Analysis Of Laser Research Articles

Analysis of Lasing From Direct Transition in Ge-on-Si

This paper describes a theoretical investigation of lasing from the direct, Γ-point transition in bulk germanium grown on silicon substrate. Relationships between desired gain and required current density are computed using a screened Hartree- Fock gain model for structures of different tensile strains and n-doping densities. The calculations indicate that for unstrained Ge, high free-carrier absorption and gain saturation may lead to no positive net gain regardless of excitation. With 0.2% tensile strain, the theory predicts possible lasing under laboratory conditions, but uncertainties in free-carrier absorption and Auger losses make difficult definitive predictions for a practical device. Results for 0.6% tensile strain and > 1019 cm-3 n-doping gives a more definitive prediction of constant wave lasing with threshold current density of ~1 kA/cm2.

Analysis of Lasing in Dye-Doped Photonic Crystals

Recently, we experimentally demonstrated room-temperature lasing of self-assembled opal photonic crystal (PhC) made of rhodamine-B-doped polystyrene colloids. Here, we explain this experimental observations by analyzing the phenomenon of light amplification in dye-activated PhCs via a complex-valued permittivity of the colloids. We show that the lasing is facilitated by the enhanced distributed feedback due to the reduced group velocity in the vicinity of the photonic band edge. This simple approach to the analysis of PhC lasing behavior allows us to calculate the lasing wavelength in close agreement with the experimental value. It also enables the estimation of gain coefficient required for lasing and may prove useful in design of compact PhC-based lasers.

Analysis of lasing in gain medium based on four-energy level atomic model

With the present interest in metamaterial, gain medium shows promise for complex system due to their amplification effect and wide potential application area. In this paper we present a model that simulates lasing in gain medium by using a model of four-energy level atomic system based on the finite-difference time-domain method.Meanwhile we propose a new pump mechanism, i.e., Gaussian Pump. It is found that results of the spectra, lasing threshold and population dynamics of the new pump mechanism are in good agreement with theoretical results. The results can also provide reference for caculating more complex metamaterial system.

An analysis of lasing without inversion in a three level system in terms of vector representation

In the present work, we show that the problem of Λ-type three level systems and lasing without inversion can be understood in terms of evolution of vectors. The time evolutions of these vectors have been worked out using the transition probabilities and detuning. One of the salient features of the work is that Glauber-Sudershan’s p-function can be visualized with this approach. We also present a comparative study between different vector models representing three level Λ-type lasers.

An analysis of lasing without inversion in a three level system in terms of vector representation

In the present work we have worked out phasor diagrams with the help of the concept of moving vectors. We show that the area enclosed by the phasor diagrams behaves like lifetime of atomic states. We also make a comparative study of our model with the models suggested by other workers to explain lasing without inversion.

Analysis of lasing in chemical oxygen-iodine lasers with unstable resonators using a geometric-optics model

A simple geometric-optics model is developed that describes the power extraction in chemical oxygen-iodine lasers (COILs) with unstable resonators. The positive and negative branch unstable resonators with cylindrical mirrors that were recently used in COILs are studied theoretically. The optical extraction efficiency, spatial distributions of the intracavity radiation intensity in the flow direction, and the intensity in the far field are calculated for both kinds of resonator as a function of both the resonator and the COIL parameters. The optimal resonator magnifications that correspond to the maximum intensity in the far field are found.

Towards XUV lasers with charge transfer pumping

Detailed studies of charge exchange pumping of ions in femtosecond laser-produced plasmas colliding with a pulsed gas jet are presented. Strong selective excitation of XUV ionic transitions in the reaction C4++H→C3++H+ is observed. Dependences of line intensities on various experimental parameters are reported which are in good agreement with the theory of charge transfer processes. Analyses of experimental data provide evidence that an efficient charge exchange pumping is realized at densities of reagents well in excess of 1016 cm−3, which is essential for the realization of XUV lasers. In preliminary investigations of the reaction C6++H→C5+ (n=3,4)+H+ a strong increase of line intensities at 13.5 and 18.2nm is reported. Analysis of lasing in Na-like ions with an example for Chlorine promises even more efficient pumping as compared with the before analyzed hydrogen like ions.

Analysis of lasing in gas-flow lasers with stable resonators

A model is developed that describes the power extraction in chemical oxygen-iodine lasers (COIL's) and CO(2) gasdynamic lasers with stable resonators when a large number of transverse Hermite-Gaussian eigenmodes oscillate. The extraction efficiency, mode intensities, and intensity distribution along the flow depend only on two parameters. The first is the ratio gamma(0) of the residence time of the gas in the resonator to the O(2)((1)D) or N(2)(v) energy extraction time and the second is the ratio of the threshold to the small-signal gain. The efficiency is maximum for gamma(0) ? infinity and decreases rapidly as gamma(0) decreases. It is found that for a range of parameters corresponding to the highest efficiencies the intensity distribution along the flow is nonuniform and has two peaks near the upstream and downstream sections of the resonator. In this case only the highest-order modes that totally fill the resonator cross section oscillate (the so-called, experimentally observed sugar scooping bimodal intensity distribution). For the range of parameters corresponding to smaller efficiencies the intensity is uniform. In this case all the modes participate in lasing; however, the intensities of the high-order modes are larger than those of the low order. The current model is compared with the plane-mirror Fabry-Perot resonator model and with the constant intraresonator intensity and rooftop models of COIL's with stable resonators. The extraction efficiency calculated with the last two models is close to that estimated from our model. However, the intensity distribution cannot be calculated correctly using the Fabry-Perot, the constant intraresonator intensity, or the rooftop model.