Basics of Laser Physics For Students of Science and Engineering
Basics of Laser Physics provides an introductory presentation of the field of all types of lasers. It contains a general description of the laser, a theoretical treatment and a characterization of its operation as it deals with gas, solid state, free
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Introduction
We will ask and partly answer a few questions. What is the difference between a laser and a light bulb? In which frequency ranges are lasers available? Which are the sizes and the costs of lasers? Why is it necessary to have different types of lasers in the same frequency range? We will also mention some specific lasers and we will discuss the concept of the book.
1.1 Laser and Light Bulb The spatial and temporal coherence makes the difference between a laser and a light bulb (Fig. 1.1). While a lamp emits uncorrelated wave trains into all spatial directions, a laser generates coherent waves and the waves can have a high directionality. Which are the possibilities of generation of spatially and temporally coherent waves? A laser can generate a coherent continuous wave or a coherent pulse train. Extreme cases of generation of visible radiation are as follows: • The continuous wave laser (cw laser) emits a continuous electromagnetic wave. The field is spatially and temporally coherent. • The femtosecond laser emits an electromagnetic wave consisting of a pulse train; the duration of a single pulse of a train can be as short as 5 fs (1 fs D 1 femtosecond D 1015 s). The field of a pulse train is spatially and temporally coherent too. Beside continuous wave lasers and femtosecond lasers, there are pulsed lasers producing laser pulses with durations in the picosecond, nanosecond, microsecond, or millisecond ranges. We use the abbreviations: • • • •
1 ms D 1 millisecond D 103 s 1 s D 1 microsecond D 106 s 1 ns D 1 nanosecond D 109 s 1 ps D 1 picosecond D 1012 s
K.F. Renk, Basics of Laser Physics, Graduate Texts in Physics, DOI 10.1007/978-3-642-23565-8 1, © Springer-Verlag Berlin Heidelberg 2012
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1 Introduction
Fig. 1.1 Continuous wave (cw) laser, femtosecond (fs) laser and light bulb
• 1 fs D 1 femtosecond D 1015 s • 1 as D 1 attosecond D 1018 s The acronym LASER means: Light Amplification by Stimulated Emission of Radiation. It developed to laser D device for generation of coherent electromagnetic waves by stimulated emission of radiation. The maser (Dmicrowave laser) makes use of microwave amplification by stimulated emission of radiation.
1.2 Spectral Ranges of Lasers and List of a Few Lasers Figure 1.2 shows wavelengths and frequencies of spectral ranges of the electromagnetic spectrum — from X-rays over the ultraviolet (UV), the visible, the near infrared (NIR), the far infrared (FIR) spectral ranges to microwaves and radiowaves. The frequency of an electromagnetic wave in vacuum obeys the relation D c=;
(1.1)
where c (D 3 108 m s1 ) is the speed of light and the wavelength. Abbreviations of frequencies are as follows: • • • •
1 MHz D 1 megahertz D 106 Hz 1 GHz D 1 gigahertz D 109 Hz 1 THz D 1 terahertz D 1012 Hz 1 PHz D 1 petahertz D 1015 Hz
The visible spectral range corresponds to a frequency range of about 430–750 THz (wavelength range about 400–700 nm). Optics and light refer to electromagnetic waves with vacuum wavelengths smaller than about 1 mm, i.e., with fre
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