IRC-Galleria

kaikki kusee;o

ollaan oltu yhes jo 2vrk, hän ei ole ottanut lääkkeitään

kummallisia datiksia:o

A laser is an electronic-optical device that emits coherent light radiation. The term "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. A typical laser emits light in a narrow, low-divergence beam, with a narrow wavelength spectrum ("monochromatic" light). In this respect, laser light is in sharp contrast with such light sources as the incandescent light bulb, which emits incoherent light (out of phase with itself) over a wide area and over a wide spectrum of wavelengths, and differs from LED light which is not coherent.

The first working laser was demonstrated on May 16, 1960 by Theodore Maiman at Hughes Research Laboratories. Since then, lasers have become a multi-billion dollar industry. The most widespread[citation needed] use of lasers is in optical storage devices such as compact disc and DVD players, in which the laser (a few millimeters in size) scans the surface of the disc. Other common applications of lasers are bar code readers, laser printers and laser pointers.

In industry, lasers are used for cutting steel and other metals and for inscribing patterns (such as the letters on computer keyboards). Lasers are also commonly used in various fields in science, especially spectroscopy, typically because of their well-defined wavelength or short pulse duration in the case of pulsed lasers. Lasers are used by the military for rangefinding, target identification and illumination for weapons delivery. Lasers have also recently begun to be used as weapons. Lasers used in medicine are used for internal surgery and cosmetic applications.

A laser consists of a gain medium inside a highly reflective optical cavity, as well as a means to supply energy to the gain medium. The gain medium is a material with properties that allow it to amplify light by stimulated emission. In its simplest form, a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium. Typically one of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror.

Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium, being amplified repeatedly. Part of the light that is between the mirrors (that is, within the cavity) passes through the partially transparent mirror and escapes as a beam of light.

The process of supplying the energy required for the amplification is called pumping. The energy is typically supplied as an electrical current or as light at a different wavelength. Such light may be provided by a flash lamp or perhaps another laser. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.

The word laser originated as an acronym for light amplification by stimulated emission of radiation. The word light in this phrase is used in the broader sense, referring to electromagnetic radiation of any frequency, not just that in the visible spectrum. Hence there are infrared lasers, ultraviolet lasers, X-ray lasers, etc. Because the microwave equivalent of the laser, the maser, was developed first, devices that emit microwave and radio frequencies are usually called masers. In early literature, particularly from researchers at Bell Telephone Laboratories, the laser was often called the optical maser. This usage has since become uncommon, and as of 1998 even Bell Labs uses the term laser.

The back-formed verb to lase means "to produce laser light" or "to apply laser light to". The word "laser" is sometimes used to describe other non-light technologies. For example, a source of atoms in a coherent state is called an "atom laser".

The gain medium of a laser is a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission. It can be of any state: gas, liquid, solid or plasma. The gain medium absorbs pump energy, which raises some electrons into higher-energy ("excited") quantum states. Particles can interact with light both by absorbing photons or by emitting photons. Emission can be spontaneous or stimulated. In the latter case, the photon is emitted in the same direction as the light that is passing by. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved and the amount of stimulated emission due to light that passes through is larger than the amount of absorption. Hence, the light is amplified. By itself, this makes an optical amplifier. When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser.

The light generated by stimulated emission is very similar to the input signal in terms of wavelength, phase, and polarization. This gives laser light its characteristic coherence, and allows it to maintain the uniform polarization and often monochromaticity established by the optical cavity design.

The optical cavity, a type of cavity resonator, contains a coherent beam of light between reflective surfaces so that the light passes through the gain medium more than once before it is emitted from the output aperture or lost to diffraction or absorption. As light circulates through the cavity, passing through the gain medium, if the gain (amplification) in the medium is stronger than the resonator losses, the power of the circulating light can rise exponentially. But each stimulated emission event returns a particle from its excited state to the ground state, reducing the capacity of the gain medium for further amplification. When this effect becomes strong, the gain is said to be saturated. The balance of pump power against gain saturation and cavity losses produces an equilibrium value of the laser power inside the cavity; this equilibrium determines the operating point of the laser. If the chosen pump power is too small, the gain is not sufficient to overcome the resonator losses, and the laser will emit only very small light powers. The minimum pump power needed to begin laser action is called the lasing threshold. The gain medium will amplify any photons passing through it, regardless of direction; but only the photons aligned with the cavity manage to pass more than once through the medium and so have significant amplification.

The beam in the cavity and the output beam of the laser, if they occur in free space rather than waveguides (as in an optical fiber laser), are, at best, low order Gaussian beams. However this is rarely the case with powerful lasers. If the beam is not a low-order Gaussian shape, the transverse modes of the beam can be described as a superposition of Hermite-Gaussian or Laguerre-Gaussian beams (for stable-cavity lasers). Unstable laser resonators on the other hand, have been shown to produce fractal shaped beams. The beam may be highly collimated, that is being parallel without diverging. However, a perfectly collimated beam cannot be created, due to diffraction. The beam remains collimated over a distance which varies with the square of the beam diameter, and eventually diverges at an angle which varies inversely with the beam diameter. Thus, a beam generated by a small laboratory laser such as a helium-neon laser spreads to about 1.6 kilometers (1 mile) diameter if shone from the Earth to the Moon. By comparison, the output of a typical semiconductor laser, due to its small diameter, diverges almost as soon as it leaves the aperture, at an angle of anything up to 50°. However, such a divergent beam can be transformed into a collimated beam by means of a lens. In contrast, the light from non-laser light sources cannot be collimated by optics as well.

Although the laser phenomenon was discovered with the help of quantum physics, it is not essentially more quantum mechanical than other light sources. The operation of a free electron laser can be explained without reference to quantum mechanics.

The output of a laser may be a continuous constant-amplitude output (known as CW or continuous wave); or pulsed, by using the techniques of Q-switching, modelocking, or gain-switching. In pulsed operation, much higher peak powers can be achieved.

Some types of lasers, such as dye lasers and vibronic solid-state lasers can produce light over a broad range of wavelengths; this property makes them suitable for generating extremely short pulses of light, on the order of a few femtoseconds (10-15 s).

In the continuous wave (CW) mode of operation, the output of a laser is relatively consistent with respect to time. The population inversion required for lasing is continually maintained by a steady pump source.

In the pulsed mode of operation, the output of a laser varies with respect to time, typically taking the form of alternating 'on' and 'off' periods. In many applications one aims to deposit as much energy as possible at a given place in as short time as possible. In laser ablation for example, a small volume of material at the surface of a work piece might evaporate if it gets the energy required to heat it up far enough in very short time. If, however, the same energy is spread over a longer time, the heat may have time to disperse into the bulk of the piece, and less material evaporates. There are a number of methods to achieve this.

Montako tuntia yleensä nukut yössä? - 1-3

NYKYHETKI
Avonaiset msn keskustelusi? 17

KULUNUT VUOSI
Oletko kokenut surua? - Aika massiivisesti=D

MILLOIN
Milloin viimeksi joku kielsi sinulta jotakin todella tärkeää? - Pari viikkoo sitte:D mut menin silti kotiin ;) oon raggari
Milloin viimeksi haukuit jonkun pystyyn? - Viikon aikana, Päästiin stevenssistä eroon<3

OLETKO

Oletko koskaan hävennyt ketään kaveriasi? Miksi? - Ei semmoset oo kavereita:D

MENE SAAPUNEISIIN TEKSTIVIESTEIHIN
Keneltä on viesti numero 2? - Miika;o
Entä numero 10? - Sanna-Mari
Mitä lukee viestissä numero 23? - Heh.. :-D kyllä vain. :-D kannattaa sitä kaikki hommata. :)
Mitä lukee viestissä numero 27? - Hah.. Ai, mie ku luulin et sie meikkaat joka päivä.. :-D
Keneltä on viesti numero 30? - Sanna-Mari;o pelottavaa, ei siltä yleensä mitään tule:o

Ei oo ikinä ollu porukoiden kaa onkelmia, juu poliisi ampu:D
PYSÄHDY TAI AMMUN SÄHKÖÄ
KÄSI POIS TASKUSTA
BOOM<3
oliha sitä pakko kokeilla, ei se satu. gogogo(oon kannustava)

Ne löys nopeesti, ois pitäny jäädä sinne mehtään kykkii mut ajattelin liikkuu lämpimän vuoksi;)

Nyt lihakset kipeenä(ne kaikki), tapahtui toissa yönä kolmen aikaan 5minuuttia siitä kun yritin soittaa Julialle:D