Ultrafast 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 the 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 are 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 temporal width (duration) of the light pulses has to be on the same scale as the dynamics that are to be measured or even shorter. Ti-sapphire lasers are tunable lasers that emit red and near-infrared light (700 nm- 1100 nm).Ti-sapphire laser oscillators use Ti doped-sapphire crystals as a gain medium and Kerr-lens mode-locking to achieve sub-picosecond light pulses. Typical Ti:sapphire oscillator pulses have nJ energy and repetition rates 70-100 MHz. Chirped pulse amplification through regenerative amplification can be used to attain higher pulse energies. For amplification, laser pulses from the Ti:sapphire oscillator must first be stretched in time to prevent damage to optics, and then are injected into the cavity of another laser where pulses are amplified at a lower repetition rate. Regeneratively amplified pulses can be further amplified in a multi-pass amplifier. Following amplification, the pulses are recompressed to pulse widths similar to the original pulse widths. A dye laser is a four-level laser that uses an 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.