The laser plays an important role in high-resolution spectroscopy because of its high-powered output beam and narrow linewidth. The power range of the laser used can vary widely, from several milliwatts to several watts. The tuning range can cover wavelengths from the deep UV to the IR, and linewidths are available down to tens of kHz. Spectroscopists can choose from continuous wave (cw) or pulsed systems with pulsewidths as low as tens of femtoseconds.

There are a large number of high-resolution spectroscopic techniques, based on three broad principles. The laser wavelength can be tuned to an electronic absorption of the sample and the resulting fluorescence can be analyzed as a function of wavelength. Alternately, the instantaneous inelastic scattering of the sample, i.e. the Raman scattering, can be observed in vibrational spectroscopic techniques. Or, if laser excitation at an initial wavelength is introduced to a sample, absorption/transmission spectroscopy can be used to monitor the amount of light transmitted through the sample. If the excitation wavelength is scanned, an absorption spectrum can be analyzed. Many distinctions of this spectroscopy exist.

For cw applications, the most commonly used laser sources are the cw tunable systems in either dye or Ti:S configurations, pumped by other cw systems such as diode-pumped solid-state lasers (such as the Verdi Nd:YVO₄ system that provides single-frequency green output at 532 nm) or argon ion lasers (such as the Innova 300C). Narrow linewidth systems from Coherent are often employed in experiments because linewidth is an important factor in high-resolution spectroscopy. Most commonly the 899 Ring Lasers with linewidths between 500 kHz and 10 MHz are used (re: the 899-05, 899-21, and 899-29). Systems in a dye configuration typically cover the wavelength range between 375 nm and 1050 nm. The powers are high enough for these systems to allow efficient wavelength conversion through frequency doubling using the Model 8500 Frequency Doubler or the MBD-200 Frequency Doubler to the range from about 200 nm to 400 nm. Systems in a Ti:S configuration typically offer tunability in the range from 700 to 1000 nm, with frequency doubling capability as well. Because of the absence of any dye handling, the Ti:S laser has been accepted as a more hands-off and user-friendly laser. For applications that benefit from the Ti:S tuning range but demand even narrower linewidths and scanability, the MBR-110 Monolithic Block Resonator delivers robust performance with stabilized linewidths below 100 kHz.

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