Enhanced efficiency and extended wavelength range of dye lasers operated with DCM

It is observed that the efficiency of the DCM dye dissolved in ethylene glycol benzyl alcohol can be enhanced if the dye is preheated at a temperature of 150 °C. Peak powers as high as 1.5 W have been achieved with a single-mode ring dye laser at 640 nm when pumped by 9 W (all lines) from an argon-ion laser. The wavelength region has been also extended beyond both ends of the tuning curve compared to a conventionally prepared DCM dye. Received: 3 September 1999 / Revised version: 9 December 1999 / Published online: 23 February 2000     

Fast local intensity fluctuations in a pulsed untuned dye laser

Intensity fluctuations in a pulsed dye laser are studied. Fluctuations are local and very fast. The onset of the fluctuating regime coincides with the laser threshold. The average Fourier spectrum of fluctuations shows three broad peaks at frequencies v ₁=55 MHz, v ₂=110 MHz, v ₃=165 MHz. The three frequencies remain unchanged when resonator geometrical and optical parameters are changed. Nevertheless the amplitude of fluctuations is easily affected by such changes and by the solution temperature. The application of the Grassberger-Procaccia algorithm to the experimental fluctuations gives slope convergence (between 3 and 5) in some cases. This seems to indicate that the origin of fluctuations is chaotic-deterministic.     

Picosecond and subpicosecon pulse generation in synchronously pumped mode-locked cw dye lasers

Generation of tunable near-infrared picosecond and subpicosecond pulses in a synchronously pumped cw mode-locked Oxazine-1-perchlorate dye laser has been investigated for different values of the important system parameters. The experimental results confirm the predictions of a simple theoretical model which describes the steady-state pulse duration in terms of gain modulation strength, pump power, intracavity bandwidth, pump pulse length and cavity detuning. For a pump-pulse length of 100 ps and a bandwidth of more than 500 Å for the intracavity tuning element dye-laser pulses as short as 0.35 ps have been obtained. Under these conditions up to 100 mW of average output power were provided. In addition, mode-locking of an Oxazine 750 dye laser by synchronous pumping with the cw train of pulses obtained from the Oxazine-1-Perchlorate laser is reported.     

Photoacoustic studies and selective ablation of vascular tissue using a pulsed dye laser

The optical attenuation coefficient for human aorta has been measured in the 440–500 nm spectral region using the transient photoacoustic (thermoelastic) response produced by an excimer-laser-pumped dye laser. It is confirmed that diseased tissue has a significantly higher attenuation than normal samples in this spectral region. The maximum difference occurs at 480 nm and there is a lowering of the ablation threshold fluence for diseased tissue by a factor of 1.5 for dye laser ablation at this wavelength.     

Subpicosecond pulse generation in synchronously pumped and hybrid ring dye lasers

Subpicosecond pulse generation has been examined in synchronously pumped mode-locked ring dye laser systems. These include hybrid and composite absorber/gain media arrangements as well as a simple synchronous cavity. The shortest pulses recorded were 0.3 ps for the hybrid system, and this has been shown to be critically dependent on the positioning of the absorber jet in the centre of the cavity to better than 50 m. Stable operation for subpicosecond pulse generation has been achieved in the ring configuration with greater wavelength tunability and higher average power conversion efficiency than with conventional cavity arrangements.     

High-brightness ultraviolet excimer lasers

At present the performance of short-pulse rare-gas-halide excimer-laser systems is definitely below that of solid-state systems, as far as the maximum peak-power is concerned. However, short-pulse excimer lasers are expected to be the best candidates to produce the highest focused intensities (I 10²⁰ W/cm²) provided by the shorter wavelength and less optical distortion in the gaseous active medium. This is especially feasible if the present performance of short-wavelength focusing optics is improved, and the problem of the limited extraction efficiency of excimers is solved. In this paper the results of former developments, novel methods, such as spatially-evolving chirped-pulse amplification, off-axis amplification, interferometric multiplexing, and some considerations for the achievable maximum brightness of table-top excimer systems are presented.     

Linear and cross-linked polymeric solid-state dye lasers based on 8-substituted alkyl analogues of pyrromethene 567

The lasing properties of analogues of the commercial laser dye pyrromethene 567 (PM567) incorporated (dissolved or copolymerized) into polymeric matrices have been studied using both linear and cross-linked methyl methacrylate-based copolymers with different degrees of functionalization. All synthesized dyes have the chromophore core of PM567 but with an ω-acyloxypolymethylene chain at position 8. In general, the new materials exhibited laser emission with higher efficiencies and much higher photostabilities than those containing the commercial dye PM567 under the same experimental conditions. Lasing efficiencies of up to 40% were obtained under transversal pumping at 534 nm. The highest photostabilities, with the laser output remaining stable or dropping by less than 15% after 100 000 pump pulses at the same position of the sample, were reached in cross-linked materials with dyes covalently linked to the polymeric chains. When the polymeric samples were incorporated into a grazing-incidence grating oscillator, narrow-line-width operation with tuning ranges of up to 40 nm was obtained. These results show that efficient and photostable solid-state dye lasers competitive with their liquid counterparts can be developed by adequate chemical modifications in the dye molecules, as well as by the selection of appropriate polymeric formulations.     

Spectral purity of pulsed dye lasers

High-spectral purity of pulsed dye lasers is required by many experiments. Unfortunately, the dye laser output is usually accompanied by a spectrally broadband background of spontaneous emission (ASE). We have carried out detailed studies of the ASE background using a dye laser operating with an oscillator, pre- and main amplifier.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

Single-longitudinal-mode selection in a nanosecond-pulsed dye laser

We investigate the dynamics of the excited-state population, the cavity photon number, and the spectrum of an optically pumped nanosecond-pulsed dye laser containing bandwidth-narrowing elements in the cavity. We show that, in order to achieve single-mode operation, the pump-pulse duration has to be long enough and the dye concentration sufficiently high. This is partly due to the frequency shift of the laser spectrum during the decrease of the excited-state population towards its steady-state value. We demonstrate a single-mode dye laser, where single-mode selection is realised with the aid of an intracavity Fox–Smith interferometer. In this way we have obtained 5-ns-long pulses at the wavelength of 590 nm with a pulse energy of 6 mJ and a spectral width of 100 MHz (FWHM). Received: 3 December 2001 / Published online: 14 March 2002     

A versatile photoacoustic spectrometer for sensitive trace-gas analysis in the mid-infrared wavelength region (5.1–8.0 and 2.8–4.1 μm)

A versatile CO laser-based photoacoustic spectrometer is presented equipped with three photoacoustic cells placed inside the laser cavity. The newly designed CO laser can operate both in the Δv=1 and the Δv=2 modes (5.1–8.0 μm and 2.8–4.1 μm) on 400 laser lines. Improved laser operation originating from a better cooling of the gas discharge was evidenced by a shift of the laser output power to lower J-values. Due to the wide emission range of the source, many molecules of biological and atmospheric interest, including methane and ethane, can be detected with sensitivities typically at the (sub)ppb level. Measurement of the respiration of a cockroach showed that the spectrometer is not only sensitive, but also has a good time response (8 s at a flow rate of 10 l/h). Received: 3 April 2002 / Revised version: 14 June 2002 / Published online: 21 August 2002 RID="*" ID="*"Current address: Soegijapranata Catholic University, Department of Food Technology, Jalan Pawiyatan Luhur IV/1 Bendan Duwur, P.O. Box 8033/SM, Semarang 50234, Indonesia RID="**" ID="**"Current address: Sanata Dharma University, FMIPA, Kampus III, Paingan, Maguwoharjo, Depok, Sleman, Tromol Pos 29, Yogyakarta 55002, Indonesia RID="***" ID="***"Corresponding author. Fax: +31-24/365-3311, E-mail: fransh@ sci.kun.nl     

Lasing mechanism in two-dimensional photonic crystal lasers

We conduct a comprehensive investigation of the lasing mechanism in a photonic crystal slab laser with a refractive index that is periodic in two dimensions. Experimental spectra of laser structures fabricated with organic gain media are presented. It is found that lasing frequencies can be explained in terms of Van Hove singularities in the density of modes. We also observe lasing spectra that cannot be obtained from structures with one-dimensional periodicity, such as traditional distributed feedback lasers. Lasing frequencies are computed using numerical techniques. Received: 7 April 1999 / Accepted: 12 April 1999 / Published online: 19 May 1999     

Photophysical properties and laser characteristics of a new rigid aminocoumarin dye lasing in the blue-green region

The photophysical properties of a new dye, 7-Diethyl AminoCoumarin with a Rigid substitution in the 3-position (referred to as DARC) have been studied in three solvents: dioxane, DMF and DMSO. The dye has been found to have a fluorescence quantum efficiency (_fl) between 0.40 and 0.80 in these solvents. The dye-laser performance of this dye has also been investigated in dioxane, DMF and DMSO, under nitrogen-laser pumping and compared with that of the commercially available standard laser dye, Coumarin 515 (C-515). A tuning range of nearly 70 nm was obtained in the blue-green region with an efficiency up to 80% of that of the standard dye. The observed characteristics of the dye are explained in terms of the sructural rigidization of the dye in the 3-position which inhibits the formation of the Twisted Intramolecular Charge Transfer (TICT) conformation in the excited state leading to an enhancement of the _fl and a considerable improvement in the laser performance.Research carried out at U.D.C.T., Bombay, India     

Photoacoustic multicomponent gas analysis using a Levenberg–Marquardt fitting algorithm

2 laser photoacoustic spectrometer has been developed for the in-situ monitoring of atmospheric trace gases in different environments. Numerous air pollutants, such as ammonia, ethene, ozone and alcohols, can be monitored with a time resolution of a few minutes. A new fitting algorithm based on the numerical method of Levenberg–Marquardt is discussed and applied to the derivation of individual gas concentrations from measured photoacoustic signal amplitudes and phases at selected CO₂ laser wavelengths. The algorithm has been tested with artificially generated multicomponent gas mixtures exhibiting gas concentrations in the ppb to ppm range. Furthermore, its potential is demonstrated with the analysis of an air sample from a fruit storage chamber and with ambient air measurements during a field study in a rural environment. Received: 23 March 1998/Revised version: 18 June 1998     

Polarization and power characteristics of pulsed dye lasers with transverse pumping

Starting from the classical theory on molecular luminescence in liquids, rate equation for two-polarization-mode laser oscillation under transverse pumping with intense excitation have been set forth neglecting the influence of orientational relaxation of the dye molecules. Hence, the laser output power and polarization under different configurations have been obtained. The results show that the dye laser is partially polarized even when the pump beam is unpolarized and no polarizing elements exist in the cavity. If we define a reference plane consisting of the axes of the pump beam and the dye laser, the laser system has to adopt the plane perpendicular to the reference plane as the polarization direction in order to yield a highly efficient, linearly polarized laser output. Experiments on a copper-vapor laser pumped dye laser verified these analytical results.     

Single picosecond UV pulse generation by mode-locking of an excimer laser-pumped dye laser

A single picosecond ultraviolet pulse has been generated based on mode-locking of a dye laser pumped by a long pulse XeCl laser to serve as the input source for a high-power ps KrF laser system. A short-pulse uv dye laser (BBQ) pumped by an additional XeCl laser was used to selectively amplify a single pulse from a mode-locked pulse train with the pulse separation of 3.2 ns. The amplified single pulse was frequency-doubled to 248 nm with the pulse duration of 20 ps.     

Laser characteristics of a new laser dye: 7-Diethylamino-3-Styryl Benzimidazo (1,2-a) Quinoline

The laser characteristics of a new dye, 7-Diethyl-amino-3-Styryl Benz31 yimidazo (1,2-a) Quinoline (DSBQ) have been investigated in two solvents: DiMethylSulfOxide (DMSO) and DiMethylFormamide (DMF) by excitation with a pulsed nitrogen laser and compared with that of the standard dye rhodamine B. The lasing range of the dye is nearly 40 nm with maxima at 635 nm and 625 nm in DMSO and DMF, respectively. The efficiency of this dye (DSBQ) has been found to be better than half that of rhodamine B.     

Intracavity photoacoustic gas detection with an external cavity diode laser

The first use of an external cavity diode-laser light source in combination with a photoacoustic detector for high-sensitivity gas detection is described. This combined system is applicable for detecting gases with absorption coefficients as low as 5 x 10^–8 cm^–1 by operating the photoacoustic cell in an intracavity mode. Measurements were made on the 1.13 m absorption lines of water vapour. For quantitative measurements, it was found to be necessary to introduce a reference cell into the system.     

Efficient and highly photostable solid-state dye lasers based on modified dipyrromethene.BF2 complexes incorporated into solid matrices of poly(methyl methacrylate)

We report on the laser action of modified dipyrromethene.BF₂ complexes both dissolved in poly(methyl methacrylate) and copolymerized with methyl methacrylate. All recently synthesized dyes have the chromophore core of laser dye pyrromethene 567, differing in the substituent in position 8. The new dyes showed important and most significant increases in both lasing efficiency and photostability. When the laser samples were pumped transversely at 534 nm, laser emission was obtained with efficiencies of over 30% in most cases, to be compared with a lasing efficiency of 12% exhibited by reference dye pyrromethene 567 under the same experimental conditions. Some of the materials exhibited highly photostable laser action, with no sign of degradation in the laser output after 60000 pump pulses at the same position of the sample at a repetition rate of 10 Hz, whereas the laser emission of reference dye pyrromethene 567 dropped to zero after less than 40000 pump pulses. Received: 19 November 2002 / Revised version: 20 February 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +34-91/564-2431, E-mail: acostela@iqfr.csic.es     

Highly efficient synchronous amplification of a picosecond dye laser at a kHz repetition rate

A short pulse, high energy, high repetition rate dye amplifier with superior conversion efficiency is reported. The dye amplifier is composed of three single-pass dye cells, longitudinally pumped by a frequency doubled 1 kHz Nd: YLF regenerative amplifier. The dye amplifier yields 3.5 ps, 150 J pulses at 595 nm, corresponding to a 12% conversion efficiency. The ASE is 1% or less, and the transverse mode quality is near-Gaussian.In absentia from the Department of Chemistry, Princeton University, Princeton, NJ 08544, USA     

Tunable sub-100 femtosecond dye-laser pulses generated with a nanosecond pulsed pumping

Subpicosecond pulses at a fixed wavelength produced with a low-Q cavity dye laser pumped by a single, nanosecond laser (Q-switched Nd:YAG) are converted into tunable high-power sub-100 femtosecond pulses by generation, spectral selection, amplification and compression of a supercontinuum. The tunable, chirped, high-energy pulses obtained are compressed with a prism pair. Energies up to 50 J in sub-100 fs pulses were obtained in the 540 to 650 nm range using 40 mJ of the Nd: YAG-laser pumping pulses at 532 nm. The whole sub-100 fs system including the low-Q dye laser uses only one Nd:YAG laser as a pump source.