Ultrashort pulse

Ultrashort Pulse

An ultrashort pulse is a light pulse with a duration on the order of picoseconds (10^-12 seconds) or femtoseconds (10^-15 seconds). These pulses are typically generated by mode-locked lasers and are used in a variety of scientific and industrial applications due to their extremely short duration and high peak intensity.

Diagram illustrating the characteristics of an ultrashort pulse.

Generation

Ultrashort pulses are commonly generated using mode-locking techniques in lasers. Mode-locking is a process that forces the phases of different frequency modes of a laser to lock together, resulting in the emission of a pulse of light that is much shorter than the continuous wave output of the laser. There are several types of mode-locking, including active, passive, and hybrid techniques.

Active Mode-Locking

Active mode-locking involves the use of an external modulator to periodically modulate the loss or the phase of the laser cavity. This modulation synchronizes the phases of the different modes, leading to the generation of short pulses.

Passive Mode-Locking

Passive mode-locking uses a saturable absorber, a material whose absorption decreases with increasing light intensity, to achieve mode-locking. As the intensity of the light in the laser cavity increases, the saturable absorber becomes transparent, allowing the formation of a short pulse.

Applications

Ultrashort pulses have a wide range of applications in science and technology. They are used in time-resolved spectroscopy to study fast processes in chemistry and biology. In material science, they are used for micromachining and laser ablation. Ultrashort pulses are also crucial in the field of optical communications and nonlinear optics.

Measurement

Measuring ultrashort pulses requires specialized techniques due to their extremely short duration. Common methods include autocorrelation and frequency-resolved optical gating (FROG). These techniques allow researchers to determine the pulse duration and shape, which are critical for many applications.

Related Pages

• Mode-locking
• Femtosecond laser
• Nonlinear optics
• Time-resolved spectroscopy

References

• Agrawal, G. P. (2001). Nonlinear Fiber Optics. Academic Press.
• Keller, U. (2003). "Recent developments in compact ultrafast lasers". Nature. 424: 831–838.
• Moulton, P. F. (1986). "Spectroscopic and laser characteristics of Ti:Al2O3". Journal of the Optical Society of America B. 3 (1): 125–133.