ABSTRACT
The 1990s brought about dramatic advances in controlling ultrashort-pulse optical radiation. The quest for ever shorter laser pulses led to pulse durations as short as approximately twice the oscillation period of the carrier field (T0 ≈2.6 fs at λ0=0.8 µm, the center wavelength of the titaniumdoped sapphire laser), approaching the limit set by the laser cycle (Cheng et al., 1998; Baltuska et al., 1997; Morgner et al., 1999; Sutter et al., 1999). Furthermore, the frequency sweep (chirp) and amplitude envelope of femtosecond pulses can now be tailored (e.g., Weiner, 2000) for specific applications, such as coherent control of molecular dynamics, often referred to as femtochemistry (Judson and Rabitz, 1992). Recently it was demonstrated that techniques similar to those used for controlling chemical reactions can also be efficiently employed for influencing products of strong-field interactions, such as high-harmonic radiation (Bartels et al., 2000). This process, if driven by few-cycle pulses (Spielmann et al., 1997; Schnürer et al., 1998), is capable of delivering X-ray pulses shorter than the oscillation period of the driving laser (Drescher et al., 2001) and has the potential to produce pulses shorter than 1 fs in duration (e.g., Brabec and Krausz, 2000). The parameters of pulses near 1 fs and possibly attosecond pulses emerging from this process have been predicted to sensitively depend on how the oscillations of the electric field
fit within the amplitude envelope (de Bohan et al., 1998; Tempea et al., 1999). This is determined by φ, which has been referred to as the absolute or carrier envelope phase of light pulses (Xu et al., 1996). This parameter, which could not be accessed experimentally until recently, is the focus of this chapter. Its control and measurement in femtosecond pulses will have dramatic impacts on frequency domain and time domain metrology alike.
