Wavelength-tunable lasers

There are several requirements for this to be a suitable deteetion method for a given moleeule. Obviously, tire moleeule must have a transition to a bound, exeited eleetronie state whose wavelength ean be reaehed with tunable laser radiation, and the band system must have been previously speetroseopioally assigned. If the moleeules are fonned with eonsiderable vibrational exeitation, the available speetroseopie data may not extend up to these vibrational levels. Transitions in the visible ean be aeeessed direetly by the output of a tunable dye laser, while transitions in the ultraviolet ean be reaehed by Ifequeney-doubled radiation. The... 

Laser Photochemistry. Photochemical appHcations of lasers generally employ tunable lasers which can be tuned to a specific absorption resonance of an atom or molecule (see Photochemical technology). Examples include the tunable dye laser in the ultraviolet, visible, and near-infrared portions of the spectmm the titanium-doped sapphire, Tfsapphire, laser in the visible and near infrared optical parametric oscillators in the visible and infrared and Line-tunable carbon dioxide lasers, which can be tuned with a wavelength-selective element to any of a large number of closely spaced lines in the infrared near 10 ]lni. 

The system used to measure the optical fiber signals employs two separate frequency tunable laser light sources operating at about 1320 nm wavelength. One laser acts as a pump laser, whereas the other serves as the probe laser that sends optical pulses down the fiber to interact with the counterpropagating laser light wave pumped into the fiber from its opposite end. 

The first, and still the most commonly used, of the tunable lasers were those based upon solutions of organic dyes. The first dye laser was developed by Sorokin and Lankard 05), and used a "chloro-aluminum phthalocyanine" (sic) solution. Tunable dye lasers operating throughout the visible spectrum were soon produced, using dyes such as coumarins, fluorescein, rhodamines, etc. Each dye will emit laser radiation which is continuously tunable over approximately the fluorescence wavelength range of the dye. 

Subsequent to the advent of the dye laser, tunable lasers based upon other lasing media were developed which operate over various wavelength ranges. Nobable among these are the f-center lasers and diode lasers which are tunable in the infrared. 

Additional laser diode technologies recently reported include a continuous-wave rhodamine 700 dye laser with a maximum wavelength output at 758 nm, powered by two laser diodes each operated with two standard AA batteries (RDT E division of the US Naval Command, Control, and Ocean Surveillance Center, San Diego, California), and a tunable laser diode with output laser wavelengths of 650, 780, 850, and 1320 nm (New Focus, Mountain View, California). 

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. 

Most optical spectral measurements, where the measurement of multiple wavelengths is required, will feature some type of polychromatic or broadband light source. There are a few exceptions here, such as tunable laser sources and source arrays. In such instances, the source is effectively "monochromatic at a given point in time. These sources are covered separately under monochromatic sources. 

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