Flash-lamp pumped laser dyes

Kaufmann and co-workersexplored several complementary methods to prepare 2,5-disubstituted oxazoles and 2,4,5-trisubstituted oxazoles as flash-lamp pumped laser dyes (Scheme 1.122). Prolonged reflux of 440 with POCI3 effected cyclodehydration to 5-(4-methoxyphenyl)-2-(4-pyridyl)oxazole 441 in modest... 

The condition for observing induced emission is that the population of the first singlet state Si is larger than that of So, which is far from the case at room temperature because of the Boltzmann distribution (see above). An inversion of population (i.e. NSi > Nso) is thus required. For a four-level system inversion can be achieved using optical pumping by an intense light source (flash lamps or lasers) dye lasers work in this way. Alternatively, electrical discharge in a gas (gas lasers, copper vapor lasers) can be used. 

The ICG was intravenously administered to 15 patients with CM at a total dose of 4 mg/kg b.w. Immediately after ICG injection, diode laser pulses with different radiant exposure (20-110 J/cm ) were applied as one single treatment. Five patients with extensive CM additionally received IPL (555-950 nm) therapy. Safety and efficacy were assessed at 1 and 3 months after the single treatment by a blinded investigator and the patient. Furthermore, coloxu- of the CM was objectively measured by means of a colour metre. Treatment with tire flash lamp-pumped pulsed dye laser (FPDL) and the IPL alone (five patients) served as the reference treatment. 

Figure 7.19 Principle of a flash-lamp pumped-dye laser. FL, flash lamp D, dye cell G, diffraction grating...

Experimental Setup. The instrumentation (both optics and electronics) for studying saturated laser induced fluorescence spectroscopy is much less conplicated than for CARS. The experimental setup shown in Figure 18, as used in our laboratory, is typical for these studies. In some experiments it is advantageous to use a monochromator rather than band pass filters to isolate the laser induced fluorescence signal. The lasers used are either flash lamp pumped systems or NdsYAG pumped dye lasers. 

Equation 31 is plotted in Figure 5 for typical combustion conditions and with the combined uncertainty in k. > ft and V as a parameter. The sample time is 1 Usee, typical of flash-lamp pumped dye laser pulses, and thus remarkably low detectability limits are achievable with single pulse sampling. 

From Figures 6, 18, and 20 we see that relative fluorescence measurements for OH, SH, S2, and SO along with the method for data reduction leads to reasonable agreement with the equilibrium expectations. In Figures 19 and 21 there is a somewhat wider spread of the data about the equilibrium expectation. This is probably caused by the use of non-optimal measuring conditions and data reduction for S02 which has a very complex spectrum at flame temperatures. We are expecting a Nd-Yag laser shortly which will operate deeper into the UV than our present flash lamp pumped dye laser and will permit a more extensive characterization of SO2 fluorescence in the flame environment. 

Dye laser A CW or pulsed source of coherent radiation in which the active medium is usually a solution of a fluorescent organic molecule (the dye) pumped with a suitable pump laser or with a flash lamp. These lasers can be tuned over a large part of the fluorescence band of the dye. 

The excitation spectra of marine phytoplankton were found to be broad (6). Considering this feature, we emphasized continuous and rapid measurement at discrete excitation wavelengths. Flash-lamp pumped dye lasers were used because of their simplicity and their high efficiency. The excitation wavelengths were at 457, 499, 536, and 578 nm. 

Schlieren photographs of the spark kernel and the developing flame were obtained using a conventional arrangement. A flash-lamp-pumped dye laser was used to furnish a 1 ys light pulse (X 600 nm) to illuminate the interior of the combustion bomb. 

G. Marowsky A tunable flash lamp pumped dye ring laser of extremely narrow bandwidth. IEEE J. QE-9, 245 (1973)... 

In order to detect the intensity change of one mode in the presence of many others, the laser output has to be dispersed by a monochromator or an interferometer. The absorbing molecules may have many absorption lines within the broad-band gain profile of a multimode dye laser. Those laser modes which overlap with absorption lines are attenuated or even completely quenched. This results in "spectral holes" in the output spectrum of the laser and allows the sensitive simultaneous recording of the whole absorption spectrum within the laser bandwidth, if the laser output is photographically recorded behind a spectrograph. ATKINSON et al. [8.17] demonstrated this technique by monitoring with a flash lamp-pumped dye laser the time-dependent concentration of the short-lived radicals NH2 and HCO which had been formed by flash photolysis of NH. ... 

The common liquid lasers utilize a flowing dye as the active medium and are pumped by a flash lamp or another laser. These are typically more complex systems requiring more maintenance. They can he operated as either CW (continuous wave) or pulsed. One advantage liquid lasers have is they can be tuned for different wavelengths over a 100-nm range. 

The necessary pump powers can be achieved either by other lasers (e.g. nitrogen lasers, solid-state lasers or even focussed He-Ne- or Ar+-gas lasers) or by flash-lamps. The simplest practical arrangement is a square spectrophotometer cell, polished on all sides, containing the dye solution which is pumped by a nitrogen laser whose beam is focussed into a line parallel to and directly behind one of the cell windows. Then the Fresnel reflection from the two adjacent windows gives enough feedback in most cases, so that no additional resonator mirrors are needed and the dye laser oscillation starts. 

A pulsed dye laser pumped with flash lamps is used in most cases, as here the selection of different dyes, frequency doubling and Raman shifting, which is possible as a result of the high energies available, allows the whole spectral range down to 200 nm to be covered. However, diode lasers, particularly for multistep excitation, and dye lasers pumped with an excimer or a nitrogen laser can also be applied. 

Depending on the pumping source (either flash-lamps or other laser systems, such as excimer, Nd YAG, nitrogen, or copper vapor lasers), the repetition rate of the dye laser can be varied between 10Hz and as high as a megahertz. It is obvious that at low repetition rates only a small fraction of analyte atoms, which pass the interaction volume, is irradiated by the laser. This restricts the detection limit of the measurement, in particular if only small amounts of sample material are available, as in microanalysis. 

---