The physical mechanisms important to the operation of tunable lasers utilizing organic dyes are discussed. The uniqueness of organic dyes as a tunable laser medium is reviewed by investigating the optical properties of two broadened energy levels. The complete energy level system is investigated and gain and efficiency are calculated. The wide variety of practical laser configurations possible for optically pumped dye lasere are examined. New topics of interest such as dye vapor lasers and short pulse generation are discussed.

Physics of dye lasers

Several silylated coumarin dyes with different linkages and degrees of functionality have been synthesized and incorporated in both SiO2 xerogels and various solvent hosts. The absorption and fluorescence spectra were examined to explore selected structural and environmental effects on the optical properties of these dyes. Silylated dyes (also referred to as grafted or functionalized dyes) are dye molecules that have been chemically altered to provide alkoxysilane functionality allowing the active molecule to be covalently bonded to the host. Silylation of dye molecules had little effect on the absorption and fluorescence spectra in neutral solvent environments. The optical spectra of silylated dyes compared to those of their conventional counterpart were less influenced by the local chemical environment (e.g., pH) and thus allow for greater control and stability of the fluorescent properties of the dyes in different host environments. Spectroscopy during the drying/gelling of a derCoum xerogel film conta...

Silylated Coumarin Dyes in Sol-Gel Hosts. 1. Structure and Environmental Factors on Fluorescent Properties

The application of acoustic emission (AE) measurements to locate the sources of fracture of a single high-strength fibre embedded in an epoxy matrix which is loaded in tension is described. From the micromechanical model and the fragment length distribution, interfacial shear strength values were calculated. The technique is demonstrated for small-diameter glass and graphite fibres as well as for fibres which exhibit fibrillar fracture, such as Kevlar and PBZT. Good agreement is found between the mean fragment length values obtained by optical and AE measurements for glass and graphite fibres. Values obtained for interfacial shear strength by the AE technique are comparable with those obtained using other techniques.

Determination of fibre/matrix interfacial shear strength by an acoustic emission technique

Laser gain determination by means of amplified spontaneous emission is discussed in terms of a rate-equation approach Numerical solutions show that optical gain can be deduced only for a limited regime of experimental parameters The theoretical analysis is examined with experimental gain data for organic dyes in the vapor phase and in liquid solution In addition, the gain of electron-beam-excited Ar–N2 and XeF laser mixtures has been studied

Laser gain measurements by means of amplified spontaneous emission.

The ultrafast dynamics of site-specific hydrogen bonds between an organic chromophore serving as hydrogen acceptor and a hydrogen-donating species in solution is studied by femtosecond vibrational spectroscopy. This new method gives specific insight into microscopic structural changes of hydrogen bonds initiated by electronic excitation of the chromophore. We study H-bonded complexes of coumarin 102 with the solvent CHCl3, and with phenol. Upon electronic excitation, the intermolecular hydrogen bond between proton donor and acceptor is cleaved within 200 fs, followed by a slower reorientation dynamics of the donor molecules extending into the picosecond regime. For CHCl3, this slower rearrangement is interpreted in terms of polar solvation. In complexes consisting of a coumarin molecule and two phenol moieties, the slower dynamics is related to geometry changes of the phenol–phenol hydrogen bond. The consequences of those results for a microscopic picture of polar solvation are discussed.

Hydrogen-Bond Dynamics and Solvation of Electronically Excited States as Determined by Femtosecond Vibrational Spectroscopy

The emission characteristics of the coumarin-dye 4-Methyl-umbelliferone (4-MU) are investigated by studying the low-intensity fluorescence spectra and the laser-pumped gain spectra for various solvents and pump powers. A total of five different forms were found to exist, each of which can be isolated in a proper solvent. Of the five species, I is the neutral molecule, two others (II and V) are results of ground-state reactions, while two (III and IV) are produced by excited-state reactions and do not have a stable ground state. By proper adjustment of the solvent a number of combinations of the five forms can coexist and lase together, giving rise to a variety of gain spectra and allowing the possibility of "tailoring" a desired gain curve over most of the visible spectrum. Comparison of the gain and fluorescence spectra indicates the presence of triplet or excited-state losses in some of the forms, yields comparative values of emission parameters, and reveals an acidity-dependent quenching of one of the excited-state species.

Characteristics of the 4-methylumbelliferone laser dye

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Characteristics of the 4-methylumbelliferone laser dye