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Continuous-wave (CW) lasing is still difficult to realize in organic laser dyes, one reason being the thermal degradation caused by intense photoexcitation. A decrease in laser threshold suppresses...

The molecule N,N′-bis(3-methylphenyl)-N,N′-dyphenylbenzidine (TPD) has been widely used in optoelectronic applications, mainly for its hole-transporting properties, but also for its capability to emit blue light and amplified spontaneous emission, which is important for the development of organic lasers. Here, we report deep-blue-emitting distributed feedback (DFB) lasers based on TPD dispersed in polystyrene (PS), as active media, and dichromated gelatin layers with holographically engraved relief gratings, as laser resonators. The effect of the device architecture (with the resonator located below or on top of the active layer) is investigated with a dye (TPD) that can be doped into PS at higher rates (up to 60 wt%), than with previously used dyes (&lt, 5 wt%). This has enabled changing the index contrast between film and resonator, which has an important effect on the laser performance. With regards to thresholds, both architectures behave similarly for TPD concentrations above 20 wt%, while for lower concentrations, top-layer resonator devices show lower values (around half). Remarkably, the operational durability of top-layer resonator devices is larger (in a factor of around 2), independently of the TPD concentration. This is a consequence of the protection offered by the resonator against dye photo-oxidation when the device is illuminated with pulsed UV light.

A kind of whispering-gallery-mode (WGM) microcavities has been fabricated by melting a corroded erbium-doped fiber with a fiber-fusion splicer. The quality factor (Q) value of the microcavity can reach as high as $3\times 10^{7}$ . The microcavity is pumped by a wavelength-tunable laser source, and due to the high-Q characteristics, the laser threshold can be as low as 21.2 $\mu \text{W}$ in a 60- $\mu \text{m}$ -diameter microsphere-like cavity. By tuning the frequency of the pump laser at 1485 nm with 19.6 GHz, we can tune the WGM microcavity laser by 17.3 GHz around 1578.25 nm.

We report on the mid-infrared laser operation of a cubic 15 at.% E r 3 + : K Y 3 F 10 crystal. In the quasi-continuous-wave regime, the peak power reaches 255 mW at 2.80 µm (the 4 I 11 / 2 → 4 I 13 / 2 transition) with a slope efficiency of 10.9% and a laser threshold of 58 mW. Two pumping schemes (to the 4 I 11 / 2 and 4 I 9 / 2 states) are compared. The emission properties of the E r 3 + ions in K Y 3 F 10 are studied, indicating high stimulated-emission cross-section of 0.57 × 10 − 20 c m 2 at 2.80 µm, a large gain bandwidth of 40 nm, and a long 4 I 11 / 2 state lifetime of 4.64 ms.

We report the results of an experimental study of an ytterbium-doped fiber laser with low Q-factor cavity. We demonstrate that the laser operates in two randomly alternating sub-regimes, quasi-CW (QCW) and self-Q-switching (SQS), the latter ignited by stimulated Brillouin scattering (SBS). We show that probability of each sub-regime depends on pump power: QCW dominates slightly above the laser threshold while SQS pulsing prevails at higher pump powers. We also discuss the featuring details of QCW sub-regime and its role in instabilities (jittering) of SBS-boosted SQS pulsing as well as the statistical properties of the latter.

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.

We demonstrated a low-threshold continuous-wave Raman silicon laser using a high-quality-factor silicon racetrack resonator. The laser threshold was 0.4 mW with a 25 V reverse bias. Lasing without external bias was also observed.

A study of the well-width impact on the AlGaN laser is presented. The laser threshold and optical gain are significantly influenced by the quantum well design. A low threshold of 5 kw/cm2 is achieved in the 3 nm well width due to a reduced QCSE.

Spontaneous photon bursts are observed in the output collected from a mesoscale semiconductor-based laser near the lasing threshold. Their appearence is compared to predictions obtained from Laser Rate Equations and from a Stochastic Laser Simulator. While the latter is capable of predicting the observed large photon bursts, the photon numbers computed by the former produces a noisy trace well below the experimentally detectable limit. We explain the discrepancy between the two approaches on the basis of an incorrect accounting of the onset of stimulated emission by the Rate Equations, which instead are capable of complementing the physical description through topological considerations., 12 pages, 7 figures, 76 references

In this study, high-order distributed-feedback (DFB) polymer lasers were comparatively investigated. Their performance relies on multiple lasing directions and their advantages include their high manufacturing tolerances due to the large grating periods. Nine laser cavities were fabricated by spin-coating the gain polymer films onto a grating structure, which was manufactured via interference lithography that operated at the 2nd, 3rd, and 4th DFB orders. Low threshold lasing and high slope efficiency were achieved in high-order DFB polymer lasers due to the large grating groove depth and the large gain layer thickness. A high-order DFB configuration shows possible advantages, including the ability to control the lasing direction and to achieve multiple-wavelength lasers. Furthermore, our investigation demonstrates that the increase in threshold and decrease in slope efficiency with an increase in the feedback order can be limited by controlling the structural parameters.

We report on a watt-level highly efficient europium laser operating at the 5 D 0 → 7 F 4 transition. It is based on the stoichiometric K E u ( W O 4 ) 2 crystal. Under pumping by a green laser at 532.1 nm, the K E u ( W O 4 ) 2 laser generated a maximum peak output power of 1.11 W at ∼ 703 n m with a slope efficiency of 43.2% and a linear polarization ( E ‖ N m ). A laser threshold as low as 64 mW was achieved. True continuous-wave operation was demonstrated. The polarized emission properties of monoclinic K E u ( W O 4 ) 2 were determined.

Enhancement in rotation sensitivity is achieved in a parity–time-symmetric gyroscope consisting of a ring with gain coupled to a lossy ring, operated below laser threshold and in the vicinity of its exceptional point (EP). An external laser and a conventional readout system are used to measure the large rotation-induced shifts in resonance frequency known to occur in this device. A complete model of the rotation sensitivity is derived that accounts for gain saturation caused by the large circulating power. Compared to a single-ring gyro, the sensitivity is enhanced by a factor of ∼ 300 when the inter-ring coupling is tuned to its EP value κ EP , and ∼ 2400 when it is decreased from κ EP , even though the Sagnac frequency shift is then much smaller. ∼ 40 % of this 2400-fold enhancement is assigned to a new sensing mechanism where rotation alters the gain saturation. These results show that this compact gyro has a far greater sensitivity than a conventional ring gyro, and that this improvement arises mostly from the gain compensating the loss, as opposed to the enhanced Sagnac frequency shift from the EP. This gyro is also shown to be much more stable against gain fluctuations than a single-ring gyro with gain.

Random lasers hold the potential for cheap and coherent light sources, however, improvements in terms of efficiency and laser threshold are required. In this paper, we show two new strategies to increase efficiency and decrease the laser threshold.

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.

DOI: 10.1364/OME.7.000844 URL: https://www.osapublishing.org/ome/abstract.cfm?uri=ome-7-3-844 Filiació URV: SI Memòria We report on a detailed comparative study of the spectroscopic and thermo-optic properties of tetragonal Tm:LiLnF4 (Ln = Y, Gd, and Lu) crystals indicating their suitability for highly-efficient microchip lasers diode-pumped at ~791 nm and operating at ~1.91 ¿m. An a-cut 8 at.% Tm:LiYF4 micro-laser generated 3.1 W of linearly polarized output at 1904 nm with a slope efficiency of ¿ = 72% and a laser threshold of only 0.24 W. The internal loss for this crystal is as low as 0.0011 cm-1. For 8 at.% Tm:LiGdF4 and 12 at.% Tm:LiLuF4 lasers, the output power reached ~2 W and ¿ was 65% and 52%, respectively. The thermal lens in all Tm:LiLnF4 crystals is weak, positive and low-astigmatic. The potential for the Tm:LiLnF4 lasers to operate beyond ~2 ¿m due to a vibronic coupling has been proved. The Tm:LiYF4 vibronic laser generated 375 mW at 2026-2044 nm with ¿ = 31%. The Tm:LiLnF4 crystals are very promising for passively Q-switched microchip lasers.

The influence of the polarization field on the emission properties of the AlGaN-based quantum structures grown on AlN substrates was investigated as a function of well width, barrier width, and barrier height. A thin AlGaN well and a thin AlN barrier design reduced the polarization field to ∼0.5 MV/cm, resulting in an ultralow laser threshold of 3 kW/cm2 in an optically pumped configuration. These experimental results were used to validate the simulation. In the next step, a structure with Al0.7Ga0.3N barriers was designed to support carrier injection with a minimal loss in optical performance. This structure showed a threshold of 7 kW/cm2 under optical pumping and an estimated threshold current of 8 kA/cm2 for the electric injection.

This paper provides a review of advances in conjugated polymer lasers. High photoluminescence efficiencies and large stimulated emission cross-sections coupled with wavelength tunability and low-cost manufacturing processes make conjugated polymers ideal laser gain materials. In recent years, conjugated polymer lasers have become an attractive research direction in the field of organic lasers and numerous breakthroughs based on conjugated polymer lasers have been made in the last decade. This paper summarizes the recent progress of the subject of laser processes employing conjugated polymers, with a focus on the photoluminescence principle and excitation radiation mechanism of conjugated polymers. Furthermore, the effect of conjugated polymer structures on the laser threshold is discussed. The most common polymer laser materials are also introduced in detail. Apart from photo-pumped conjugated polymer lasers, a direction for the future development of electro-pumped conjugated polymer lasers is proposed.

Active laser arrays, of arbitrary pattern, were created by inkjet deposition of self-assembled photonic structures in the form of dye-doped chiral nematic liquid crystals. The print process itself achieves the requisite alignment for photonic band-edge lasing action normal to the substrate; laser threshold and linewidth characteristics are presented.

High quality La 2 CaB 10 O 19 single crystals doped with Pr 3+ ions were grown by means of the top seeded solution growth method. The concentration of Pr 3+ ions in the starting melt was equal to 4 at%, which, due to small distribution coefficient, in consequence gave single crystals containing 2.5 at% of Pr 3+ ions. The piezoelectric coefficients were measured for the pure and Pr +3 doped crystals. The principal changes under influence of the nanosecond pulsed 1064 nm Nd:YAG laser were observed for the LCBO nanocrystallites incorporated into the polymer matrices. The introduction of the Pr 3+ ions favors enhanced piezoelectric constants. In turn the nanocrystallites with enhanced piezoelectricity lead to the enhanced laser threshold damage.

The role of temperature on the properties of quantum-cascade laser (QCL) waveguides is investigated. One-dimensional waveguide parameters are obtained using a transfer-matrix technique and the complex dielectric constants of the waveguide layers are calculated using a semi-classical Drude---Lorentz model. To model the effect of temperature on the waveguide parameters, a temperature dependent electron mobility is incorporated within the Drude---Lorentz framework. It is shown that by including the effect of temperature, a significant improvement in the agreement with experiment of the waveguide loss and hence the laser threshold current density can be achieved.

CW mirrorless laser operation at 1840 nm at room temperature was observed in buried rib waveguides of KY0.58Gd0.22Lu0.17Tm0.03(WO4)2 fabricated by structuring KY(WO4) substrates by Ar-ion milling and subsequent liquid phase epitaxial growth of the active layer on these substrates. Laser efficiency and laser threshold seems to change with the width of the channels fabricated.

Optically pumped lasing from AlGaN/AlN multiple quantum wells grown on single-crystalline AlN substrates with lasing thresholds as low as 6 kW/cm2 is demonstrated via the reduction of unintentional point defects in the active region and waveguide, which reduces the non-radiative recombination by 2 orders of magnitude. A higher lasing threshold of 11 kW/cm2 is observed for AlGaN barriers, owing to the reduced localization of electrons and holes in the wells. It is shown that for electrically injected UVC laser diodes, AlGaN barriers are essential.

The laser was born on May 16, 1960 at Hughes Research Laboratories in Malibu, California. Instead of enjoying the view of the Pacific from his new office window, Theodore Maiman closeted himself in a windowless lab, where he slipped a spring-shaped photographic flashlamp over a stubby ruby rod, then put the assembly inside a reflective cylinder. Firing pulses with higher and higher voltage through the lamp, he carefully studied oscilloscope traces of the rise and fall of the ruby's red fluorescence. Once the voltage exceeded 950 volts, the lamp flashed bright enough to excite the ruby above laser threshold. The red light suddenly flashed so bright that Maiman's colorblind assistant Irnee D'Haenens saw red light for the first time [1]! The instruments recorded what Maiman had predicted would happen above laser threshold – the pulse rose and fell faster, and the range of red wavelengths narrowed. This article provides an overview of the first 50 years of laser development as well as a brief outlook what's coming next.

A kind of Faraday glass with a size of Φ40 mm × 14 mm and Φ100–300 mm × 25 mm, respectively, was prepared by the melting and casting process, which had neither a Pt particulate nor a bubble or striation. The measurement results showed that the surface homogeneity of the samples was up to ± 1 × 10−6, the laser threshold reached 10 J/cm2 (1ω, 3 ns), and the Verdet constants of the glasses were −0.273 min/Oe/cm at 632.8 nm and −0.076 min/Oe/cm at 1064 nm, respectively.

The microcavity and the influence of nonradiative recombination can control spontaneous emission. An analytic resolution of rate equation is studied for microcavity lasers. The relationship between output properties and structural parameters of multi-quantum wells (MQWs) is obtained. One of the most important consequences of the increased spontaneous emission factor is the reduction of laser threshold. It is found that the characteristic curve of a "thresholdless" laser is strongly nonradiative depopulation-dependent. The light output is increased by the enhanced well number and the reduced width. In particular, there is an optimal well number corresponding to the lowest threshold current density for MQW structure in the microcavity lasers.

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.

The threshold properties of photonic crystal quantum dot lasers operating in the slow-light regime are investigated experimentally and theoretically. Measurements show that, in contrast to conventional lasers, the threshold gain attains a minimum value for a specific cavity length. The experimental results are explained by an analytical theory for the laser threshold that takes into account the effects of slow-light and random disorder due to unavoidable fabrication imperfections. Longer lasers are found to operate deeper into the slow-light region, leading to a trade-off between slow-light induced reduction of the mirror loss and slow-light enhancement of disorder-induced losses., 5 pages, 7 figures

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.

Cd(Zn)Se/ZnSe green (λ = 510–530 nm) lasers have been investigated in wide temperature and power ranges under pulsed optical excitation. The minimum laser threshold, maximum external quantum efficiency and maximum output power have been found to be 10 kW/cm2, 12%, and 20 W, respectively, in heterostructures with multiple CdSe quantum disc sheets in an active region. The high temperature stability of threshold power densities (T0 = 330 K up to 100 °C) has been observed. For the optical excitation of the green lasers, optically-pumped InGaN/GaN quantum well heterostructures grown on Si (111) substrates has been used for the first time. The conversion coefficient of energy is about 0.01. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The absorption spectra of Tb,Tm:YVO4 and Ho,Tm:YVO4 are measured. The radiant and non-radiant transition probabilities from higher level to lower level, Ai,j and ?i,j and the cross-relaxation probability are calculated in virtue of Judd?Ofelt and Dexter theories. The fluorescence lifetime of Tm3+ in the Tb3+ (or Ho3+) co-doped crystal is calculated. It indicates that the lifetime of initial level 3H4 of the laser transition can be shorter than that of terminal level 3F4 of the transition if the atomic percentage of Tb3+ (or Ho3+) ions is bigger than about 1 at%: namely, by means of the co-doping Tb3+ (or Ho3+) ions the self-termination phenomenon of laser light can be eliminated. Inserting the optic parameters to the formula deduced here on the laser threshold power P(4)th and the slope efficiency ?(4)s of the four-energy-level system, we obtain the relationship of threshold power P(4)th to the concentration of Tm3+ ions and discuss the effect of Tb3+ (or Ho3+) ion concentration on the laser threshold power P(4)th around 1.5?m wavelength. The result shows that Tb,Tm:YVO4 crystal is a better choice to make the laser at ~1.5?m wavelength than Ho,Tm:YVO4 crystal. We give the appropriate composition of (1?2) at% Tb, (1?2) at% Tm:YVO4, just for reference.

The dependence of the refractive index and emission line-width of laser crystals on the atomic parameters of ions in the crystals has been analyzed qualitatively. As a result, an empirical relationship between laser threshold and chemical composition of laser crystals is proposed and demonstrated by some oxide crystals. The relation may be useful for the investigations of laser crystals.

We study theoretically the non linear polarization dynamics of Vertical-Cavity Surface-Emitting Lasers in the presence of an external cavity providing delayed optical feedback and cross polarization re-injection. We show that far from the laser threshold, the dynamics remains confined close to the equatorial plane of a Stokes sphere of a given radius and we reduce the dynamics to a dynamical system composed of two phases: the orientation phase of the quasi-linear polarization and the optical phase of the field. We explore the complex modal structure given by the double feedback configuration and recovers as particular cases the Lang-Kobayashi modes and the modes founds by Giudici et al. [1]. We also re-interpret the square waves switching dynamics as phase kinks.

We compare orientational relaxation phenomena of a light-emitting polymer and a, spectroscopically similar, conventional laser dye in solutions of comparable viscosity. The orientational relaxation time of the laser dye is found to be very much smaller than that of the polymer. This result is attributed to the large difference in shape between the two light-emitting materials. We demonstrate that these very different reorientation times have a major influence on the operation of a gain-switched laser based on these gain media, in particular on its threshold.

This paper reports the thermal properties and 1·064 m m lasing characteristics of Nd3+:LaVO4 crystal pumped with a Ti:sapphire laser. The maximum laser output power is 107 mW at the pumping power of 461 mW. The slope and light conversion efficiency are 52·8 and 22·9% respectively, and the laser threshold is 45 mW. These results indicate that Nd3+:LaVO4 crystal can be regarded as a new laser crystal.

Energy-transfer processes have been quantitatively studied in various Tm:Yb-doped fluoride crystals. A comparison between the three host crystals which have been examined $({\mathrm{KY}}_{3}{\mathrm{F}}_{10},$ ${\mathrm{LiYF}}_{4},$ and ${\mathrm{BaY}}_{2}{\mathrm{F}}_{8})$ shows clearly that the efficiency of the $\mathrm{Y}\stackrel{\ensuremath{\rightarrow}}{b}\mathrm{Tm}$ energy transfers is larger in ${\mathrm{KY}}_{3}{\mathrm{F}}_{10}$ than in ${\mathrm{LiYF}}_{4}$ or ${\mathrm{BaY}}_{2}{\mathrm{F}}_{8}.$ The dependence of the energy-transfer parameters upon the codopant concentrations has been experimentally measured and compared with the results calculated on the basis of migration-assisted energy-transfer models. Using these energy-transfer parameters and a rate equation model, we have performed a theoretical calculation of the laser thresholds for the ${}^{3}{\stackrel{\ensuremath{\rightarrow}}{{H}_{4}}}^{3}{F}_{4}$ and ${}^{3}{\stackrel{\ensuremath{\rightarrow}}{{H}_{4}}}^{3}{H}_{5}$ laser transitions of the Tm ion around 1.5 and 2.3 \ensuremath{\mu}m, respectively. Laser experiments performed at 1.5 \ensuremath{\mu}m in ${\mathrm{Y}\mathrm{b}:\mathrm{T}\mathrm{m}:\mathrm{L}\mathrm{i}\mathrm{Y}\mathrm{F}}_{4}$ then led to laser threshold values in good agreement with those derived theoretically. Based on these results, optimized values for the Yb and Tm dopant concentrations for typical values of laser cavity and pump modes were finally derived to minimize the threshold pump powers for the laser transitions around 1.5 and 2.3 \ensuremath{\mu}m.

LuLiF4 single crystals codoped with thulium (Tm) and holmium (Ho) were successfully grown by the Czochralski method. The excellent laser performance, in terms of highest slope efficiency, and highest optical-to-optical efficiency and lower laser threshold, was studied in comparison with 5% Tm, 0.5% Ho-codoped YLiF4, and Lu3Al5O12 under the same conditions.

The dynamics of the laser model based on the nonlinear coupling of light-field with boson elementary excitation is improved. A rate equation of pumping system directly coupled with the boson matter is added to the original equations. The system as a whole, therefore, becomes a perfect self-organized one, but the character of mirrorless unchanges, which is a character essentially different from conventional lasers, and the laser threshold behavior of second-order-like transition also remains. There is some resemblance between the new revised laser model and Maxwell–Bloch two-level-atom laser model.

When AIGalnAs laser structures are grown by molecular beam epitaxy on InP, the substrate deoxidation procedure is found to influence the quality of the structure: the laser threshold current densities are found to be low and reproducible when P2 is used for the substrate deoxidation. On the other hand, the reproducibility is not achieved with a deoxidation under As2. In order to interpret this result, very thin AlInAs overlayers have been deposited on InP substrates which were preliminarily deoxidized under P2 or As2 flux. The AlInAs morphology is observed by atomic force microscopy. The InP anneal under As2 leads to a rough surface as compared to the InP anneal under P2. These observations suggest that a systematic use of P2 for the substrate deoxidation can definitely improve the reliability of AIGalnAs laser structures on InP.

Nd:YLF laser at 908 nm, providing an QCW output power of 6.4 W at 33 W of absorbed pump power and a laser threshold of 3.2 W of absorbed pump power at 797 nm.

We demonstrate optically pumped lasers with active layers of indirect-gap Al\(_{\rm x}\)Ga\(_{1-{\rm x}}\)As operating up to room temperature. The emission wavelength is 609 nm at 20 K and 639 nm at 300 K, respectively. The laser threshold shows a weak sensitivity on the lattice temperature. The relevant parameters of the lectron-hole plasma close to threshold are determined from gain spectroscopy using the variable stripe-length method.

This review summarizes recent developments and successes in the theoretical modelling of the characteristics of semiconductor microcavity lasers. After a discussion of the basic laser properties, results of a quasi-equilibrium many-body theory are presented which are very useful for the understanding of microcavity laser operation not too far above the laser threshold. Non-equilibrium phenomena, such as spectral and kinetic hole burning as well as plasma heating effects, are analysed using a quantum kinetic approach. Comparisons with experimental observations are discussed, before open problems and future challenges are outlined.

Laser power and energy have been measured for the transitions at 1.73 and 2.03 /spl mu/m in atomic xenon, and 1.27 and 1.79 /spl mu/m in atomic argon, for gas temperatures between 290-585 K. Nuclear excitation using /sup 235/U fission-fragments provided pump powers between 2-10 W/cm/sup 3/. Peak laser output in xenon was independent of gas temperature below 400 K. Laser output at 1.79 /spl mu/m in argon decreased monotonically with increasing gas temperature while the 1.27 /spl mu/m laser output was independent of gas temperature below 380 K. In all cases, the laser threshold increased as the gas temperature increased. >

A scaling law obeyed by photon number fluctuations near threshold in the Ginzberg-Landau theory of second order phase transition is described. Normalized factorial moments are found to scale as F r ∼ F β r 2 , r ⩾ 3. The results from photon counting experiments on laser fluctuations near threshold are shown to support this scaling law. It is found that β r = ( r − 1) v , where v = 1.304. Implication of the scaling behavior is discussed.

We report for the first time on the observation of self-mode-locking in a diode pumped self-Q-switched (SQS) Nd3+,Cr4+:YAG laser. This phenomenon results from significant excited state absorption of the Cr4+ ions in the co-doped host during the SQS laser pulses. The self-mode-locking occurs already slightly above the SQS laser threshold. Experiments using relatively low saturable intensity achieved a modulation depth of more than 40%.

The results of local laser simulation for estimation of SEE parameters are presented. Simulation method is based on the local laser irradiation of VLSI by measuring response in power supply circuits and determining laser threshold energy of SEE.

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.

The authors examine the power efficiency of the fission-fragment-excited atomic argon laser operating on the 1.27- mu m (3d'(3/2)/sub 1/-4'/sub p/(3/2)/sub 1/) argon transition as a function of pump power, gas mixture, and pressure. The maximum measured power efficiency was 1.1+or-0.3% for a gas pressure of 1300 torr and a He/Ar ratio of 99.88/0.12. Neon addition to the He/Ar gas mixture increased both the energy deposited in the gas and the energy output without decreasing efficiency for a neon gas fraction of less than 0.5. Small-signal gain and saturation intensity are between 0.15-0.27%/cm and 25-200 W/cm/sup 2/ for pump rates of 7.5-30 W/cm/sup 3/ in He/Ar and He/Ne/Ar gas mixtures. The laser threshold as a function of total pressure and argon concentration is presented. >

Antiresonant reflecting optical waveguide (ARROW-type) vertical-cavity surface-emitting lasers are designed for high-power single-mode operation. A detailed full-vector finite-difference time-domain (FDTD) study shows strong modal discrimination in favor of the fundamental mode for large aperture (>6 /spl mu/m), large index-step (/spl Delta/n>0.025) simplified ARROW-type devices. The FDTD model identifies the polarization-dependent radiation losses of the higher order modes, which prevent them from reaching laser threshold.

The increase in slope efficiency and the reduction of the laser threshold of a flash-lamp-pumped Ho,Cr,Tm:YAG laser that are due to increased flash-lamp efficiency when the current of the dc simmer is increased are described. Investigations of the electrical characteristics of the flash lamp as a function of the simmer current prove that the flash-lamp impedance decreases to a constant value when the dc simmer current is increased. As a consequence an increase of the peak current through the flash lamp is observed, which improves the flash-lamp efficiency.