**Introduction**

**Chapter 1**

© 2012 Peshko, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

This book is devoted to Laser Pulses. In the modern laser world, the word "Pulse" covers pulse durations from microseconds (free-running laser) to tens of femtoseconds (1fs is 10-15 s) (mode-locked laser). It is possible to generate attosecond pulses (1as is 10-18 s) by using nonlinear processes. Recently, a new time range was discussed in publications: zeptosecond (1zs is 10-21 s). To generate pulses from milliseconds to femtoseconds, hundreds of different laser systems have been developed. They can typically generate pulses of specific durations, which are due to laser principles of operation, specific construction, parameters of gain

In the solid-state free-running laser the parameters of the electromagnetic field interaction process with an inversed population of the gain medium play a dominant role in shaping the laser spikes. These characteristic parameters limit the pulse duration from the long side of the range. A chaotic sequence of such spikes can be as long as the pumping source could effectively excite the gain medium. In some technological applications this can be hundreds of milliseconds envelop. To achieve laser pulse duration of a few seconds, it is necessary to use for modulation the processes with characteristic times of the same order of magnitude. On the short side of achievable durations, another limitation exists. At certain conditions, waves, interacting with solids, can shape a single peak of energy, propagating "alone". In optics, such a single wave is called a "soliton". A tsunami is an example of a mechanical soliton. To propagate in a crystal, an "optical tsunami" can excite the medium and get back the energy at some conditions. In a vacuum, there is no medium that can accumulate energy and support existence of a relatively short, lossless wave. Hence, in a vacuum, a single pulse could be shaped as a wave-package, which is a result of interference of many independent electromagnetic waves, propagating co-axially in the same direction. Since light is an electromagnetic wave repeatable in space and time, a single wave period with minimal

**Time and Light** 

http://dx.doi.org/10.5772/54208

**1.1. From seconds to attoseconds** 

medium, type of modulator, and so on.

**1. Introduction** 

Additional information is available at the end of the chapter

Igor Peshko

**Chapter 1**
