Narrow resonances of two-photon absorption of super-narrow pulses in a gas

First cw laser oscillation with thresholds below 1 mW was observed for various B¹П_u → X¹ ∑ _g ⁺ transitions of diatomic molecular sodium excited by different argon laser lines in the range of 454–488 nm. For pump powers of 0.5 W output powers up to 3 mW and single-pass gain up to 0.1 cm⁻¹ were obtained. Some properties of the heat pipe laser system are discussed.     

Travelling-wave amplified spontaneous emission excited in a prismatic geometry

A new experimental realisation of the travelling-wave amplified spontaneous emission (TWASE) is described utilising a prismatic arrangement to get the pulse front delay in the pump beam. Rhodamine dye solutions were pumped by the amplified 25 ps long 555 nm pulses of a distributed feedback dye laser. The pulse shortening in the TWASE resulted in 12 ps output pulses with 18% energy efficiency. The observed spectrum showed numerous lines, and it contained the amplified Raman line of the pump beam. Several spots were found in the far-field zone of the generated TWASE.     

Theory of travelling-wave amplified spontaneous emission

A rate-equation model for describing the travelling-wave amplified spontaneous emission pulses (TWASE) in a transversally excited travelling wave arrangement is given. 6.35 ps long ASE pulses have been obtained by 12 ps long pump pulses. The effect of pump intensity, pump-pulse duration, molecular parameters of the dyes and pump-sweep velocity on the ASE pulses is studied.     

Picosecond pulse shortening by travelling wave amplified spontaneous emission

A new scheme for travelling-wave excitation of amplified spontaneous emission (ASE) employing transversal pumping is presented. ASE pulses emitted in the forward direction had a duration of 6 ps, corresponding to one half of the pump pulse duration. The spectrum was strongly structured, with individual components having a width of 0.1–1.0 Å. Essential characteristics of longitudinal and transversal excitation of travelling wave ASE are compared.     

Amplified spontaneous emission in short-pulse excimer amplifiers

We have found a simple analytical expression which describes the relation between amplified spontaneous emission (ASE) and small-signal gain in short-pulse amplifiers. It is also shown that the contrast of the short pulse to the ASE is weakly dependent on the saturation of the ASE, and influenced mainly by the saturation of the short pulse. The theoretical considerations were verified by measurements.     

Effect of laser dye deterioration on performance

Loss of gain in a dye medium as a result of decomposition by pump photons is considered in terms of disappearance of dye molecules and the appearance of a new, single chemical product having absorption in the fluorescence band. The cases of small signal gain and saturated gain are applied to a single pass through a transversely excited amplifier. Loss of output, defined as “quantum yield of laser deterioration”,Q _L , is related to the true quantum yield of molecular destruction of the dye,Q _M , and other known parameters. For the experimentally common, saturated gain condition, the smallestQ _L can be isQ _M , which requires a photochemically bleachable dye with high gain, preferably at high concentration, in a long cavity, operating at high injection and pumping fluxes. Reversing these conditions, the highest valueQ _L can be, compared withQ _M , is unrestricted. This work was performed under the auspices of the U.S. Energy Research and Development Administration. Contract No. W 7405 Eng 48.     

Selective action on nucleic acids components by picosecond light pulses

We report on first attempts for selective action on nucleic acid components, namely uracil and adenine, using picosecond light pulses. Selective action was achieved both in the case of irradiation of mixtures of bases and in the case of irradiation of mixtures of different nucleic acids components, which contain uracil and adenine.     

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     

Stepwise photoionization of complex organic molecules in the gas phase induced by UV laser radiation

We measured the photoionization cross-sections of anthracene, 1,2-benzanthracene,p-terphenyl, and 2,5-diphenylfuran molecules excited to the singlet and triplet electronic states intermediate in the stepwise two-photon ionization process at 266 nm (all compounds) and at 355, 391 and 417 nm (anthracene).     

Solvent dependent characteristics of XeCl pumped UV dye lasers

The characteristics of near uv dye lasers pumped with short duration, 308 nm pulses from a XeCl laser are described with particular emphasis on the parameters influencing high average power operation. The solvent is shown to effect the operation of all dye lasers studied, particularly the photochemical stability. Measurements of the efficiency, as a function of the integrated pump energy have been made for a series of dye-solvent combinations. With the best combinations, average output powers in excess of 1W and conversion efficiencies greater than 25% were obtained at a repetition rate of ∼100 Hz.     

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.     

Characterization of a Br(2P1/2)–CO2(1001-1000) transfer laser driven by photolysis of iodine monobromide

2 laser operating on the 10⁰1-10⁰0 transition at λ=4.3 μm and pumped by E –V energy transfer from Br(²P_1/2) has been demonstrated. The dynamics and performance of this device were characterized by observing the time-resolved stimulated emission and the steady-state spontaneous side fluorescence after photolysis of IBr or Br₂ by a frequency-doubled Nd:YAG laser or Ar⁺ laser, respectively. Although the E –V excitation kinetics are favorable, rapid vibrational relaxation limits laser action to CO₂ pressures of less than 1 Torr. Numerical modeling of laser pulse shapes and the dependence on IBr and CO₂ pressure and photolysis energy establish a relatively high gain of 0.33%/cm, a CO₂-pressure-dependent optical loss of 0.04–0.06%/cm, and an efficiency of 2×10^-5 4.3-μm-laser photons per incident photolysis photon. The CO₂ fluorescence after photolysis of a fixed Br₂/CO₂ gas mixture decreases as a function of photolysis time by about 30%/h, indicating the photolytic production of an important quencher. Received: 23 June 1997/Revised version: 23 September 1997     

Photophysical parameters for potential vapour-phase dye-laser media

The fundamental photophysical parameters of the organic scintillators, anthracene, 9, 10 dimethyl antracene (DMA), 9, 10 diphenyl anthracene (DPA), 2-(1-napthyl)-5-phenyloxazole (α-NPO) and 2, 2′-p-phenyl bis (5-phenyloxazole) (POPOP), were investigated in the liquid and vapour phases. Their ground state, triplet-triplet and fluorescence spectra were determined and accurate extinction coefficients obtained. Photodecomposition of POPOP vapour under 337 nm excitation was investigated in detail and a photodecomposition quantum yield of 1.1×10⁻² obtained at 568 K. The POPOP triplet state in the vapour phase is quenched by the addition of 1, 3, 5, 7 cyclo-octatetraene and a quenching rate constant of 2.9×10¹⁰ M⁻¹ s⁻¹ was determined.     

Laser emission under flashlamp pumping of a new crystal: Nd-doped strontium-lanthanum-aluminate (Nd:ASL)

1-x Nd_yLa_x-yMg_xAl_12-xO₁₉) is a new material, tunable in the 1–1.1 μm band. We present the first results of pulsed laser emission of this crystal under flashlamp pumping. We obtain a slope efficiency of 3.3% with a maximum average power of 40 W at 40 Hz in free-lasing regime. Nd:Cr codoping of ASL is also tested, but with much lower efficiency. Received: 12 June 1998/Revised version: 30 September 1998     

Amplification and wave mixing of induced and spontaneous emission in semiconductor laser amplifiers

We theoretically describe and experimentally investigate the spatio-spectral wave mixing of induced and spontaneous emission in large-area InGaAs-semiconductor laser amplifiers. The dynamic light-matter-coupling is described by a spatially resolved theory based on Maxwell–Bloch–Langevin equations, taking into account many-body-carrier interactions, energy transfer between the carrier and phonon systems and, in particular, the spatio-temporal interplay of stimulated and amplified spontaneous emission and the noise caused by spontaneous emission. Our numerical model reveals the fundamental physical processes which are responsible for the spectral power distribution of the amplified laser light and predicts the emission properties of high-power semiconductor laser amplifiers, such as emission spectra and input power–output power characteristics. Received:30October2002/Revisedversion:21November2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-711/6862-349, E-mail: Edeltraud.Gehrig@dlr.de RID="**" ID="**"Also at: Institute of Physics, Tampere University of Technology, P.O. Box 692, FIN-33101, Tampere, Finland RID="***" ID="***"Present address: Heidelberger Druckmaschinen AG, Speyerer Strasse 6, 69115 Heidelberg, Germany RID="****" ID="****"Present address: Lightbit Corporation, 411 Clyde Avenue, Mountain View, CA 94043, USA     

Pure MW Raman laser emission in superradiant mode in ammonia by pumping with 9P20 CO2 laser line

In this work, clear FIR Raman emission in ammonia was observed when a 9P20 CO₂ line was used as a pump. We have noted an intense pump depletion and strong superradiant FIR and MIR emissions. The time history of these radiations has also been recorded. The intense MIR radiation is a new line observed in the ammonia laser.     

The vibrational relaxation time constant for theB v=0 level of XeCl

The vibrational relaxation time constant for theB _v=0 vibrational level of XeCl^* has been investigated by observing the coupling between theB _v=1 andB _v=0 vibrational levels under saturated lasing conditions. Based on this observation, estimates of the expected extraction efficiency from theB-state have been made.     

Influence of collisional coupling on the energy extraction from theB,C, andD state in KrF

Collisional coupling between theB, C, andD states of KrF is measured in a discharge pumped KrF laser. Detection of the time resolved populations in the three states via measurement of the side fluorescence in theB→X, C→A, andD→X bands is used to record the collisional relaxation from theC andD state to theB state during laser emission. The experimentally determined limits for the collisional coupling times are τ_B-C≦1 ns and τ_B-D,τ_C-D<20 ns at total pressures of 2 bar. Investigation of theB→X fluorescence band shows that the vibrational manifold of theB state is not thermalized during laser emission. TheV-V,T coupling time is estimated to be τ_V-V,T=4±2 ns. The influence of collisional coupling on energy extraction in the KrF laser is discussed.     

Gain depletion due to amplified spontaneous emission in multi-pass laser amplifiers

Calculations of the effects of amplified spontaneous emission (ASE) in laser amplifiers designed to amplify sub-picosecond pulses are presented. A one-dimensional code is used with some simple approximations to account for aspect ratio variation in cases of cylindrical symmetry. Gain depletion due to ASE is compared for various multi-pass geometries. Optimisation for short pulse amplification of a telescopic, beam-expanding, 4-pass amplifier is considered.On leave from Electrotechnical Laboratory, Tsukuba, Ibaraki, Japan