Laser safety

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Construction of a Laser
• Pump Source
The pump source is the part that provides energy to the laser system. Examples of pump sources include electrical discharges, flash lamps, arc lamps, light from another laser, chemical reactions and even explosive devices. The type of pump source used principally depends on the gain medium, and this also determines how the energy is transmitted to the medium.
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Construction of a Laser
• Optical Resonator
Optical resonator, its simplest form is two parallel mirrors placed around the gain medium which provide feedback of the light.
* a beam generated by a small laboratory laser such as a He-Ne laser spreads to about 1.6 kilometers diameter if shine from the earth to the moon. By comparison, the output of a typical diode laser, due to its small diameter, diverges almost as soon as it leaves the aperture, at an angle of anything up to 50°.
Quantifying Light
• Example of Quantifying Light
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Quantifying Light
• Power and Energy
Quantifying Light
• Pulsed Laser
Q = ∫ P(t )dt
t1
t2
• Pulse duration:
defined as the FWHM (full-width half-maximum value) • Period of pulse train: time between maxima of two consecutive pulses
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Quantifying Ligபைடு நூலகம்t
• Irradiance and Radiant Exposure
Construction of a Laser
• Gain Medium
The gain medium is the major determining factor of the wavelength of operation, and other properties of the laser. There are hundreds of different gain media in which laser operation has been achieved. The gain medium is excited by the pump source to produce a population inversion, and it is in the gain medium that spontaneous and stimulated emission of photons takes place, leading to the phenomenon of optical gain, or amplification.
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Collimated beam
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Properties of Laser Radiation
• Monochromaticity
Properties of Laser Radiation
• Coherence
Laser light is usually spatially coherence, which means that the light either is emitted in a narrow, low-divergence beam.
In more complex lasers, configurations with four or more mirrors forming the cavity are used.
Diverging beam
An example of an optical collimating lens.
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Typically one mirrors will be a high reflector, and the other will be a partial reflector.
Properties of Laser Radiation
• Collimated Beam
Laser light from gas or crystal lasers is naturally collimated because it is formed in an optical cavity between two mirrors. The divergence of high-quality laser beams is commonly less than 1mrad, and can be much less for large-diameter beams. It should be noted that diode lasers do not naturally emit collimated light, and therefore collimation into a beam requires a collimating lens.
History of Laser
• Definition
LASER is an acronym for Light Amplification by the Stimulated Emission of Radiation
• In 1917, Albert Einstein first theorized about the process which makes lasers possible
• In 1961, the first ruby laser of China was produced in Changchun Institute of Optic, fine
mechanics, Chinese academy of sciences.
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What is Laser
Light from the medium, produced by spontaneous emission, is reflected by the mirrors back into the medium, where it may be amplified by stimulated emission. The light may reflect from the mirrors and thus pass through the gain medium many hundreds of times before exiting the cavity.
A He-Ne laser uses an electrical discharge in the helium-neon gas mixture, A Nd: YAG laser uses either light focused from a xenon flash lamp or diode lasers.
Recording
Laser Hologram
Reconstruction
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Quantifying Light
• Photometric Units & Radiometric Units
Used for illumination purpose, light quantities expressed in photometric units: (Lumen, Lux, Candela) Other than illumination purpose and the ability of light to cause damage, in light safety assessment, radiometric units used: power and energy (1W=1J/s) Usually, express the emission of CW or steady state laser in power (P), but to measure the output of pulse laser in energy (Q) of each pulse.
• What is Light ?
CIE 1931 Chromaticity Diagram
What is Laser
• Common Light Source
Spontaneous emission
Electromagnetic Radiation Spectrum
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called “Stimulated Emission.”
• In 1954, Charles Townes and Arthur Schawlow invented the Maser (microwave
amplification by stimulated emission of radiation), the technology is very close to Laser. In 1958, Charles Townes and Arthur Schawlow theorized and published papers about a visible laser, an invention that would use infrared and/or visible spectrum light.
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What is Laser
• Laser
Stimulated emission
Construction of a Laser
• A Laser is Constructed from Three Principal Parts
1) An energy source (usually referred to as the pump or pump source) 2) A gain medium or laser medium 3) Two or more mirrors that form an optical resonator
Laser Safety
• In 1960, Theodore Maiman invented the ruby laser considered to be the first successful
optical or light laser. *Many historians claim that Theodore Maiman invented the first optical laser, however, there is some controversy that Gordon Gould was the first.