Amplification, in laser

Note that parameters ft and 5 depend on signal amplifications in the utilized detectors and on the elements in the optical path (optical filter, spectral detection bands) only, while a and y are additionally influenced by relative excitation intensity. This is usually a fixed constant in wide-field microscopy but in confocal imaging laser line intensities are adjusted independently. Furthermore, note that the a factor equals 5 multiplied by y (see Appendix for further detail). 

Now today, we have found about a hundred different masers in space and some lasers. The difference between a maser and a laser is of course only in the wavelength. But there are some astronomical systems where infrared is getting amplified. Now as has been pointed out, amplification in interstellar space doesn t involve resonances, but it does involve stimulated emission. You know, somebody could have seen these interstellar masers in the radio regions of the spectrum many years ago. Anybody who used the radio technology of 1936, and looked up into the sky, could have detected this water frequency. They didn t bother to look, but it was there all the time. So now we know, lasers have been there for billions of years. Masers have been there billions of years. So that s another way we might have discovered them, but we didn t. Now I emphasize this to indicate that we need to search, we mustn t be too confined by what we think is going to work, we ve got to explore. 

Laser oscillation will start when V (t) has increased to such a value that the overall amplification in one round trip of a photon through the laser resonator is greater than unity, resulting in the oscillation condition... 

Gragson DE, Alavi DS, Richmond GL. Tunable picosecond infrared laser system based on parametric amplification in KTP with a Ti sapphire amplifier. Opt Lett 1995 20 1991-1993. 

The 4Ii3/2 - 4Iis/2 infrared emission band of Er3+ ions in fluorozirconate glass is displayed in Fig. 11. The band maximum is located at 1.53 /an and the width at half-maximum is as broad as 60 nm, which favors the use of this transition for optical amplification in the third telecommunication window. In bulk geometry, 1.6 jtm CW-laser action is reported for a Cr, Yb, Er-codoped fluoroaluminate glass slab pumped by a krypton laser [114],... 

The 800 nm transition from 3H4 to 3H6 has been extensively studied because of its suitability for optical amplification in the first telecommunication window. With a branching ratio of 90%, this transition is not perturbed by amplified spontaneous emission of competing transitions. The 1.47 jum emission from 3H4 to 3F4 is also of special interest for optical amplification between the second and third telecommunication window. Both transitions arise from the 3H4 level, which can be excited directly at 800 nm with a laser diode. This level can also be pumped by 2-step up-conversion, either from a mini-YAG Nd at 1.06 m or from a laser diode at 975 nm, in (Yb, Tm) codoped glasses. Details on these applications are given in Sec. 8.5.2. 

As we saw in Section 5.5, the rate of absorption between two molecular energy levels E] and E2 is exactly equal to the rate of stimulated emission, for a given density of resonant photons, with co = E2 — E )/h. Whether there will be net absorption or emission depends on the relative populations, N and N2, of the two levels. At thermal equilibrium, when the populations follow a Boltzmann distribution, with the lower level E more populated than the upper level E2, a net absorption of radiation of frequency w can occur. If the two populations are equal, there will be neither net absortion or emission since the rates of upward and downward transitions will exactly balance. Only if we can somehow contrive to achieve a population inversion, with N2> N, can we achieve net emission, which amounts to amplification of the radiation (the A in LASER). Thus, to construct a laser, the first requirement is to produce a population inversion. Laser action can then be triggered by a few molecules undergoing spontaneous emission. 

Some of the relevant applications of nonlinear optics are currently used in laser technology and fiber communications, such as optical frequency conversion, optical parametric oscillation and amplification, the linear electrooptic effect (Pockels... 

The word laser is an acronym for light amplification by stimulated emission of radiation. Lasers have a number of applications besides light shows. Find out how lasers are produced, what substances are used in lasers, and the ways laser light is used. Write a paper describing your findings. 

Near-IR solid-state lasers (e.g., Ti sapphire) with chirped pulse amplification produce laser light with high brightness and very short pulses around 800 nm [ 116]. 150 fs laser pulse experiments on PI, polycarbonates (PC), PET, and PMMA have shown an increase in the single pulse ablation threshold from 1 J/cm for PI to 2.6 J/cm for PMMA. This corresponds well with the optical bandgaps of these polymers and indicates a multiphoton process. Incubation effects were observed for all polymers, but are more pronounced for PMMA, PC, and PET than for PI and PTFE, which are more stable [117-120]. Clear signs of molt redeposition of material can be observed for all polymers, except PI, which is not surprising, as it decomposes and does not melt. 

Instead of measuring the attenuation of a beam, one may also count the ions produced with very high efficiency by the use of channelplates or a hot-wire detector [387], an approach which has mainly been applied in laser spectroscopy, where high sensitivity can be achieved by space charge amplification. The principle of the thermionic diode is that the atomic vapour under study is formed within the detector, and a current limited by the space charge is obtained by appropriately biasing a diode, consisting of an external anode (often the outer wall of the vacuum system, formed by a metal tube) and a heated cathode made of a suitable material to emit many electrons (thoriated W is suitable in many cases). A sketch of... 

Fig. 2. Lay-out of the Lund High-Power Laser Facility terawatt system, which operates with chirped-pulse amplification in titanium-doped sapphire (Adopted from Ref. [3]).

An alternative approach to pooling, in the analysis of small samples, is RNA amplification. In particular, this approach has been successfully used to derive enough RNA from sources such as laser capture microdissection... 

With F2 excimer laser lithography at 157 nm, even polymers based on aerylates and norbonenes are too opaque to be of any useful value in resist appheations. Therefore, fluorocarbons and silanol polymers are the two main classes of polymers that have reasonable transparency at this wavelength. Again, like their 193-nm and 248-nm counterparts, the 157-nm resists employ chemical amplification in their imaging mechanism, for quite similar reasons. 

E. Sorokin, Solid-state materials for few-cycle pulse generation and amplification, in Few Cycle Laser Pulses Generation and Its Applications, ed. by F.X. Kartner. Topics Appl. Phys., vol. 95 (Springer, Berlin, 2004), pp. 3-72... 

To achieve a sustained oscillation in a laser, amplification in the gain medium must at least balance out with the optical loss during each round-trip of the cavity. Therefore, when the pump rate increases beyond a threshold value, an intense coherent laser beam is generated whose power rises linearly with the excess pump rate. At low pumping rates, the excitations in the gain medium are radiated in all directions as spontaneous emission. 

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