Coumarin Laser Dyes Research Articles

Resonance enhanced dynamic Rayleigh scattering

A semiclassical theory relating the molecular resonance Rayleigh scattering intensity to the extinction coefficient of an electronic transition is presented. For isotropic molecules, the theory is shown to be equivalent to classical fluctuation theory. The semiclassical theory is then extended to include anisotropic polarizabilities. Depolarized scattering intensities and depolarization ratios are calculated for a model system, and the general features of previous experimental data are explained. Inclusion of inhomogeneous broadening in the theory predicts increased scattering intensities and decreased vibrational resolution of the scattering profile. Depolarized Rayleigh linewidths and intensity profiles are presented for a series of diphenylpolyenes, several coumarin laser dyes, and 3,4-dinitrophenol in its neutral and ionic forms. The ideal molecular properties and experimental conditions for the use of resonance enhanced dynamic Rayleigh scattering are deduced.

Excited singlet absorption in blue laser dyes: Measurement by picosecond flash photolysis

Absorption from the lowest relaxed excited singlet state in the laser dyes POPOP, carbostyril 165, 4-methylumbelliferone, 7-diethylamino-4-trifluoromethylcoumarin, and coumarin 30 has been measured over the range, approximately, from 350 to 650 nm. In addition, rhodamine 6G was remeasured to permit comparison of our procedures with previous work and to help promote the emergence of a standard substance which all laboratories may use to test and refine their procedures. For comparison, 9,10-diphenylanthracene was investigated as an example of an "unsuccessful laser dye." Measurements were made using excitation pulses of 40 ps duration at 347 nm and a continuum probe, of the same duration, delayed by 200 ps.

Active mode-locking of lasers using GaAs and GaP picosecond switches

Active mode-locking of coumarin dye lasers has been achieved using either a GaAs or GaP picosecond high voltage switch to drive an intra cavity Pockels cell in a Q modulation technique. Pulses of 30–50 ps were generated with a peak power of ≈500 kW, while pulses as short as 20 ps were observed. The method can be generally applied to various laser systems over wide spectral ranges.

Medium effects on fluorescence quantum yields and lifetimes for coumarin laser dyes

Fluorescence quantum yields and lifetimes of coumarin dyes are sharply reduced in polar solvents if amine substituent groups are free to rotate. The polar solvent effect is interpreted in terms of relaxation of excited dye from an initial planar conformation to a twisted zwitterionic state.

Measurement of Fluorescence Lifetimes of Coumarin Laser Dyes with a Mode-Locked Krypton Ion Laser

Abstract The fluorescence lifetime of four coumarin laser dyes (C-7, C-30, C-102, and C-120) were measured in three different solvents (methanol, ethanol and water) a t dilute and lasing concentrations. The lifetime generally decreases for the more hydrophobic dyes as the solvent polarity increases. There is little change with concentration due to the large Stokes shift.

Tunable blue picosecond pulses from a flashlamp-pumped dye laser

A flashlamp-pumped coumarin dye laser mode locked passively with a saturable absorber 3,3′-dihexyloxacarbocyanine iodide (DOCI) has produced tunable picosecond pulses shorter than 10 ps in the blue region of the spectrum between 475 and 490 nm. A single pulse switched from the train was used for fluorescence lifetime measurements. The excited-state lifetime τ of DOCI in pure ethyleneglycol was 505±10 ps.

Molecular constants for the 010 level of the [formula omitted]2B 1 ground state of NH 2

The A 2A 1— X 2B 1 emision spectrum of NH 2 has been investigated (a) with moderate resolution (±1 cm −1) by excitation with a coumarin dye laser and (b) with higher resolution (±0.02 cm −1) by excitation in a microwave discharge. Rotational assignments have been made for bands (0,υ′ 2,0) → (0,0,0) and (0,υ′ 2,0) → (0,1,0) with υ′ 2 = 12, 13, 14 and 15. Term values have been established for 93 rotational levels of the 010 level of the ground state and have been fitted with a standard deviation of 0.032 cm −1 to a hamiltonian with fifteen molecular constants. A table of term values is given for the 010 level up to the 8 ϵ0F 1 and F 2 rotational levels.

Wavelength-tunable optical mixing experiments between 208 nm and 259 nm

Sum-frequency generation experiments in which the second harmonics of rhodamine and coumarin dye lasers are upconverted to the 208-234 nm by mixing with 1064 nm are described. The dye lasers were pumped by the second and third harmonics of a repetitively pulsed Nd:YAG laser. Both temperature-tuned and angle-tuned phase matching techniques were used with mixer crystals of ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP). Tunable light from 246 nm to 259 nm also was generated by mixing the output of a coumarin laser with the 532-nm harmonic of the Nd:YAG laser. Peak powers between about 500 W and 10 kW were obtained, and both theoretical and experimental tuning curves have been determined for these processes. Limitations imposed by mode beating effects in the Nd:YAG laser and by the relatively broad linewidth of the dye lasers are discussed.

Optical backward parametric fluorescence in sodium nitrite

We present the first observation of optical backward-traveling-wave (BTW) parametric fluorescence, in a sodium nitrite crystal pumped by a coumarin dye laser. Several aspects of BTW parametric interactions are discussed. This experiment provides a feasibility test of optical BTW parametric oscillators.

Photochemical products in coumarin laser dyes

The photochemical degradation processes occurring in a flashlamp-pumped dye laser using an ethanol solution of 7-diethylamino-4-methylcoumarin have been investigated in detail. The pump radiation gives rise to two irreversible reaction paths, resulting in a total of five photochemical products. One of these substances inhibits laser action because of its optical absorptivity at laser wavelengths. Suggestions for extending dye lifetimes based on this investigation are given.

Benzocoumarins, a New Family of Laser Dyes

Coumarin compounds are efficient fluorescers, and several of them have been tested for their laser properties1–5. Of particular interest is the wide tunability resulting from the tautomerism of 7-hydroxycoumarins. The structure of 4-methylumbelliferone (4MU) (I) or 4-methyl-7-hydroxy-coumarin is shown in Fig. 1. We have designed, synthesized and tested the hydroxybenzocoumarins for their spectral and laser properties. We have designed these compounds with the intention of obtaining a compound with the wide laser tunability of 7-hydroxycoumarins but with a tunability range beyond the green region of the spectrum which coumarin laser dyes cover. The increase in the π conjugation length in organic molecules is in general accompanied by the bathochromic shift in the absorption and emission spectra. The tautomerism mechanism which we have proposed suggested that the conjugation length between the carbonyl and the hydroxyl groups is the major factor determining the fluorescence λmax. Therefore, the extension of the conjugation from hydroxycoumarins to hydroxybenzocoumarins was made between those groups. (The only benzocoumarin compound reported in the literature as a laser dye is 3-carboxy-5,6-benzocoumarin, which does not contain any hydroxyl group5.) Also, the tautomerism mechanism is satisfied only if the hydroxyl group is placed at specific carbon atoms of benzocoumarin. We have synthesized these compounds, which can be prepared in one step from the commercially available chemicals. Compounds II-VI shown in Fig. 1 have been prepared. Compounds III, V, and VI are reported for the first time in the literature. (By the Chemical Abstracts nomenclature system, III, V, and VI are 9-hydroxy-1 -trifluoromethyl-3H-naphtho[2,1-b]pyran-3-one, 8-hydroxy-4-trifluoromethyl-2H-naphtho[1,2-b]pyran-2-one and 8-hydroxy-4-phenyl-2H-naphtho[1,2-b]pyran-2-one, respectively.)

Formation mechanisms in an excited-state-reaction dye laser

The formation mechanisms in an excited-state-reaction coumarin laser dye are investigated by measurements of the saturation characteristics of the laser. By recording the influence of intense cavity oscillation on the single- and double-pass amplified spontaneous emissions of the two different ``exciplex'' species, it is found that a ``serial'' model applies, the green-emitting species being formed from the blue-emitting one.

Observation of inhomogeneity in the gain spectrum of a coumarin laser dye

The gain spectra of 4-methylumbelliferone (4-MU) solutions are measured at various solvent acidities and pump powers using an automated, computer processed system. The gain spectra are compared to the low intensity fluorescence spectra. The two excited state reaction species are found to contribute to the total gain in varying proportions depending on solvent acidity. The green fluorescing species is quenched at high acidities. Some possible explanations of this effect are suggested.

Mode-locked flashlamp-pumped coumarin dye laser at 4600 Å

A flashlamp-pumped coumarin dye laser mode-locked by means of intracavity loss modulation has produced subnanosecond, millijoule pulses suitable for pumping other dye lasers or for application to fast photochemical reaction studies.