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Recent years have seen an increase of interest in developing nano-scale sources of coherent radiation. Numerous schemes includes novel confinement techniques such as plasmons and micro resonators as well as novel materials, such as two-dimensional transition metal di-chalcogenides have been investigated. In the process a lot of confusion has been produced by introduction into consideration of numerous parameters such as Purcell factor and the beta (fraction of spontaneous emission going into a given mode). That confusion makes comparative analysis of miniature lasers difficult. In this talk we show that the only parameters defining the laser threshold are the modal loss, quantum efficiency and physical volume of gain medium. Using this method we compare the novel lasers with existing state of the art – DFB and VCSELs and draw conclusions.

In the talk we will discuss the role of disorder-induced losses on the threshold of line-defect photonic crystal lasers. Experiments reveal an optimum cavity length, on the order of 10 unit cells, where the laser threshold density attains a minimum. The results can be explained by considering the role of slow-light propagation on the threshold of a photonic crystal laser. We will also discuss the possibility of alleviating this dependence on cavity length by replacing one of the mirrors with a narrow-band mirror based on a Fano resonance.

Random laser actions in a disordered media based on ethylene glycol doped with Rh6G dye and Au nanorods have been demonstrated. It was observed that the size of Au nanorods strongly affects the pump threshold. The experiment results suggesting that the random lasing properties are dominated by the surface plasmons.

Liquid crystal (LC) lasers have gained a lot of research interest in the last decade. Especially out-of-plane emitting chiral nematic liquid crystal (CLC) lasers have been studied extensively. These regular CLC lasers have a one-dimensional (1D) structure and the active cavity length is inherently limited. By using CLCs in two- and three-dimensional structures, the flexibility and applicability of the laser structures can be strongly enhanced. In this paper we focus on 2D in-plane emitting CLC lasers with a lying helix structure. We elaborate further on different techniques to obtain the lying helix structure and we analyze the lasing properties and compare these to regular 1D out-of-plane emitting CLC and NLC lasers. Both differences in emission spectrum, laser threshold, slope efficiency and maximal output energy are discussed.

In the assembly of optical resonators of optically pumped semiconductor lasers (OPSL), the highly reflective resonator mirror is the most crucial component. In previous cooperation, Coherent and Fraunhofer IPT have developed a robust active alignment strategy to optimize the output power of the OPSL resonator using search strategies for finding the laser threshold as well as hill-climbing algorithms for maximizing the output power. Beam-shape as well as the laser mode have major influence on the quality and the duration of subsequent beam-shaping and fiber-coupling steps. Therefore, the alignment algorithm optimizing the output power has been extended recently by simultaneous image processing for ensuring a Gaussian beam as the result of alignment. The paper describes the enhanced approach of automated alignment by additionally scanning along the optical resonator and subsequently evaluating and optimizing the roundness of the beam as well as minimizing the beam radius through twisting and tilting of the mirror. A quality metric combining these measures is defined substituting an M² measurement. The paper also describes the approach for automated assembly including the measuring setup, micromanipulation and dispensing devices.

The aim of the presented project was comparison of two Fe:ZnSe lasers based on Fe:ZnSe bulk active crystals grown by two different methods - Bridgman and floating zone. For pumping the Q-switched Er:YAG laser generating 15 mJ and 300 ns giant pulses was used. The highest Fe:ZnSe laser generated output energy was 1.2 - 1.3 mJ for both investigated crystals, the pulse duration was 150 - 200 ns. The Fe:ZnSe laser threshold was reached at absorbed pumping energy of ~ 1 mJ. Tuning properties using intracavity CaF2 prism were also investigated and tuning range ~ 4 - 5 μm was observed for both crystals.

Ytterbium doped sodium phosphotellurite glasses are made with different Yb 3+ concentrations. Physical properties of the new glasses are reported. The glasses show high absorption and emission cross-sections and higher lifetime of [equation] transition. Laser performance parameter σ e × τ f , with a value as high as 2.14×10 -20 cm 2 -ms and the laser threshold intensity as low as 1.79 KW/cm 2 are reported. The laser parameters of these Yb 3+ doped glasses show that they are potential to fabricate high power laser and broadband optical amplifiers.

In this contribution, microscopic simulation of optical gain in GaN-based short-wavelength lasers is presented. The model is used to perform a design study of different active regions, and to discuss the impact of inhomogeneous broadening, carrier-induced screening of the piezo charges, and well thickness on material gain and laser threshold current. As a reference, the model parameters are calibrated with temperature dependent Hakki-Paoli measurements of spectral gain. Excellent agreement between measurement and simulation is achieved, which gives the design studies a quantitative character.

We present an experimental study of a Vertical-Cavity Surface-Emitting laser with polarized optical feedback. The system displays single-mode Low Frequency Fluctuations (LFF) for a wide range of pump current. Above the solitary laser threshold we observe a new kind of couple-mode dynamics with a leading LFF behavior in one polarization and an induced pulsed emission in the orthogonal one.

An indication of the level of uncertainty in laser injury studies relates to the slope of the transformed dose-response curve, or the "probit plot" of the data. The most cited threshold in a laser injury experiment is the point on the probit plot that represents a 50 % probability of injury: the ED-50. This value is frequently referred to as the "threshold," even though some experimental damage points exist below this "threshold." An analysis of any number of example data sets reveals that the slope in most experiments could not be explained by biological variation alone. The optical, thermophysical and biological factors influencing the probit plot are critically analyzed. By theoretically modelling an experiment, small errors in focus are shown to produce a substantial change in the ED-50 and the slope of the probit plot. The implications of plotting spot-size dependence with ED-50 values are shown to be significant, and can lead to erroneous conclusions regarding the apparent spot-size dependence.

The faulty microstructure of KDP samples having different bulk laser damage threshold (4 multiplied by 1010 W/cm2 - 5.4 multiplied by 1011 W/cm2 was studied using the methods of the three-crystal x-ray diffraction and two-crystal topography on reflection. A correlation between the dispersion of the structure-sensitive parameters characterizing the microfaultness and the value of bulk laser threshold of samples cut off large KDP crystals was established.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Threshold measurements at 90 femtoseconds (fs) and 600 fs have been made for minimum visible lesions (MVLs) using Dutch Belted rabbit and Rhesus monkey eyes. Laser induced breakdown (LIB) thresholds on biological materials including vitreous, normal saline, tap water, and ultrapure water are reported along with irradiance calculations utilizing nonlinear transmission properties including self-focusing. At both pulsewidths the ED50 dose required for the Rhesus monkey eye was less than half the value determined for the Dutch Belted rabbit eye, all thresholds being 1 microjoule ((mu) J) or less. Measurements on the Rhesus eye at 600 fs found the ED50 dose (0.26 (mu) J) to be much lower than the ED50 dose at 90 fs (0.43 (mu) J). But for these two pulsewidths, almost the same energy level was determined for the Dutch Belted rabbit eye (0.94 (mu) J vs. 1.0 (mu) J). LIB threshold measurements at 100 fs and 300 fs using a simulated eye with isolated vitreous found the ED50 dosages to be 3.5 and 6.0 (mu) J respectively. We found in all cases that the ED50 dosages required to produce MVLs in 24 hours for rabbit and monkey eyes were less than the ED50 values measured for LIB in vitreous or saline or any other breakdown values reported. Also observed was the fact that many of the threshold lesions did not appear in the 1-hour postexposure check but clearly showed up at the 24-hour reading which provided for a much lower threshold dose after 24 hours. We discuss the energy levels and peak powers at which nonlinear effects can begin to occur.

The influence of the atomic lifetime and Raman field strength on the gain and laser threshold in noninverted atomic systems is studied. Results show that to achieve useful gain in such a system, it is necessary to use a sufficiently intense Raman field, atoms with a long lifetime for the lower active levels, and a small cavity loss.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A linear decrease in the 'second laser threshold' is found when two lasers are optically coupled in the bad cavity limit. The coupled lasers are modeled as on-resonance, single mode, homogeneously broadened lasers. In-phase coupling does not cause lasers operating in the good cavity limit to operate chaotically and may make such lasers more stable. The authors observed that out-of-phase coupling of lasers in the good cavity limit can lead to self-pulsing and limit cycles.