Fluorescence ruby laser

Lasers produce spatially narrow and very intense beams of radiation, and lately have become very important sources for use in the UV/VIS and IR regions of the spectrum. Dye lasers (with a fluorescent organic dye as the active substance) can be tuned over a wavelength range of, for instance, 20-50 nm. Typical solid-state lasers are the ruby laser (0.05% Cr/Al203 694.3 nm) and the Nd YAG laser (Nd3+ in an yttrium aluminium garnet host 1.06 pm). 

Cr + ions in aluminum oxide (the ruby laser) show a sharp emission (the so-called Ri emission line) at 694.3 nm. To a good approximation, the shape of this emission is Lorentzian, with Av = 330 GHz at room temperature, (a) Provided that the measured peak transition cross section is c = 2.5 x 10 ° cm and the refractive index is = 1.76, use the formula demonstrated in the previous exercise to estimate the radiative lifetime, (b) Since the measured room temperature fluorescence lifetime is 3 ms, determine the quantum efficiency for this laser material. 

Using as the background continuum the short-lived spontaneous fluorescence of rhodamine B or 6 G, McLaren and Stoicheff 233) developed this method further to obtain inverse Raman spectra over the range of frequency shifts 300-3500 cm" in liquids and solids in a time of 40 nsec The stimulating monochromatic radiation at 6940 A is provided by a giant-pulse ruby laser. A small part of the main laser beam is frequency-doubled in a KDP-crystal and serves to excite the rhodamine fluorescence, thus ensuring simultaneous irradiation of the sample by both beams. 

A novel, short-lived (< 10 sec) visible luminescence has been observed when dibenzothiophene is excited by an unfocused ruby laser. The luminescence occurs throughout the visible region and bears no resemblance to either normal fluorescence or phosphorescence. It is thought that a molecular fragmentation is involved which is followed by a chemiluminescent emission. 

Very broadly speaking, two situations have to be considered in explaining devices such as those we have mentioned. In the first, which is relevant to the ruby laser and to phosphors for fluorescent lights, the light is emitted by an impurity ion in a host lattice. We are concerned here with what is essentially an atomic spectrum modified by the lattice. In the second case, which applies to LEDs and the gallium arsenide laser, the optical properties of the delocalised electrons in the bulk solid are important. 

Many aryl-substituted pyrylium salts are intensely fluorescent. It is possible to predict these spectral properties by a consideration of the shape of the molecule, the nature of substituents and the length of the ir-electron system (75MI22203). Pyrylium salts have been used as Q-switches for neodymium and ruby lasers in acetonitrile (68MI22200). 

Absorption spectra were recorded in a Perkin-Elmer spectrophotometer, and fluorescence spectra were recorded on a Perkin-Elmer Ul+B spectrofluorimeter. Flash photolysis studies were carried out using an excimer laser, X excitation = 3080A°, a ruby laser, X excitation = 3 71A°, or a nitrogen laser, X excitation = 3391A°. The system has been described previously. 

Thus, it has been studied azoethane decomposition [21] stimulated by ruby laser (/.=694.3nm) with power density equal to 70+175 MW/cm2. It has been established that the N2 yield is proportional to the order 2.2 0.1 with respect to the light intensity. The authors of [22] suppose that after photon absorption the excited molecules from the first excited singlet state A are transfered to an other excited singlet state B from which fluorescence is forbidden. The both states are at close range. The excited molecules which are on B level may be decomposed with a rate which depends on the nature of radicals linked with azo group. The authors of [23] assume that both mechanisms (thermo-and photo) are identic, but only in the case of photolysis transfer to triplet (T) state is possible. 

In some favorable cases TPE was efficient enough to form measurable amounts of photodecomposition products. Examples are the dissociation of iodoform by a ruby laser s and of water by a doubled dye laser. In the first, the reaction was followed by titrating the liberated iodine, while in the second, OH radicals were monitored by laser-induced fluorescence, using the same laser frequency for both two-photon dissociation of HjO and one-photon fluorescence excitation of OH. 

Continuous emission from NOa 359 and single vibronic level fluorescence from NOa 360 have been reported. The lifetimes of the 2Bl K > 0) states were measured, and the interesting result was obtained that the lifetime of the K = 4, N = 16 1 level was 36 [xs, substantially greater than that of the K = 0 levels. The increase in lifetime is attributed to Renner interaction of the and 2AX components of the linear 2 state. Rotational excitation has been shown to assist in the dissociation of NOa in the 249.1 nm system, but this is minor in extent compared with that observed in the 397.9 nm system. Yields of 0(4)) were reported.361 The photolysis of NOa has been further studied.362 In the report by Harteck et al., a two-photon excitation process was observed when a pulsed ruby laser was used for excitation. Thermal and photochemical reactions of NOa with butyraldehyde,363 other aldehyde-NO systems,364 and methylperoxyl radical-NOx reactions 365 have been discussed. 

In 1961, Kaiser and Garrett (1961) illuminated CaFjiEu crystals with the red light of a ruby laser and observed fluorescence in the blue The absence of any... 

In the collinear arrangement the anti-Stokes wave at = 2o)i-(<)2 (w > Wj ) is detected through filters which reject both incident laser beams and also the fluorescence which may be generated in the sample. Figure 8.12 illustrates a typical experimental setup used for rotational-vibrational spectroscopy of gases by CARS [8.50]. The two incident laser beams are provided by a Q-switched ruby laser and a tunable dye laser, pumped by this ruby laser. Because the gain of the anti-Stokes wave depends quadratically on the molecular density N, see (8.33), high power levels of the incident... 

Figure 11. Schematic representation of a laser heating experiment in the DAC. The IR laser beam is directed onto the absorbing sample immersed in a compression medium acting also as thermal insulator. The thermal emission of the sample is employed for the temperature measurement, while the local pressure is obtained by the ruby fluorescence technique (see next section).

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