Laser pointer
The laser pointer is a light pointer especially for presentations with projection . Laser pointers are made in handy sizes, also in the form of key fobs, ballpoint pens or in combination with remote controls ( presenters ). While the first laser pointers only emitted red light (first He-Ne laser , then red laser diode ), blue, yellow and orange came onto the market after green.
With the increase in performance and efficiency of semiconductor diode lasers, inexpensive battery-operated lasers in the format of laser pointers became available, the light output of which is sometimes above the limit values of laser class 2 or 2M , which are still considered harmless to the eye when exposed to short-term radiation. These beam sources are also sold as laser pointers, but their use is associated with high risks of injuring people and being prosecuted for damage caused.
history
Before laser diodes were available at all and then also cheaply, there were so-called light pointers (example :), which consisted of a modified flashlight . Instead of a concave mirror, the lamp was equipped with a lens optic so that an arrow symbol (flat or as an outline) could be projected with a simple slide projector . The advantage of this arrangement was the arrow symbol, with which you could point something more meaningful than with the simple point of a laser pointer. There were also E10 special light bulbs in which the filament itself was designed in the shape of an arrow. The disadvantage was the mostly very low-light design and the need to constantly readjust the lens optics to adapt to the distance from the projection surface. These light pointers were offered by slide projector companies.
The first lasers used as pointers, miniaturized helium-neon lasers. But it was only with the availability of inexpensive and efficient laser diodes that the laser pointer achieved its breakthrough as a mass product.
Layout and function
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The following components are housed in the handy housing:
- Laser diode (also called semiconductor laser )
- Collimator - lens
- Batteries
- Electronic circuit for controlling the laser diode, mostly consisting of just a resistor
- Button
Since no high demands are made on the beam quality and other properties of laser pointers, mainly laser diodes are used here, which were classified as rejects during manufacture for industrial purposes.
A frequency-doubled DPSS laser (532 nm) is usually used for the green models . Since 2012, direct green laser diodes based on the semiconductor indium gallium nitride (InGaN) have also been available. The orange models use a mixture of two laser sources. Blue models use laser diodes or DPSS.
properties
power
The emitted light output is mostly below 3 mW; the laser thus corresponds to classes 1 to 3R. The spread of the power values is often very high with laser pointers - even with identical models - which means that laser pointers with output powers of 10 mW also occur (corresponds to class 3B, although these laser pointers are often not labeled accordingly).
According to the currently applicable standard EN 60825-1, lasers that emit in the visible wavelength range (400–700 nm) are classified as laser class 2 with an output power of up to 1 mW and as class 3R lasers with a power of <5 mW. Lasers with a power> 5 mW fall into class 3B and require additional safety devices and precautions such as wearing appropriate laser protection goggles . Chinese manufacturers in particular often sell lasers with a power of several watts in some cases; these lasers pose a considerable risk.
Lasers up to class 2 are considered to be conditionally harmless (safe for the eyes), as the eyelid closure reflex means that the exposure time is not sufficient to cause retinal damage. However, if the eyelid closing reflex is suppressed (e.g. manually), irradiation of the retina with class 2 lasers can also lead to damage. A scientific study showed that the blink reflex (this occurs within 0.25 s; longer exposure to radiation damages the eye) was only present in <20% of the test persons. According to the study, the presence of the blink reflex to protect the eyes cannot be assumed as a rule.
Divergence and color
The commercial divergence is approx. 1 mrad, i.e. H. the beam thickness increases by 1 mm / m.
In most cases, inexpensive red laser diodes with a wavelength of 635–750 nm are used. Green (490–575 nm) and significantly more expensive orange to yellow (575–635 nm) and blue (405–490 nm) laser pointers are also available. The human eye is about 10 times more sensitive to green light than to all other colors. If you compare green laser pointers with an equally powerful red laser, you will perceive the green laser as approx. 10 times brighter.
Side effects
In addition to creating a light spot on a projection screen, laser pointers can be used to observe some typical laser phenomena and to carry out experiments.
scattering
The shorter the wavelength, the more light is scattered in the air. This happens due to Rayleigh scattering , which increases sharply with decreasing wavelength. The eye is also particularly sensitive to green. Therefore, green and blue laser pointers can be used particularly well to observe the beam path.
Speckle pattern
If you look at the point of light from a laser pointer, you can see an optical effect called " speckles " or "granulation". The point of light does not appear uniformly bright, but granular, as if "flickering". You can see this effect particularly well if you expand the light with a lens and direct it onto a matt surface. This granulation is caused by interference in the eye, caused by the reflection of the coherent laser light on the not ideally smooth surface of the irradiated body. This partially overlaps the wavelengths of the laser, and places of constructive and destructive interference arise on the retina , which appear as light and dark spots.
Diffraction, interference, refraction
Optical experiments on diffraction and interference (e.g. irradiation of a tea strainer or a CD) as well as refraction and reflection can be carried out particularly well with laser pointers because the light is monochromatic and focused.
fluorescence
Violet, blue and, to a certain extent, also green laser pointers cause fluorescence in certain substances . These include B. fluorescent colors and remains of glow sticks . A common diode laser wavelength, also available as a pointer, is 405 nm, i.e. at the limit of visible light. These pointers are particularly suitable for fluorescence experiments, but are also particularly dangerous because the eye's sensitivity to light is very low at this wavelength.
Abuse of laser pointers
The misappropriation of laser pointers and mobile laser beam sources for deliberate glare is a danger. Class 2 lasers can in individual cases damage the retina temporarily or permanently and impair vision. Laser beams from devices with higher powers (Class 3R, 3B and 4) are declared as dangerous to the eye; operational use of these lasers is only permitted after the laser safety devices have been checked and the personnel have been instructed by a laser safety officer and the appropriate protective measures have been observed.
In the event of deliberate glare, this will result in criminal penalties. However, users are also liable for the dangers caused by the inability to act due to glare, for example in the case of drivers, train drivers or pilots. Football players and other athletes, referees and visitors to football matches have also been blinded at sporting events and other public events. In Germany, laser attacks on pilots can be seen as a dangerous interference in air traffic , the penalty ranges from probation and fines to imprisonment of ten years. Attempted murder can also be considered.
During the anti-Chinese protests in Hong Kong, protesters used powerful laser pointers to blind the police. Journalists' cameras were also damaged by laser pointers.
Legal position
Australia
Australia introduced some restrictive measures against high power laser pointers in 2008. Since July 2008 there has been an import ban for lasers> 1 mW. In parts of the country, such lasers and laser pointers fall under the Weapons Act.
Netherlands
The sale of laser pointers up to a maximum of 1 mW is permitted in the Netherlands.
Austria
In Austria, all laser pointers that are placed on the market must correspond to laser classes 1 or 2.
Sweden
In Sweden you need a permit to own a laser pointer over 1 mW.
Switzerland
In Switzerland, it has been forbidden since June 2019 to trade, own and import class 1M, 2, 2M, 3R, 3B and 4 laser pointers. In addition, the use of laser pointers outdoors was completely banned.
United Kingdom
The UK bans the sale of laser pointers with powers above 1 mW. The public safety guidelines prohibit the use of lasers above class 2 in public, where the laser light could endanger people.
United States
In the USA, the sale of beam sources under the designation laser pointers is only permitted for lasers below 5 mW (class 3R). In some states, in particular, dazzling police officers is a criminal offense. In 2014, 3894 laser attacks on aircraft were reported nationwide.
Web links
- Radiation Protection Commission (2010): Glare attacks from lasers: Recommendation of the Radiation Protection Commission
- The history of the laser pointer
Individual evidence
- ↑ A "light pointer" from Rhaco from the 50s. In: eichwaelder.de. November 27, 2008, accessed December 2, 2019 .
- ↑ Picture of a HeNe laser pointer
- ↑ LASER Diode-NICHIA CORPORATION
- ↑ Green Laser, Visible Laser - OSRAM Opto Semiconductors
- ↑ Laser pointers are long-running at customs in Frankfurt. In: extratipp.com. January 23, 2016, accessed December 2, 2019 .
- ↑ Laser pointer from China - about customs, colors, mW and bursting balloons ... In: china-gadgets.de. March 16, 2012, accessed December 2, 2019 .
- ↑ Thomas Müller: Great danger to children's eyes. In: aerztezeitung.de. September 9, 2016, accessed December 2, 2019 .
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↑ Reidenbach, H.-D .; Dollinger, K .; Hofmann, J .: Review of the laser classification taking into account the blink reflex . In: Series of publications by the Federal Institute for Occupational Safety and Health . Fb 985. Wirtschaftsverlag NW, Bremerhaven 2003, ISBN 978-3-89701-968-3 . Summary of human reactions to averting visible laser radiation (PDF; 120 kB).
- ↑ Eye injury from laser pointer. In: kaernten.orf.at. December 2, 2014, accessed December 2, 2019 .
- ↑ sueddeutsche.de January 26, 2011
- ^ More and more attacks with laser pointers Weser-Kurier, April 22, 2011
- ↑ 'No tears, no blood': Hongkongers stage huge laser show to protest against arrests. In: theguardian.com. August 8, 2019, accessed on August 27, 2019 .
- ^ Adam Jacobson: Hong Kong protesters use laser pointers to deter police, scramble facial recognition. In: cbc.ca. August 11, 2019, accessed on August 27, 2019 .
- ↑ Michael Zhang: Hong Kong Protester Lasers Are Frying Photographers' Cameras. In: petapixel.com. August 26, 2019, accessed on August 27, 2019 .
- ↑ Tecchannel: Laser pointers are now subject to the weapons law in Australia
- ^ RIS - LaserpointerV - Consolidated Federal Law, version of April 18, 2019. Retrieved April 18, 2019 .
- ↑ Switzerland forbids dangerous laser pointers. In: bag.admin.ch . June 3, 2019, accessed June 3, 2019 .
- ↑ Cyrus Farivar: “I'm so sorry. I'm stupid, ”says man who allegedly fired laser at police. In: arstechnica.com. February 21, 2015, accessed December 2, 2019 .
