Laser dye stability

A figure-of-merit (FOM) consisting of the initial laser slope efficiency times the dye lifetime constant is used to compare the effect of a Pyrex light filter and the cover gas upon the output characteristics of six laser dye solutions. The FOM is found to improve using the Pyrex filter from 2-fold (coumarin 102 under air) up to 3800-fold (rhodamine 6 G under argon). In most cases, the use of argon in place of air for a coumarin dye not only improves the laser output, but also increases the lifetime constant. However, two of the coumarin dyes had an increase in lifetime under air as compared to under argon. This difference is explained in terms of the relative energy levels of the singlet and triplet states of these dyes. In order to measure long-lived dye solutions, a separate output-monitored linear flashlamp was used to degrade the solutions. The dye lifetime constants were corrected for changes in the output of this linear flashlamp. The relative output of this dye degradation flashlamp was found to depend upon the wavelength of the measurement and the position of the sensor along the length of the lamp. The variation in the output of several flashlamps is shown for lamps operating up to a total of 30 million flashes. The lifetime constants of the dye LD-490 measured by using the coaxial laser flashlamp was found to be comparable with, but lower than, the constants obtained from using the linear dye-degradation flashlamp.     

Laser dye stability. Part 4

Changes in the absorption of a dye laser solution are examined after excitation with a xenon flashlamp. It is found that the rate of bleaching as a function of the total input energy of coumarin or quinolone dyes in ethanol increases in direct proportion to the dye concentration. This relationship suggests that the dye reacts with a photoproduct of the solvent rather than being directly decomposed by the xenon flash. We have measured the conversion of the dye to form products,P, absorbing at the lasing wavelength. Results correspond to the dye reacting with a precursor ofP to form either insoluble products or ones not absorbing at the lasing wavelength. Thus larger total amounts of bleached dye do not proportionately increaseP, and hence do not proportionately inhibit lasing. Furthermore, we find thatP increases with the total input energy fairly independent of the rate of bleaching for a given bicyclic dye in an alcohol solution.     

Laser dye stability. Part 4

Changes in the absorption of a dye laser solution are examined after excitation with a xenon flashlamp. It is found that the rate of bleaching as a function of the total input energy of coumarin or quinolone dyes in ethanol increases in direct proportion to the dye concentration. This relationship suggests that the dye reacts with a photoproduct of the solvent rather than being directly decomposed by the xenon flash. We have measured the conversion of the dye to form products,P, absorbing at the lasing wavelength. Results correspond to the dye reacting with a precursor ofP to form either insoluble products or ones not absorbing at the lasing wavelength. Thus larger total amounts of bleached dye do not proportionately increaseP, and hence do not proportionately inhibit lasing. Furthermore, we find thatP increases with the total input energy fairly independent of the rate of bleaching for a given bicyclic dye in an alcohol solution.     

Dye laser spectrum narrowing by “double pulse” flashlamp pumping

A novel simple “two-step lasing” technique for flashlamp dye laser spectrum narrowing is proposed. The laser spectrum is locked by double pulse pumping at the preliminary narrowed prepulse emission. Experimental check on the example of waveguide flashlamp pumped dye laser is reported.     

Laser dye stability

Lasing characteristics and bleaching of four Eastman Kodak ir dyes have been examined in dimethyl sulfoxide. These ir dyes are shown to improve in performance in the absence of oxygen. Their photochemical stability was found to be comparable to the quinolone laser dyes when exposed to flashlamp excitation. Photodecomposition of the ir dyes under lasing conditions was found to vary between 1.6 and 6×10⁻¹⁰ moles of dye for each joule (electrical) of input energy; in comparison, the photodecomposition values for the better coumarin dyes was 0.2 to 1.0×10⁻¹⁰ moles/J at a concentration of 1.0×10⁻⁴ M in ethanol. It was also found that increasing the concentration of these tricarbocyanine dyes gives a marked improvement in the useful lifetime of these solutions as lasing media in the absence of oxygen.     

Spectral narrowing in a dye laser with non-resonant feedback

The temporal development of the spectral output of a flashlamp pumped dye laser, having non-resonant feedback achieved by means of fibre optics, has been studied using a streak camera. Spectral narrowing from 40 nm (the bandwidth of the spontaneous fluorescence of the system) to 2.5 nm has been observed, with the degree of spectral narrowing depending upon the output power.     

Laser dye stability part 8

A 3-parameter dye laser degradation equation is introduced that has been based upon a theoretical analysis of a laser oscillator. The new equation and the 4-parameter empirical laser degradation equation used previously in this series are further developed to allow calculation of the lifetime of a dye solution for any fraction of laser output degradation. These lifetime equations are shown to be dependent upon the input energy per pulse and the threshold of lasing. The new 3-parameter equation allows the degradation constants to be determined with less change in laser output than did the original 4-parameter empirical expression.     

Solid-state dye lasers based on polymethyl methacrylate doped with pyrromethene 650

Solid-state dye samples based on polymethyl methacrylate (PMMA) doped with different concentrations of the dye PM650 were prepared. With SHG of Q-switched Nd:YAG laser (532 nm, ∼15 ns) pumping the samples longitudinally, the fluorescence, lasing spectra and slope efficiencies of the samples were obtained. The highest slope efficiency 27.49% and laser output energy 22.0 mJ was achieved in the sample with a dye concentration of 2.0 × 10⁻⁴ mol/L. To our knowledge, the results are the best under the same condition so far. The maxima of output lasing spectrum is about 653.5 nm. Our results have shown that using solid-state samples doped with PM650 can extend the dye laser wavelength to the red.     

Lasing properties of some metal complexes of compounds containing the methyleneiminobisacetic acid group

Aqueous solutions of some fluorescent metal complexes of three compounds containing the methyleneiminobisacetic acid group have been found to show lasing when tested on a pulsed nitrogen laser. Degradation constants for lasing of one of the complexes and of the corresponding uncomplexed dye have been determined by coaxial flashlamp pumping.     

A large coaxial lidar for elastic and inelastic scattering studies of the stratosphere

A very powerful, fixed zenith laser radar system, based upon a liquid dye laser, is described in detail. The laser is a linear flashlamp pumped dye system capable of an average power output of 6W at a prf of 3 s^–1 using rhodamine 6G dye and about 3W with the same prf using esculin monohydrate dye. The use of this laser as a transmitting source in the lidar system has permitted the detection of Stokes shifted vibration/rotation Raman back-scattered light from neutral nitrogen in the stratosphere and from these measurements, stratospheric temperature profiles have been derived. The lidar has also been used to study elastic backscattering from the stratosphere at two wavelengths and preliminary results of a new technique for studying stratospheric aerosol are presented.     

Distributed feedback dye laser holographically induced in improved organic–inorganic photocurable nanocomposites

Distributed feedback (DFB) lasing in permanent volume transmission gratings formed in a laser dye-doped organic–inorganic nanocomposite has been investigated. DFB laser cavities were fabricated using one-step two-beam holographic exposure of Pyrromethene 567 (PM567) doped photopolymerizable acrylate monomers containing inorganic (LaPO₄) nanoparticles. Compared to the formulation previously utilized, the material composition presented provides longer lifetime of the laser. Spectral and polarization properties, input–output and stability characteristics of the laser output have been investigated by varying the material composition and the patterning parameters. DFB lasing emission of the second and the third diffraction orders has been demonstrated. The spectral linewidth of ∼0.08 nm has been observed at a pump energy threshold of about 0.2 μJ/pulse for the second-order DFB lasing when pumped with 532 nm 500 ps laser pulses. Spectral tuning of the lasing output over ∼56 and ∼7 nm was obtained by varying the grating period and the content of inorganic nanoparticles in the polymer matrix, respectively.     

Study of acid-base dye laser systems

Rate equations with temporal, spectral and spatial dependences are derived to obtain the characteristics of the laser emission of dye molecules that undergo acid-base processes. The model has been tested to reproduce the experimental results of the laser emission due to the monoprotonated species of 4-amino-7-phenyl-8H-pyrazino[2,3-c]-1,2,6-thiadiazine 2,2-dioxide in acetonitrile. Numerical solution of the rate equations is performed to predict general lasing characteristics of acid-base dye laser systems. The temporal evolution and the superficial density of output energy of both a neutral and a base species are studied as a function of the pumping energy and the acidity of the solution. Cases of equilibrium or nonequilibrium in the excited state and overlap or nonoverlap between fluorescence and absorption bands of the different species are considered. The possibility of simultaneous lasing of both species at two different frequencies is discussed.     

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.     

Energy transfer in slab dye lasers

A simple model of the energy transfer between a booster dye and the active dye in a flashlamp pumped planar waveguide dye laser is described.Analytical results are compared with experiments for several dyes in the 600–650 nm region.A twofold increase of laser output was found at a wavelength (630 nm) which is of particular interest for several applications.     

非相关双束可调谐染料激光器实验研究

本文报道了研制成功的闪光灯泵浦矩形非相关双束可调谐染料激光器,它可同时在两种染料中获得双束激光输出,具有频差大、脉冲同步、无模式竞争等特点。文中给出了装置结构和典型实验结果,并做了简单讨论。 关键词：     

Dynamic nonlinear effect on lasing in a random medium

We have studied both experimentally and numerically the dynamic effect of nonlinearity on lasing in disordered medium. The third-order nonlinearity not only changes the frequency and size of lasing modes, but also modifies the laser emission intensity and laser pulse width. When the nonlinear response time is longer than the lifetime of the lasing mode, the nonlinearity changes the laser output through modifying the size of the lasing mode. When the nonlinear response is faster than the buildup of the lasing mode, positive nonlinearity always extracts more laser emission from the random medium due to the enhancement of single particle scattering.     

Significance of intra-cavity power density in synchronous mode-locking of CW-dye lasers

It is shown that there is a well-defined relation between the intra-cavity power density and the temporal structure of ultrashort light pulses generated by a synchronously pumped cw dye laser. To obtain pulses of good quality with high output power the beam cross-section in the lasing medium must be large, because the best performance is achieved at low power density.     

Search for efficient,near UV lasing dyes. III. Monocyclic and miscellaneous dyes

A potential new class of “monocyclic” lasing dyes is discussed and four families out of nine within the class are examined. The 2,6-diaminopyridines in acid are found to lase under flashlamp excitation but show low slope efficiencies and lower stabilities than the “bicyclic” dyes described previously. Other, miscellaneous dyes show oxygen quenching of laser action rather than enhancement and the best of these produces short pulses under long pulse excitation. This study was supported under contract SANL 284 from the Lawrence Livermore Laboratory.     

Major features of frequency sweeping of emission from heterojunction quantum lasers

We have used numerical modeling to establish the major features of the variation (sweeping) of the “ instantaneous” laser frequency of heterojunction quantum lasers as a function of the pump current modulation frequency and tuning of the lasing frequency within the gain band. The active medium is described within a two-band model with identical distribution of levels for the electron and hole subbands, assuming transitions with no selection rule between the ground-state subbands. Sweeping of the laser frequency occurs due to variation of the refractive index of the active medium, as a result of the variation in the concentration of nonequilibrium charge carriers. Laser frequency sweeping does not occur for low current modulation frequencies, corresponding to realization of the quasisteady-state lasing regime. In the other limiting case of relatively high current modulation frequencies, the modulation depth of the laser output also tends toward zero. The magnitude of the sweep is greatest in the intermediate current modulation frequency region. For a specified current modulation frequency, the dynamic shift of the laser mode depends on the position of the lasing frequency within the gain band. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 223–229, March–April, 2007.     

A UV–Visible–NIR fluorescence lifetime imaging microscope for laser-based biological sensing with picosecond resolution

This article describes the design and characterization of a wide-field, time-domain fluorescence lifetime imaging microscopy (FLIM) system developed for picosecond time-resolved biological imaging. The system consists of a nitrogen-pumped dye laser for UV–visible–NIR excitation (337.1–960 nm), an epi-illuminated microscope with UV compatible optics, and a time-gated intensified CCD camera with an adjustable gate width (200 ps-10^-3 s) for temporally resolved, single-photon detection of fluorescence decays with 9.6-bit intensity resolution and 1.4-μm spatial resolution. Intensity measurements used for fluorescence decay calculations are reproducible to within 2%, achieved by synchronizing the ICCD gate delay to the excitation laser pulse via a constant fraction optical discriminator and picosecond delay card. A self-consistent FLIM system response model is presented, allowing for fluorescence lifetimes (0.6 ns) significantly smaller than the FLIM system response (1.14 ns) to be determined to 3% of independently determined values. The FLIM system was able to discriminate fluorescence lifetime differences of at least 50 ps. The spectral tunability and large temporal dynamic range of the system are demonstrated by imaging in living human cells: UV-excited endogenous fluorescence from metabolic cofactors (lifetime ∼1.4 ns); and 460-nm excited fluorescence from an exogenous oxygen-quenched ruthenium dye (lifetime ∼400 ns). Received: 23 February 2003 / Published online: 22 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-734/9361-905, E-mail: mycek@umich.edu