic modulator is used to switch between high and low gain states by making use of the polarization dependent gain of Alexandrite. In gain-coefficient switched mode, the laser produces 85 ns pulses with a pulse energy of 240 mJ at a repetition rate of 5 Hz.Comment: 8 pages, 5 figure

Solving the riddle of codon usage preferences: a test for translational selection

Translational selection is responsible for the unequal usage of synonymous codons in protein coding genes in a wide variety of organisms. It is one of the most subtle and pervasive forces of molecular evolution, yet, establishing the underlying causes for its idiosyncratic behaviour across living kingdoms has proven elusive to researchers over the past 20 years. In this study, a statistical model for measuring translational selection in any given genome is developed, and the test is applied to 126 fully sequenced genomes, ranging from archaea to eukaryotes. It is shown that tRNA gene redundancy and genome size are interacting forces that ultimately determine the action of translational selection, and that an optimal genome size exists for which this kind of selection is maximal. Accordingly, genome size also presents upper and lower boundaries beyond which selection on codon usage is not possible. We propose a model where the coevolution of genome size and tRNA genes explains the observed patterns in translational selection in all living organisms. This model finally unifies our understanding of codon usage across prokaryotes and eukaryotes. Helicobacter pylori, Saccharomyces cerevisiae and Homo sapiens are codon usage paradigms that can be better understood under the proposed model

Quantum noise limits to simultaneous quadrature amplitude and phase stabilization of solid-state lasers

A quantum mechanical model is formulated to describe the coupling between pump intensity noise and laser frequency noise in a solid-state laser. The model allows us to investigate the limiting effects of closed-loop stabilization schemes that utilize this coupling. Two schemes are considered: active control of the quadrature phase noise of the laser and active control of the amplitude noise of the laser. We show that the noise of the laser in the actively stabilized quadrature is ultimately limited by the vacuum noise introduced by the feedback beamsplitter in both schemes. In the case of active control of the quadrature phase noise, the noise is also limited by the intensity noise floor of the detection scheme. We also show that some sources of noise in the passively stabilized quadrature can be suppressed and that it is possible to achieve simultaneous quadrature amplitude and phase stabilization of a solid-state laser. However, the quantum mechanically driven noise in the passively stabilized quadrature cannot be suppressed. While this poses the ultimate limit to the noise in the passively stabilized quadrature, we show that it is experimentally feasible to observe squeezing directly generated by a solid-state laser using this technique

Thermal lensing-induced bifocusing of spatial solitons in Kerr-type optical media

Thermo-optical effects cause a bifocusing of incoming beams in optical media, due to the birefringence created by a thermal lens that can resolve the incoming beams into two-component signals of different polarizations. We propose a non-perturbative theoretical description of the process of formation of double-pulse solitons in Kerr optical media with a thermally-induced birefringence, based on solving simultaneously the heat equation and the propagation equation for a beam in a one-dimensional medium with uniform heat flux load. By means of a non-isospectral Inverse Scattering Transform assuming an initial solution with a pulse shape, a one-soliton solution to the wave equation is obtained that represents a double-pulse beam which characteristic properties depend strongly on the profile of heat spatial distribution.Comment: 5 pages, 2 figure