A report on Laser pointer

Red (635 nm), blueish violet (445 nm), and green (520 nm) laser pointers
Trails by a 15 mW green laser pointer in a time exposure of a living room at night
A 5 mW green laser pointer directed at a palm tree at night. Note that the beam itself is visible through Rayleigh scattering.
Laser level used in construction.

Small handheld device with a power source and a laser diode emitting a very narrow coherent low-powered laser beam of visible light, intended to be used to highlight something of interest by illuminating it with a small bright spot of colored light.

- Laser pointer
Red (635 nm), blueish violet (445 nm), and green (520 nm) laser pointers

11 related topics with Alpha

Overall

Neodymium ions in various types of ionic crystals, and also in glasses, act as a laser gain medium, typically emitting 1,064 nm light from a particular atomic transition in the neodymium ion, after being "pumped" into excitation from an external source. Selection of 946 nm transition light is possible, as well

Diode-pumped solid-state laser

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Solid-state laser made by pumping a solid gain medium, for example, a ruby or a neodymium-doped YAG crystal, with a laser diode.

Solid-state laser made by pumping a solid gain medium, for example, a ruby or a neodymium-doped YAG crystal, with a laser diode.

Neodymium ions in various types of ionic crystals, and also in glasses, act as a laser gain medium, typically emitting 1,064 nm light from a particular atomic transition in the neodymium ion, after being "pumped" into excitation from an external source. Selection of 946 nm transition light is possible, as well

DPSSLs have advantages in compactness and efficiency over other types, and high power DPSSLs have replaced ion lasers and flashlamp-pumped lasers in many scientific applications, and are now appearing commonly in green and other color laser pointers.

Energy level scheme of SHG process.

Second-harmonic generation

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Nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of the initial photons (equivalently, twice the frequency and half the wavelength), that conserves the coherence of the excitation.

Nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of the initial photons (equivalently, twice the frequency and half the wavelength), that conserves the coherence of the excitation.

Energy level scheme of SHG process.
Schematic view of the SHG conversion of an exciting wave in a non-linear medium with a non-zero second-order non-linear susceptibility.
An electron (purple) is being pushed side-to-side by a sinusoidally-oscillating force, i.e. the light's electric field. But because the electron is in an anharmonic potential energy environment (black curve), the electron motion is not sinusoidal. The three arrows show the Fourier series of the motion: The blue arrow corresponds to ordinary (linear) susceptibility, the green arrow corresponds to second-harmonic generation, and the red arrow corresponds to optical rectification.
Different types of second-harmonic generation phase-matching of a coherent light for strong conversion. The case of negative crystals.
Diagram of the second-harmonic generation process.
A depiction of the second-harmonic generation setup for measuring the orientation of phenol at the air-water interface.
Cartoon depicting ordered molecules at a small spherical surface. An ultrafast pump laser pumps light with frequency ω which generates light at 2ω from the locally non-centrosymmetric media.
SHG radiation pattern excited with a Gaussian beam, in a homogeneous medium (A), or at an interface between opposite polarities that is parallel to the propagation (B). Only the forward SHG is represented.
SHG radiation pattern in forward (F) and backward (B) from different dipoles arangment: (a) single dipoles, thus F = B ; (b) a small stack of dipoles, F > B ; (c) a large stack of dipoles, F >> B ; (d) the Gouy phase-shift cancels the SHGs, F&B weak
Intensity SHG, phase-matched or not. The medium width is supposed to be much higher than z, the Rayleigh range at 20µm, excitation wavelength of 0.8µm, and optical index of 2.2.

Nevertheless, some "green laser pointer" products have become available on the market which omit the expensive infrared filter, often without warning.

Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers

Laser

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Device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

Device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers
A laser beam used for welding
frameless
A helium–neon laser demonstration. The glow running through the center of the tube is an electric discharge. This glowing plasma is the gain medium for the laser. The laser produces a tiny, intense spot on the screen to the right. The center of the spot appears white because the image is overexposed there.
Spectrum of a helium–neon laser. The actual bandwidth is much narrower than shown; the spectrum is limited by the measuring apparatus.
Lidar measurements of lunar topography made by Clementine mission.
Laserlink point to point optical wireless network
Mercury Laser Altimeter (MLA) of the MESSENGER spacecraft
Aleksandr Prokhorov
Charles H. Townes
LASER notebook: First page of the notebook wherein Gordon Gould coined the acronym LASER, and described the elements required to construct one. Manuscript text: "Some rough calculations on the feasibility / of a LASER: Light Amplification by Stimulated / Emission of Radiation. /
Conceive a tube terminated by optically flat / [Sketch of a tube] / partially reflecting parallel mirrors..."
Graph showing the history of maximum laser pulse intensity throughout the past 40 years.
Wavelengths of commercially available lasers. Laser types with distinct laser lines are shown above the wavelength bar, while below are shown lasers that can emit in a wavelength range. The color codifies the type of laser material (see the figure description for more details).
A 50 W FASOR, based on a Nd:YAG laser, used at the Starfire Optical Range
A 5.6 mm 'closed can' commercial laser diode, such as those used in a CD or DVD player
Close-up of a table-top dye laser based on Rhodamine 6G
The free-electron laser FELIX at the FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein
Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other high energy density physics experiments.
The US–Israeli Tactical High Energy weapon has been used to shoot down rockets and artillery shells.
Laser application in astronomical adaptive optics imaging

Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers and lidar (light detection and ranging).

A packaged laser diode shown with a penny for scale

Laser diode

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Semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction.

Semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction.

A packaged laser diode shown with a penny for scale
The laser diode chip removed and placed on the eye of a needle for scale
A laser diode with the case cut away. The laser diode chip is the small black chip at the front; a photodiode at the back is used to control output power.
SEM (scanning electron microscope) image of a commercial laser diode with its case and window cut away. The anode connection on the right has been accidentally broken by the case cut process.
Semi-conductor lasers (660 nm, 635 nm, 532 nm, 520 nm, 445 nm, 405 nm)
Diagram of a simple laser diode, such as shown above; not to scale
A simple and low power metal enclosed laser diode
Nick Holonyak
Diagram of front view of a double heterostructure laser diode; not to scale
Diagram of front view of a simple quantum well laser diode; not to scale
Diagram of front view of a separate confinement heterostructure quantum well laser diode; not to scale
Diagram of a simple VCSEL structure; not to scale
Laser diodes can be arrayed to produce very high power outputs, continuous wave or pulsed. Such arrays may be used to efficiently pump solid-state lasers for high average power drilling, burning or for inertial confinement fusion

Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination.

Structure of KTP viewed down b axis. Color code: red = O, purple = P, bright blue = K, dark blue = Ti).

Potassium titanyl phosphate

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Inorganic compound with the formula KTiOPO4.

Inorganic compound with the formula KTiOPO4.

Structure of KTP viewed down b axis. Color code: red = O, purple = P, bright blue = K, dark blue = Ti).

KTP crystals coupled with Nd:YAG or Nd:YVO4 crystals are commonly found in green laser pointers.

Carl Auer von Welsbach (1858–1929), the discoverer of neodymium in 1885.

Neodymium

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Chemical element with the symbol Nd and atomic number 60.

Chemical element with the symbol Nd and atomic number 60.

Carl Auer von Welsbach (1858–1929), the discoverer of neodymium in 1885.
Bastnäsite
Neodymium is a fairly common element in the Earth's crust for being a rare-earth metal. Most rare-earth metals are less abundant.
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Neodymium magnet on a mu-metal bracket from a hard drive
A neodymium glass light bulb, with the base and inner coating removed, under two different types of light: fluorescent on the left, and incandescent on the right.
Didymium glasses
Nd:YAG laser rod
Neodymium doped glass slabs used in extremely powerful lasers for inertial confinement fusion.
Neodymium ions in various types of ionic crystals, and also in glasses, act as a laser gain medium, typically emitting 1064 nm light from a particular atomic transition in the neodymium ion, after being "pumped" into excitation from an external source
Neodymium compounds in fluorescent tube light—from left to right, the sulfate, nitrate, and chloride
Neodymium compounds in compact fluorescent lamp light
Neodymium compounds in normal daylight

Neodymium-doped crystals (typically Nd:YVO4) generate high-powered infrared laser beams which are converted to green laser light in commercial DPSS hand-held lasers and laser pointers.

Mobile robot guidance by laser beam (sketch)

Laser guidance

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Laser guidance directs a robotics system to a target position by means of a laser beam.

Laser guidance directs a robotics system to a target position by means of a laser beam.

Mobile robot guidance by laser beam (sketch)

Examples of proof-of-concept experiments of directing a robot by a laser pointer are shown on video.

A laser warning symbol

Laser safety

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Safe design, use and implementation of lasers to minimize the risk of laser accidents, especially those involving eye injuries.

Safe design, use and implementation of lasers to minimize the risk of laser accidents, especially those involving eye injuries.

A laser warning symbol
Diagram of a human eye
A typical US (ANSI) laser warning label
Maximum permissible exposure (MPE) at the cornea for a collimated laser beam according to IEC 60825, as energy density versus exposure time for various wavelengths
MPE as power density versus exposure time for various wavelengths
MPE as energy density versus wavelength for various exposure times (pulse durations)
The maximal allowed cw-powers for the laser classes 1, 2, 3R and 3B according to the standard EN 60825-1:2007. Note that these values hold only for static, point-like laser sources (i.e. collimated or weakly divergent laser beams).
Warning label for class 2 and higher
Green laser – class IIIb compared to class IIIa
Laser goggles
Laser pointers

Some laser pointers and measuring instruments are class 2.

Flash blindness

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Flash blindness is an either temporary or permanent visual impairment during and following exposure of a varying length of time to a light flash of extremely high intensity, such as a nuclear explosion, flash photograph, lightning strike, or extremely bright light, i.e. a searchlight or laser pointer or landing lights or ultraviolet light.

Police used tear gas to disperse protesters gathering outside the Legislative Council Complex on 12 June 2019.

2019–2020 Hong Kong protests

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The Anti-Extradition Law Amendment Bill Movement, also known as the 2019 Hong Kong protests, or the 2019–2020 Hong Kong protests, were a series of demonstrations from 15 March 2019 in response to the introduction by the Hong Kong government of the Fugitive Offenders amendment bill on extradition.

The Anti-Extradition Law Amendment Bill Movement, also known as the 2019 Hong Kong protests, or the 2019–2020 Hong Kong protests, were a series of demonstrations from 15 March 2019 in response to the introduction by the Hong Kong government of the Fugitive Offenders amendment bill on extradition.

Police used tear gas to disperse protesters gathering outside the Legislative Council Complex on 12 June 2019.
Marco Leung Ling-kit on scaffolding at Pacific Place before he fell to his death on 15 June
Protesters briefly occupied the Legislative Council Complex on 1 July 2019.
Protesters pointing their laser pointers at a newspaper outside the Space Museum, mocking an earlier police demonstration that aimed to illustrate the danger of laser pointers, which was seized from an arrested student-union president
Tsang Chi-kin, 18, was shot in the chest by police in 2019
The police confronted the protesters at the entrance of the Chinese University of Hong Kong on 12 November 2019.
Protesters in Yau Ma Tei on 18 November 2019 as they attempted to breach the police's cordon line to break through to protesters trapped inside Hong Kong Polytechnic University
Protesters flood the streets during the New Year's march
The national security law banned anyone from shouting or displaying the slogan "Liberate Hong Kong, the revolution of our times", which has achieved mainstream adoption since July 2019.
Civic Party promoting the primaries as the democrats aspired to secure a majority in LegCo. Four candidates from the party were disqualified by the government.
Former lawmaker Nathan Law met with US Secretary of State Mike Pompeo in July 2020, discussing matters concerning the national security law, the pro-democratic primaries, and the LegCo election.
White-clad men assaulted commuters and protesters with sticks inside Yuen Long station on 21 July 2019.
A subway near Tai Po Market station, dubbed the "Lennon Tunnel"
Black Bauhinia Flag, a variation of the flag of Hong Kong
Pepe the Frog became a symbol of resistance during the protests. "Give me Liberty or Give me Death!" alludes to Patrick Henry's speech in support of the American Revolution.
A Winnie the Pooh toy used to symbolise Xi Jinping with the Chinazi flag stuck on it and a swastika shaped Chinese Flag attached on its chest, used in the 1 December 2019 protests
Protesters adopted the black bloc method and wore helmets and respirators to protect themselves. Yellow hard hats became a symbol for the protest movement
A "smart" lamppost was destroyed by protesters on 24 August 2019, due to understanding that it could be used for surveillance
A water cannon truck firing blue-dyed liquid at protesters
A police officer firing tear gas canisters on 31 August 2019
A passerby was attacked by riot police in Tai Wai on 3 October 2019
Veby Mega Indah, an Indonesian journalist whose right eye was ruptured by a police baton round
Stand News journalist Gwyneth Ho was attacked by a stick-wielding man during the Yuen Long attack on 21 July 2019.
Police near Lan Kwai Fong, Central on 31 October 2019. Police were accused of obstructing reporters from taking photographs by shining flashlights at them.
Protest at the Hong Kong International Airport on 26 July 2019
District councillors collaborated with shops supporting the Yellow Economic Circle to organise a Lunar New Year Fair in Sai Ying Pun on 18 January 2020.
Elderly marching on 17 July 2019 to support young people's anti-extradition bill protests
Chief Executive Carrie Lam at the press conference with Secretary for Justice Teresa Cheng and Secretary for Security John Lee one day after the massive protest on 9 June 2019.
Activists including Joshua Wong and Nathan Law met House Democratic leader Nancy Pelosi and Representative Chris Smith at the US Congress.

Furthermore, protesters used laser pointers to distract police officers and interfere with the operation of their cameras.