Spectral, luminescent, photochemical, and laser properties of a series of boron fluoride complexes of dipyrrolylmethenes in solutions

We have studied the spectroscopic and lasing characteristics of active media based on two synthesized boron fluoride complexes of alkyl-substituted dipyrrolylmethenes and the photostability of the complexes in comparison with complexes of this kind that were previously studied in the literature under identical excitation conditions. We have determined and analyzed conditions under which new compounds have either merits or drawbacks as compared to the known dye with respect to both lasing efficiency and resource characteristics.     

Spectroscopic and Laser Studies of Mixed Rhodamine 6G and 10-Phenyl-9-acetoxyanthracene Solutions

The spectroscopic and laser parameters of a mixed donor (10-phenyl-9-acetoxyanthracene derivations)-acceptor (rhodamine 6G) solutions have been determined. The studies performed show that rhodamine 6G is responsible for the lasting of the mixed solution. The 10-phenyl-9-acetoxyanthracene added to the R6G lasing solution decreases the spectral range of lasing and the gain value, G(), of the solution. These changes in the lasing parameters are caused by electron energy transfer processes of different types. The results of fluorescence studies of the mixed donor-acceptor solutions point out that the long-range dipole-dipole interaction mechanism of the static quenching accompanied by the formation of nonemitting complexes in the dye mixture is responsible for the noted lasing and fluorescence changes.     

Spectroscopic and laser characteristics of new efficient luminophores for a wide spectral range based on complexes of dipyrrolylmethene derivatives with difluorine borate

We have studied the spectral-luminescent, lasing, photochemical, and endurance characteristics of a series of new efficiently emitting difluorine borate complexes with dipyrrolylmethenes of different structures. Experimental data have been obtained in polar and nonpolar organic solvents and in solid polymer films involving the participation of silicate structures. We have discussed relations of the structure of investigated compounds and formed solvates with their optical characteristics, and have given guidelines on the use of particular compounds as active media of tunable lasers for determining spectral ranges.     

Injection seeding of lasing in microdroplets

Injection seeding of lasing has been achieved in both small (~20-mu; m radius) and larger (~35-mu; m radius) dye-doped microdroplets. Seeding is effective in enhancing the intensity from one lasing mode that normally occurs because of the droplet morphology. Competition between the seeded mode and unseeded lasing modes that have good spatial overlap with the seeded mode prevents lasing on some unseeded lasing modes.     

轴向隐失波激励的回音壁模式光纤激光器

采用轴向隐失波激励增益的方式,使激光增益区域局限在光纤回音壁模式的模场区域内,显著地降低了回音壁模式光纤激光辐射的抽运阈值,由此形成一种低阈值的回音壁模式光纤激光器.在微焦耳量级的低抽运能量条件下,用回音壁模式光纤激光器研究了激光染料的浓度效应.实验结果表明,随着激光染料浓度的增加,回音壁模式激光辐射的波长向长波方向移动,激光波长范围变宽.用回音壁模式染料激光的四能级模型得到激光上能级和所有能级上的分子数比值γ(λ)曲线后,很好地解释了实验结果.低抽运阈值的回音壁模式光纤激光器,为研究液体激光现象提供了极为便利的手段.     

Stable biexcitonic lasing of CuCl quantum dots under two-photon resonant excitation

We have observed ultraviolet lasing of CuCl quantum dots embedded in a NaCl single crystalline matrix. Stable ultraviolet lasing of biexciton (two e–h pairs) luminescence has been achieved below 70 K under the two-photon direct excitation of biexcitons of CuCl quantum dots. Laser action occurs with parallely cleaved surfaces of the NaCl crystalline matrix acting as an optical cavity, which shows a very high efficiency of lasing.     

Multiwavelength erbium-doped fiber ring lasers with overlap-written fiber Bragg gratings

Eight-wavelength Er-doped fiber lasers with lasing wavelength separations of ~1.6 and ~0.8 nm , respectively, have been achieved by use of overlap-written fiber Bragg gratings (OWFBG's) in the fiber lasers and by cooling of the Er-doped fiber with liquid N(2) . Our experiment shows that by utilizing the OWFBG's to select the lasing wavelengths one can achieve fiber lasers with lasing wavelengths and lasing wavelength separations that match the International Telecommunication Union channel-allocation grid well.     

Self-detection of lasing characteristics for semiconductor ring laser diodes

A novel method of measurement of lasing characteristics for a ring laser diode is proposed without branching of the optical lasing power. The lasing power and the linewidth as a function of the injection current have been measured by detecting the RF power by the terminal voltage change of a ring LD. The linewidth is estimated to be 55 kHz atl=1.75l _th.     

掺Yb光纤激光器激射波长与阈值关系研究

依据石英中 Yb3 的能级和光谱特性 ,推导了掺 Yb光纤激光器中激射波长与抽运阈值等的关系式。依据所得到的关系式 ,深入分析、研究了抽运功率、损耗及阈值对激光运行波长的影响。进行了相关实验 ,理论与实验结果符合得很好     

Effects of phase fluctuation in an open four-level inversionless lasing system

A steady analytical solution of an open four-level inversionless lasing system with a driving field having the phase fluctuation has been given, and the effects of the finite width due to the phase fluctuation on the gain, dispersion, and population difference have been analyzed by using the numerical simulation from the steady analytical solution. It is found that: with the linewidth increasing, the gain decreases and the absolute value of population difference between levels coupled by the probe field increases, but the variation of the linewidth cannot change the properties of the inversionless lasing and refractive index increase of the system; when the linewidth does not equal to zero, the system can still get a high refractive index with zero absorption, and these conclusions have very obvious difference from those obtained in other inversionless lasing systems.     

Determination of the stimulated raman scattering threshold for a pump pulse of arbitrary width

The spectral luminescent, photophysical, photochemical, lasing, nonlinear optical, and sensor characteristics of a series of new synthesized complexes of zinc and difluoroborate with dipyrrines of different structure have been studied. It is found that many of these compounds exhibit stimulated emission in different solvents when excited by the second (532 nm) and third (355 nm) harmonics of a Nd:YAG laser in the range of 548–692 nm. It is shown that not only efficient fluorophores belonging to dipyrrine difluoroborates (with a quantum fluorescence yield close to 1), but also compounds with a fluorescence yield equal to 0.3, generate laser radiation with a high resource; phosphorescence is also observed along with fluorescence. Transmission of UV radiation (355 nm) is shown to decrease with an increase in the pulsed excitation power density; this is a manifestation of nonlinear optical properties. The change of phosphorescence signal in dependence of the composition of the gas mixture around a solid-state sample colored by dipyrrinate complexes indicates that a number of the compounds under consideration exhibit sensor abilities.     

Laser dye stability

The experimental parameters for solution temperature, solvent purity, and ultraviolet (uv) light removal have been examined as they affect the first-order bleaching constant, lasing slope efficiency, lasing threshold, and laser half-life of three dyes using air as the cover gas. A±10°C change from the ambient temperature was found to reduce the lasing output of solutions of the dyes rhodamine 6G, LD-490, and coumarin 102. Improving the purity of the solvent made no dramatic effects but did tend to yield somewhat lower bleaching rates and longer lasing lifetimes. The first-order bleaching constant for the dye LD-490 in several solvents was found to decrease in the order methanol >95% ethanol>ethanol. Although LD-490 in ethanol had twice the laser lifetime of that in methanol, the use of uv light filtration reversed this order. However, LD-490 still bleached faster in methanol than it did in ethanol. Interestingly using the uv filter, germicil quartz, did not decrease the lasing slope efficiency, but it made a slight increase in both the lasing slope efficiency and the lasing threshold. The use of the more strongly absorbing pyrex filter did, however, decrease the lasing slope efficiency as well as increase the threshold.     

光纤回音壁模式激光产生长度的实验与理论研究

采用沿光纤轴向光抽运消逝场激励增益的方式,获得了沿光纤轴向较长范围的回音壁模式激光辐射.研究了这种激光器的激光产生长度与抽运能量间的关系.实验发现:当抽运能量刚超过激光产生阈值时,激光产生长度迅速增长;随抽运能量的继续增加,产生长度的增长趋势变缓;产生长度随抽运能量的变化关系决定于增益包层溶液的染料浓度和溶液折射率.根据抽运光沿光纤轴向以受抑全反射方式传播的物理特性,在抽运能量中引入了遵循比尔吸收定律的指数衰减函数,结合消逝场激励增益的回音壁模式激光理论,在分析系统增益和损耗的基础上由激光阈值条件推导出了 关键词： 回音壁模式 受抑全反射 消逝场 激光产生长度     

Lasing characteristics of a pendant drop deformed by an applied electric field

The lasing properties of an oval-shaped resonant cavity (ORC) with a continuously variable aspect ratio have been studied. The ORC was formed with a dye-doped pendant drop placed inside a variable static electric field. When the drop ORC was pumped by a nitrogen laser, lasing from the ORC was found to have strong directional emission characteristics and an intensity enhancement factor as great as 19.5. Calculated results of light rays escaping from ORC's by refraction are in good agreement with the experimental data.     

Pulsed first-overtone CO laser: effective source of IR radiation in spectral range of 2.5–4.0 μm

Spectral properties of radiation of a pulsed electron-beam controlled discharge laser operating on the first-overtone transitions (Δv=2) of CO molecules have been studied both experimentally and theoretically. Various sets of dielectric mirrors with high reflectivity in the wide range of overtone spectrum have been used for the laser resonator. Multiwavelength lasing has been obtained in the wide spectral range of 2.5–4.0 μm. Efficiency of the laser operating on few vibrational transitions within a relatively narrow spectral range comes up to 5% at entirely suppressed fundamental band (Δv=1) lasing. Spectral characteristics of the overtone laser operating on a selected set of vibrational transitions have been analyzed theoretically. A comparison of the experimental and theoretical data has been made.     

Scattering and amplification of light in a layer of a nematic liquid crystal

The role of light scattering in liquid crystal lasers can be of two kinds. It can induce undesirable losses increasing the lasing threshold or it can promote the appearance of feedback necessary for lasing. The light amplification spectra of the liquid crystal in the isotropic and light-scattering nematic phases have been measured. For comparison, at a close pump power, the amplification spectra have been measured on a TiO₂ nanoparticle suspension in an isotropic solvent, where the mean free path of photons is the same as that in the liquid crystal. The amplifications in two systems are significantly different, because the shapes of their scattering patterns are strongly different.     

Investigation of vibrational relaxation of excimers

The excimer vibtational relaxation have been studied in the diffusional approximation, and stationary substantially non-equilibrium populations of high vibrational levels have been found. New formulae have been derived for quantum yield of UV lasing. Taking into account the vibrational relaxation the new effect of far-IR radiation amplification in the active media of excimer lasers is predicted.     

LASING FROM A DYE-DOPED PENDANT DROP AND ITS PRECESSION

We have observed lasing from the rim of dye-doped ethylene glycol pendant drops. Spatial-resolved spectral measurements show that the lasing wavelength varies along a vertical rim of the drop. Time-resolved measurements indicate that lasing precession occurs within the drop. Various lasing patterns due to lasing precession are explained. The measured precession periods for different pumping points are in good agreement with the calculated values based on morphology-dependent resonance theory.     

Characterization of the 46.9-nm soft X-ray laser beam from a capillary discharge

Intense lasing had been obtained from argon plasma in the soft X-ray region from a capillary discharge plasma system. Different diagnostics have been used to characterize the lasing properties by recording the temporal, spatial, and spectral profiles of the emission. The divergence measurement indicates that the soft X-ray laser beam has good directionality with a divergence of 3.5 mrad. The spectrum of the laser beam measured using a transmission grating showed intense lasing line at 46.9 nm. Diffraction orders as high as 10th orders were observed. The temporal profile recorded with a vacuum diode showed a distinct laser peak with a pulse width ~1.2 ns (FWHM). In addition, the coherence of the X-ray laser beam was also confirmed from the high-contrast interference fringes (visibility ~85 %) recorded using double slits.     

Analysis of various optical pumping schemes for liquid oxygen lasers

Singlet oxygen generated by optical pumping in liquid oxygen/air medium has recently been reported as a potential gain medium for high power lasers at 1580 nm, by USA’s defense agency DARPA. However, the details with reference to the underlying physics of this laser and the potential pumping techniques for achieving lasing are still unclear. The present paper investigates numerically the population kinetics of both upper and lower lasing levels viz. O₂ and O₂ states in liquid oxygen and discusses the criticality involved in obtaining lasing with this medium. Isotopic liquid oxygen and liquid air medium where improved conditions for lasing are anticipated, as compared to that in natural liquid oxygen, have also been considered in the present study. The studies have been carried out for optical pumping by both continuous and pulsed mode lasers at 1064 nm and 634 nm wavelengths. The temporal variation of small signal gain in each case has been investigated along with limitations of the same from point of view of lasing. The available and extractable power from all three medium for an optimum pumping case has also been discussed. The studies reveal that liquid air has high potential for very high power lasers as compared to both natural and isotopic liquid oxygen. PACS 31.15.ag