Ultra fast laser spectroscopy

Ultrafast laser spectroscopy is a spectroscopic technique that uses ultrashort pulse lasers for the study of dynamics on extremely short time scales (attoseconds to nanoseconds). Different methods are used to examine dynamics of charge carriers, atoms and molecules. Many different procedures have been developed spanning different time scales and photon energy ranges; some common methods are listed below.

Dynamics on the as to fs time scale is in general too fast to be measured electronically. Most measurements are done by employing a sequence of ultrashort light pulses to initiate a process and record its dynamics. The width of the light pulses have to be on the same scale as the dynamics that is to be measured.

Ti-sapphire lasers are tunable lasers which emit red and near-infrared light (700 nm- 1100 nm).Ti-sapphire laser systems use Ti-sapphire as a gain medium. The pulses will go into a stretcher where the pulse duration is stretched, and then to a regenerate amplifier, where the pulse energy is amplified. The output pulses from the regenerate amplifier are further sent to a multi-pass amplifier, where the pulses can be amplified to even higher energies. The pulses from either the regenerate amplifier or the multi-pass amplifier are sent to a compressor, where the pulse duration is compressed.

A dye laser is a four-level laser which uses organic dye as the gain medium. Pumped by a laser with a fixed wavelength, due to various dye types you use, different dye lasers can emit beams with different wavelengths. A ring laser design is most often used in a dye laser system. Also, tuning elements, such as a diffraction grating or prism, are usually incorporated in the cavity. This allows only light in a very narrow frequency range to resonate in the cavity and be emitted as laser emission. The wide tuneability range, high output power, and pulsed or CW operation make the dye laser particularly useful in many physical & chemical studies.

A fiber laser is usually generated first from a laser diode. The laser diode then couples the light into a fiber where it will be confined. Different wavelengths can be achieved with the use of doped fiber. The pump light from the laser diode will excite a state in the doped fiber which can then drop in energy causing a specific wavelength to be emitted. This wavelength may be different from that of the pump light and more useful for a particular experiment.

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