Laser

U Prahy spustili supersilný laser. Má výkon milion miliard wattů a stál přes miliardu

---

An universal model valid for all laser types does not exist. Within each sub-level system, the fast transitions ensure that thermal equilibrium is reached quickly, leading to the Maxwell—Boltzmann statistics of excitations among sub-levels in each system fig. The upper level is assumed to be metastable.

Also, gain and refractive index are assumed independent of a particular way of excitation. In the case of amplification of optical signals, the lasing frequency is called signal frequency. However, the same term is used even in the laser oscillators , when amplified radiation is used to transfer energy rather than information.

The model below seems to work well for most optically-pumped solid-state lasers. In many cases the gain medium works in a continuous-wave or quasi-continuous regime, causing the time derivatives of populations to be negligible.

Nd:YAG laser

The absorption at strong signal: The gain at strong pump: They produce a broad spectrum of light, causing most of the energy to be wasted as heat in the gain medium. Flashlamps also tend to have a short lifetime. Higher average powers or repetition rates require water cooling.

The water usually has to wash across not only the arc length of the lamp, but across the electrode portion of the glass as well. Water-cooled flashlamps are usually manufactured with the glass shrunken around the electrode to allow direct cooling of the tungsten. If the electrode is allowed to heat much more than the glass thermal expansion can crack the seal. Lamp lifetime depends primarily on the energy regime used for the particular lamp. Low energies give rise to sputter , which can remove material from the cathode and redeposit it on the glass, creating a darkened, mirrored appearance.

The life expectancy at low energies can be quite unpredictable. High energies cause wall ablation , which not only gives the glass a cloudy appearance, but also weakens it structurally and releases oxygen , affecting pressure, but at these energy levels the life expectancy can be calculated with a fair amount of accuracy. Pulse duration can also affect lifetime.

Very long pulses can strip large amounts of material from the cathode, depositing it on the walls. With very short pulse durations, care must be taken to ensure that the arc is centered in the lamp, far away from the glass, preventing serious wall ablation. Dye lasers sometimes use "axial pumping," which consists of a hollow, annular shaped flashlamp, with the outer envelope mirrored to reflect suitable light back to the center.

The dye cell is placed in the middle, providing a more even distribution of pumping light, and more efficient transfer of energy. The hollow flashlamp also has lower inductance than a normal flashlamp, which provides a shorter flash discharge. Rarely, a "coaxial" design is used for dye lasers, which consists of a normal flashlamp surrounded by an annular shaped dye cell.

This provides better transfer efficiency, eliminating the need for a reflector, but diffraction losses cause a lower gain. The output spectrum of a flashlamp is primarily a product of its current density.

The Pros and Cons of CubeSats

Low current densities result from the use of very high voltage and low current. Higher current densities broaden the spectral lines to the point where they begin to blend together, and continuum emission is produced. Longer wavelengths reach saturation levels at lower current densities than shorter wavelengths, so as current is increased the output center will shift toward the visual spectrum, which is better for pumping visible light lasers, such as ruby.

Xenon is used extensively because of its good efficiency, [11] although krypton is often used for pumping neodymium doped laser rods.

This is because the spectral lines in the near-IR range better match the absorption lines of neodymium, giving krypton better transfer efficiency even though its overall power output is lower. YAG, which has a narrow absorption profile. Pumped with krypton, these lasers can achieve up to twice the output power obtainable from xenon. YAG with krypton, but since all of xenon's spectral lines miss the absorption bands of Nd: YAG, when pumping with xenon the continuum emission is used.

Arc lamps are used for pumping rods that can support continuous operation, and can be made any size and power. Typical arc lamps operate at a voltage high enough to maintain the certain current level for which the lamp was designed to operate. This is often in the range of 10 to 50 amps. Due to their very high pressures, arc lamps require specially designed circuitry for start up, or "striking" the arc. Striking usually occurs in three phases. In the triggering phase, an extremely high voltage pulse from the "series triggering" transformer creates a spark streamer between the electrodes, but the impedance is too high for the main voltage to take over.

A "boost voltage" phase is then initiated, where a voltage that is higher than the voltage drop between the electrodes is driven through the lamp, until the gas is heated to a plasma state. When impedance becomes low enough, the "current control" phase takes over, where as the main voltage begins to drive the current to a stable level. Arc lamp pumping takes place in a cavity similar to a flashlamp pumped laser, with a rod and one or more lamps in a reflector cavity.

The exact shape of the cavity is often dependent on how many lamps are used. The main difference is in the cooling. Arc lamps need to be cooled with water, ensuring that the water washes beyond the glass, and across the electrode connectors as well. This requires the use of deionized water with a resistivity of at least kilohms, to keep from shorting out the circuit and corroding the electrodes through electrolysis. Water is typically channeled through a flow tube at a rate of 4 to 10 liters per minute. Arc lamps come in nearly all of the noble gas types, including xenon , krypton , argon , neon , and helium , which all emit spectral lines that are very specific to the gas.

The output spectrum of an arc lamp is mostly dependent on the gas type, being narrow band spectral lines very similar to a flashlamp operated at low current densities.

Some laser gain media offer laser transitions with nearly ideal characteristics. For example, the neodymium ions in Nd: Efficient pumping is possible e. There are also media with quasi-three-level laser transitions , where the last condition is not well fulfilled, because the lower level belongs to the ground state manifold.

laser | Definition, Acronym, Principle, Applications, & Types | www.farmersmarketmusic.com

Examples are the nm and the nm transitions in Yb: The resulting reabsorption on the laser transition tends to increase the threshold pump power , but on the other hand such transitions can have a rather low quantum defect , and thus allow fairly efficient laser operation provided that the laser design is optimized accordingly. If you like this article, share it with your friends and colleagues, e. Sorry, we don't have an article for that keyword!

A New Era for CubeSats

• The Practice of Piety: Puritan Devotional Disciplines in Seventeenth-Century New England (Published for the Omohundro Institute of Early American History and Culture, Williamsburg, Virginia)
• The One Year Marriage: A Formula for Enduring Love
• Cogs and Corsets: A Steampunk Collection volume 1
• I Lost Sight of the World
• A narrative of the life of David Crockett .. (1834)