Fluorescence solid-state lasers

Advances in laser technology now allow for solid-state lasers of high beam quality. These beams may be projected from a much smaller auxiliary telescope, which negates the need for optical switching and completely eliminates any main telescope fluorescence. Solid-state YAG lasers are the most common type of lasers commercially available. These lasers use a crystal as the lasing... 

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). 

The choice of sensor material determines range, sensitivity, and stability. By considering the latter factors, it is found that inorganic insulating compounds, such as most lamp phosphors and many solid state laser materials, are the most suitable materials for thermometric applications. Indeed, these materials are most commonly used in the existing commercial fluorescence thermometer schemes. 

The yttrium aluminum garnet crystal, Y3 AI5O12, doped withNd + ions, is a well-known solid state laser material (abbreviated to Nd YAG). If the fluorescence lifetime of the main laser emission is 230 /rs and the quantum efficiency of the corresponding emitting level is 0.9, determine (a) the radiative lifetime and... 

The fluorescence lifetime, r, of Nd + in Ca3Ga2Ge30i2 crystal (a solid state laser) is measured as a function of the neodymium concentration, Cnij, giving... 

In the previous chapter we have introduced the physical basis of the interpretation of optical spectra of centers in crystals. The main effect of these centers is to introduce new energy levels within the energy gap of the crystal, so that the transitions among these levels produce new optical bands that are not present in the perfect crystal. Due to these absorption and emission bands, centers in crystals are relevant for a variety of applications, such as solid state lasers, amplifiers and phosphors for fluorescent lighting and cathode ray tubes. In this chapter, we will describe the main characteristics of the relevant centers for these applications. 

The fluorescence lifetime of the /2 metastable state of Nd + ions in LaBGeOs (a solid state laser) is 280 /u.s and its quantum efficiency is 0.9. (a) Calculate the radiative and nonradiative rates from this excited state, (b) If the effective phonons responsible for the nonradiative rate have an energy of 1100 cm, use the Dieke diagram to determine the number of emitted effective phonons from the F3/2 excited state, (c) From which three excited states of the Nd + ions in LaBGeOs do you expect the most intense luminescence emissions to be generated ... 

In solid state lasers the fluorescence lines are broadened 26) by statistical Stark fields of the thermal vibrating crystal lattice and furthermore by optical inhomogenities of the crystal. The corresponding laser lines are accordinglyjlarge at multimode operation 22)... 

Most of the solid-state lasers employ as active material crystals or glasses doped with rare-earth or actinide ions, because these ions exhibit a large number of relatively sharp fluorescent lines, covering the whole visible and near-infrared spectrum 380) search for new laser materials and investigations of the characteristics of laser emission at different temperatures of the active material and with various pump sources have improved knowledge about the solid state spectra and radiationless transitions in laser media 38i). 

Photochemical Stability and the Wavelength of Excitation. Cyanines of chain length beyond Cy3 snffer from increasing photochemical instability. This can be a problem when they are nsed in conjunction with solid-state lasers operating around 630-650 nm. To overcome these problems workers at Boehringer Mannheim have developed the so-called pentacyclic fluorescent labels based on either the oxazine or rhodamine ring systems, e.g. Light Cycler Red 640 NHS (3.76). ... 

Laser dye/Si02 gel CT AB/decanol/decane/ formamide (nonaqueous xE) TE0S/H20 (pH 1, HNO 3 10-2 M laser dye) Silica gels doped with laser dyes (rhodamine B, rhodamine 6G) gave fluorescence quantum yields indicating promise as candidate solid-state laser dye materials (49)... 

Applications making use of the nonlinear absorption of dyes are passive Q-switching in solid-state lasers, pulse shaping, pulse intensity measurements of high-power ultrashort pulses, optical isolation between amplifier stages of high power solid-state lasers, and pulse width measurements of ultrashort pulses by the two-photon-fluorescence (TPF) method. 

One drawback of dye lasers as compared to solid-state lasers is the short fluorescence lifetime rp or energy storage time, which implies a quick inversion decay when pumping stops. For this reason one cannot Q-switch a dye laser. On the other hand, dye lasers can be mode-locked by saturable absorbers 52> in much the same way as solid-state lasers, and many investigations have shown that one can obtain psec pulse in this way over a wide spectral region 53,54)... 

Femtosecond Ti-Sapphire oscillator (CDP, TiF50, 100 fs, 80 MHz, 0.3 W, 800 run) pumped with diode pumped solid state laser (Coherent, Verdi) was used to excite the system. The time- and spectral-resolved fluorescence spectra of C522 were measured by using up-conversion set-up (CDP, FOG100). The p-cyclodextrin, C42H70O35, and coumarin C522, C14H12F3NO2, used in these experiments were produced by Cyclolab and Radiant Dyes Chemie, respectively. All experiments were performed at room temperature and used water was twice deionised. 

The prism at the outlet of the laser serves to separate the laser emission of the gas fluorescence and allows for a clean excitation of the sample. For excitation using solid-state lasers, this element is dispensable. The lens (element 5) collects the fluorescent signal and focuses on the aperture of the monochromator. The filter is used to eliminate excitation that is spread over the surface of the sample. The optical chopper serves to modulate the light at a defined frequency, which serves as reference for the lock-in amplifier. A data acquisition system controls the pace of the monochromator and reads the signal of the lock-in, generating the sample s emission spectrum. 

The most widely used solid-state laser is Nd YAG. The properties and operating characteristics of this laser have been thoroughly reviewed by Darnelmeyer (51). All fluorescence transitions from Tto the states have lased in YAG. Cooling lowers the threshold for the - i transitions ... 

Robbins et al. on tryptophan and 3-methylindole since powerful solid-state laser excitation was used. Jameson and Weber have resolved the fluorescence of tryptophan by phase and modulation fluorometry in terms of emission from the zwitterion and anion present in amounts determined by the pH of the solution. The forms interconvert more slowly than fluorescence processes and have similar absorption and emission spectra. Measurements were made with excitation frequencies of 6, 18, and 30 MHz in the pH range 8—10, in which the relative zwitterion concentration varies from 0.82—0.09. Resolved lifetimes were 3.1 0.4 ns for the zwitterion and 8.7 0.1 ns for the anion. The agreement with Gudgin et al. seems satisfactory. 

Trivalent europium has been demonstrated to produce a bright red fluorescence, which peaks at about 615 nm in glasses. More recently, europium was successfully incorporated into gel-derived glasses [33,34]. Possible applications include solid-state lasers in the visible and fiber-optic amplifiers. The fluorescence spectra of Eu3+-doped silica is presented in Fig. 5. The 615 nm peak associated with the 5Do transition state is clearly evident, along with three... 

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