About Laser


The Extreme Light Infrastructure for Nuclear Physics (ELI-NP) project in Romania has recently reached a significant milestone: the ultra-high intensity laser system developed by Thales has successfully generated its first pulses at a peak power level of 10 petawatts (1015 W).

They're many type of lasers. The main are diode laser, solid state laser, CO2 laser, fiber laser. Most of the laser pointers are diode laser, while CO2 laser are used for laser cutting,engraving, marking. The fiber laser can be very high output. The DPSS laser here are the solid state laser. 

Introduction to How Lasers Work
Lasers show up in an amazing range of products and technologies. You will find them in everything from CD players to dental drills to high-speed metal cutting machines to measuring systems. They all use lasers. But what is a laser? And what makes a laser beam different from the beam of a flashlight?

Laser light is very different from normal light. Laser light has the following properties:

  • The light released is monochromatic. It contains one specific wavelength of light (one specific color). The wavelength of light is determined by the amount of energy released when the electron drops to a lower orbit.
  • The light released is coherent. It is “organized” -- each photon moves in step with the others. This means that all of the photons have wave fronts that launch in unison.
  • The light is very directional. A laser light has a very tight beam and is very strong and concentrated. A flashlight, on the other hand, releases light in many directions, and the light is very weak and diffuse.

To make these three properties occur takes something called stimulated emission. This does not occur in your ordinary flashlight -- in a flashlight, all of the atoms release their photons randomly. In stimulated emission, photon emission is organized.

The photon that any atom releases has a certain wavelength that is dependent on the energy difference between the excited state and the ground state. If this photon (possessing a certain energy and phase) should encounter another atom that has an electron in the same excited state, stimulated emission can occur. The first photon can stimulate or induce atomic emission such that the subsequent emitted photon (from the second atom) vibrates with the same frequency and direction as the incoming photon.

The other key to a laser is a pair of mirrors, one at each end of the lasing medium. Photons, with a very specific wavelength and phase, reflect off the mirrors to travel back and forth through the lasing medium. In the process, they stimulate other electrons to make the downward energy jump and can cause the emission of more photons of the same wavelength and phase. A cascade effect occurs, and soon we have propagated many, many photons of the same wavelength and phase. The mirror at one end of the laser is "half-silvered," meaning it reflects some light and lets some light through. The light that makes it through is the laser light.

You can see all of these components in the figures on the following page, which illustrate how a simple ruby laser works.

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Describe how a laser works.

Laser Classification

Lasers have been classified by wavelength and maximum output power. We devided them into four classes and a few subclasses since the early 1970s. The classifications categorize lasers according to their ability to produce damage in exposed people, from class 1 (no hazard during normal use) to class 4 (severe hazard for eyes and skin). There are two classification systems, the "old system" used before 2002, and the "revised system" being phased in since 2002. 

Revised system

The main characteristics and requirements for the classification system as specified by the IEC 60825-1 standard are listed, along with typical required warning labels.

Class 1

A Class 1 laser is safe under all conditions of normal use. This means the maximum permissible exposure (MPE) cannot be exceeded, when viewing a laser with the naked eye or with the aid of typical magnifying optics (e.g. telescope or microscope).

Class 1M

A Class 1M laser is safe for all conditions of use, except when passed through magnifying optics, such as microscopes and telescopes. 

Class 2

A Class 2 laser is safe, because the blink reflex will limit the exposure to no more than 0.25 seconds.

Class 2M

A Class 2M laser is safe because of the blink reflex, if not viewed through optical instruments. As with class 1M, this applies to laser beams with a large diameter or large divergence, for which the amount of light passing through the pupil cannot exceed the limits for class 2.

Class 3R

A Class 3R laser is safe if handled carefully. With a class 3R laser, the MPE can be exceeded, but with a low risk of injury. Visible continuous lasers in Class 3R are limited to 5 mW. 

Class 3B

A Class 3B laser is hazardous if eyes are exposed directly. Diffuse reflections, such as those from paper or other matte surfaces are not harmful.

Class 4

Class 4 is the highest and most dangerous class of lasers, including all lasers that exceed the Class 3B AEL. 

Old system

The safety classes in the "old system" of classification were established in the United States through consensus standards (ANSI Z136.1) and Federal and state regulations.

Class I

Inherently safe; no possibility of eye damage. This can be either because of a low output power (in which case eye damage is impossible even after hours of exposure), or due to an enclosure preventing user access to the laser beam during normal operation, such as in CD players or laser printers.

Class II

The blink reflex of the human eye will prevent eye damage, unless the person deliberately stares into the beam for an extended period. Output power may be up to 1 mW. This class includes only lasers that emit visible light. Most laser pointers are in this category.

Class IIa

A region in the low-power end of Class II where the laser requires in excess of 1,000 seconds of continuous viewing to produce a burn to the retina. Commercial laser scanners are in this subclass.

Class IIIa

Lasers in this class are mostly dangerous in combination with optical instruments which change the beam diameter or power density, though even without optical instrument enhancement direct contact with the eye for over two minutes may cause serious damage to the retina.

Class IIIb

Lasers in this class may cause damage if the beam enters the eye directly. This generally applies to lasers powered from 5–500 mW.

Class IV

Lasers in this class have output powers of more than 500 mW in the beam and may cause severe, permanent damage to eye or skin without being magnified by optics of eye or instrumentation.