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Semiconductor LASER 1) Law of Lambert:
it characterizes the variation of the intensity of a monochromatic optical bundle that propaga to the inside of a semiconductor, in it is the gain coefficient.
2) Coefficient of gain for a semiconductor bulk:
it becomes various from 0 for energies of the advanced photon to the energy gap and has a course to parabola invert whose maximum is moved towards greater energies to increasing of loads iniettata.
3) Reversal of population: It is had in the case in which the present electron density between the minimum of the conduction band and nearly the level of Firm of the same one he is greater of the present electron density between nearly the level of Firm of the valence band and the maximum of the valence band.
4) the maximum Gain:
it is therefore null for density of inferior bearers to the transparency density nt while beyond it has a linear course with equal slope to the gain differentiates them to.
5) Density of threshold current:
it is obtained imposing the condition stazionaria in the equation moreover since n it diminishes to diminishing of the temperature, consequently diminishes the density of threshold current.
6) ring Gain of the resonant cavity:
where R1 and R2 are the coefficients of reflection of the present mirrors in the cavity, L its length and g the coefficient of loss of the same one.
7) Gain of threshold: So that the oscillation autosostenga is necessary that the ring gain is unitary, imposing this condition is obtained in short, therefore the gain of the cavity must compensate the losses of same and the cancellation transmitted through the mirrors.
8) Ways you concur yourself in the resonant cavity: The ways you concur yourself in the cavity are only those for which the L length of the cavity is an entire multiple of average wavelengths, that is for which it is had .
9) Time of photonic life of the cavity:
it is in part which had to the losses of the cavity and in part to the transmission through the mirrors.
10) Coefficient of confinamento and relation with the threshold gain: Draft of the fraction of the electromagnetic way (…than extends in a wide region t) present to the inside of the wide active region d to the inside of which there is the contemporary presence of electrons and gaps.
the expression of the gain threshold would have to consider that all the electromagnetic way does not reside in the active region, that is would have therefore to be modified .
11) Installments equations:
12) electron and photon Concentration in function of the current density: To growing of the current density it increases to the concentration of bearers sin when it does not catch up the threshold value nth , to this point it remains constant while the photon density that until then was null begins to grow linearly.
13) Power in escape from the superficial ones of the LASER:
where is reported to the losses of the mirrors that is to the emission.
14) Coefficient of saturabile gain:
15) physical Cause of the saturation of the gain: It has had to the lack of bearers who can recombine for stimulated emission when the photonic density is elevated.
16) Answer of a LASER to the current step: Applying to a current step the density electronic the photonic concentration increases until catching up the value of threshold for the effect LASER after a time, to this point begins to grow before oscillating and then becoming stabilized itself on a value, the reason of the oscillations is that the injection of bearers realizes a population reversal, but in the moment in which it begins the stimulated emission, this vien less and therefore the stimulated emission slows down, but in such a way they increase the bearers in conduction band and it is returned in conditions of population reversal.
17) Characteristics in continuous of a LASER: The photon concentration under the threshold is 0 while over the threshold it is while the concentration of bearers under threshold is while over the threshold è .
18) Answer in frequency of a LASER:
being ed .
19) multimodali Oscillations: They are analyzed writing the installments-equations for every way m assets in the cavity.
20) Chirp: To the modulation of the density of the bearers it corresponds is a variation of amplitude of marks them of escape that a variation of the second frequency of emission la where the term is called transiente Chirp and dominates vhf while is called adiabatic Chirp and dominates to the vlves. |