Types of Dye Lasers

In this section the types of dye lasers, the mechanism of lasing as applied to dyes, structural types of laser dyes and a few of the applications of dye lasers will be dis-cussed.  

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FIGURE 1 The historical (development of the three main types of (dye lasers used as scientific instruments today. The year of introduction in the literature is shown of ideas discussed in this text, along with an indication of the types of pump lasers predominately in use and the output specifications available from each type of dye laser. 

We now present the most important types of dye lasers in practical use for high-resolution spectroscopy. 

Reaction with vatious nucleophilic reagents provides several types of dyes. Those with simple chromophores include the hernicyanine iodide [16384-23-9] (20) in which one of the terminal nitrogens is nonheterocyclic enamine triearbocyanine iodide [16384-24-0] (21) useful as a laser dye and the merocyanine [32634-47-2] (22). More complex polynuclear dyes from reagents with more than one reactive site include the trinuclear BAB (Basic-Acidic-Basic) dye [66037-42-1] (23) containing basic-acidic-basic heterocycles. Indolizinium quaternary salts (24), derived from reaction of diphenylcyclopropenone [886-38-4] and 4-picoline [108-89-4] provide trimethine dyes such as (25), which absorb near 950 nm in the infrared (23). 

Dye lasers have been one of the most widely used types of tunable laser. In pulsed conditions, typical peak powers are in the range of 10 -10 W. In the cw regime, reported powers are in the order of watts, with linewidths of around 1 MHz. Due to their flexibility in design and performance, dye lasers have been commonly used in a great variety of spectroscopic techniques, including high-resolution spectroscopy. 

Tunable coherent light sources can be realized in several ways. One possibility is to make use of lasers that offer a large spectral gain profile. In this case, wavelength-selecting elements inside the laser resonator restrict the laser oscillation to a narrow spectral interval and the laser wavelength may be continuously tuned across the gain profile. Examples of this type of tunable laser are the dye lasers were treated in the previous section. 

The main advantages of dye lasers are spectrum coverage (from less than 400 to 1000 nm) and tunability. In general, the laser dyes used nowadays have changed little from those used a decade ago [3]. Coumarins such as (73) and xanthenes such as Rhodamine 6G (74), are the main types. However, fluorinated coumarin dyes such as (75) have higher light stability than their nonfluorinated counterparts [39],... 

The majority (in numbers) of dye lasers in existence is represented by the three scientific types already discussed, but these by no means represent the diversity of ways that lasers with a dye gain medium have been built. In this concluding section, four additional dye lasers are briefly discussed as a better indication of the breadth of this laser type and of its potential impact on future technology. 

As the name implies, the active medium of dye lasers comprises organic dyes. The way the active medium is presented to the laser is radically different from other types of laser, in that the organic dye is incorporated in a hquid solvent. The dye solution used in dye lasers typically has a concentration in the range 10 2-10 4moll... 

Visualization, documentation, and analysis of the results are very important aspects of each experiment. Commercially available gel documentation systems are equipped with various types of detection methods and software. Depending on the type of dye, several devices can be used, such as scanners, CCD cameras, illuminators with UV or white light, fluorescent imagers, and laser densitometers. For each image system, there is compatible software for processing and evaluation of the results and for data documentation. 

The efficiency of energy conversion of the pumping laser radiation in commercially available lasers varies from a few percent to ca. 20%. depending on the type of dye and the spectral range. 

We would like to note that the designing of tunable diode lasers is one of the most promising approaches used for the development of gas analyzers aimed for detection of a spedlic gas (Somesfalean et al. 2005). Gas analyzers based on tunable diode lasers are considerably simpler in comparison with conventional systems. A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. There are many types and categories of tunable lasers. They exist in the gas, liquid, and solid slates. Among the types of tunable lasers are excimer lasers, COj lasers, dye lasers (liquid and solid slate), transition-metal solid-state lasers, semiconductor crystal and diode lasers, and free-electron lasers (Duarte 1995). 

In the visible range dye lasers in their various modifications are by far the most widely used types of tunable lasers. Their active media are organic dye molecules solved in liquids, which display strong broad-band fluorescence spectra under excitation by visible or uv light. With different dyes the overall spectral range, where cw or pulsed laser operation has been achieved, extends from 300 nm to 1.2 ym. In this section we briefly summarize the basic physical background and the most important experimental realizations of dye lasers, used in high-resolution spectroscopy. For a more extensive treatment the reader is referred to the laser literature (e.g., [7.31,32b]). 

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