Ultrashort Laser Pulses Applications

Abstract

Ultrashort laser pulses are considered to be pulses of electromagnetic radiation whose duration is shorter than the thermal vibration period of molecules, around tens of picoseconds (10-12 s). Pulses with durations of a few picoseconds were already produced in the 1960’s (DiDomenico et al., 1966), shortly after the laser invention, using the mode-locking technique (Hargrove et al., 1964; Haus, 2000). In the next decade, refinements on this pulse generation scheme, and the use of bulky dye lasers with large emission bandwidths, shortened the pulses to the hundreds of femtoseconds (10-15 s) timescale (Diels et al., 1978; Shank & Ippen, 1974). In the 1980’s, pulses with durations below 10 femtoseconds were generated from dye lasers (Fork et al., 1987; Knox et al., 1985), however the applications had to wait for the Ti:Sapphire KerrLens mode-locked laser (Brabec et al., 1992; Spence et al., 1991) and the Chirped Pulse Amplification (CPA) technique (Strickland & Mourou, 1985) to really spread out. The large Kerr effect and broad emission bandwidth available in the Ti:Sapphire (Moulton, 1986), and the diode pumped solid state lasers (Keller, 1994; Keller, 2010; Scheps, 2002) that became available around this time, greatly simplified the setup needed to generate ultrashort pulses, and promptly replaced the dye lasers for this purpose. Finally, the invention of the CPA technique in 1985, allowed the generation of high intensity ultrashort pulses in all-solid state laser systems, and disseminated these laser systems due to its simplicity of operation when compared to the preceding systems, stability and relatively low cost. The CPA technique (Diels & Rudolph, 2006; Maine et al., 1988; Mourou et al., 1998) consists in generating ultrashort pulses with nanojoules of energy in a main oscillator laser, then temporally stretching these pulses by chirping its frequency (dispersion control) (Rulliere, 1998) to decrease its power and intensity, allowing its amplification up to more than a million times without damaging the amplification chain components; after the amplification, the pulses are compressed to durations close to their original ones and directed to the applications. When the CPA technique became prominent, the pulses stretching and compression were mainly done with diffraction gratings (Fork et al., 1984; Martinez, 1987a; Martinez, 1987b; Treacy, 1969), although nowadays other techniques are disseminated, such as the use of Chirped Mirrors (Nisoli et al., 1997; Szipocs et al., 1994), fiber stretchers (Zhou et al., 2005) and prisms and grisms compressors (Chauhan et al., 2010). As the years went by, scientific and technological developments led to the dissemination of ultrashort pulses systems based in other mode-locking schemes such as SESAMs (Semiconductor Saturable Absorber Mirrors) (Keller, 2010) and gain media including