Физика/Оптика

PhD. Bimagambetov T.S.
Almaty energy and communications university, Kazakhstan

Investigation of power infrared radiation from the laser frequency

In [1,2] have been investigated internally infrared radiation in a stepwise optico-collisional (OC) settling baseline. With stepwise settlement began to settle with level 2 and then level 3 (Figure 1). Optico-collisional - absorption (emission) of a light quantum in a collision of atoms, in which there is a transition of an atom from one level to another.

In this paper, the theoretical calculated power infrared radiation depending on the intensity and duration of the laser pulse and the concentration of atoms. Excited by infrared radiation at a frequency of one laser was carried out with the settlement of the initial level of stepwise, where - angular frequency of laser light, , - the laser frequency detuning from the atomic level 1-2 and 2-3 respectively. The values of detuning frequency >> . Concentration of atoms at level 1 is approximately equal to the concentration of atoms suitable temperature. In their assessment, we assume that the lower level of the IR transitions 4 effectively depleted by stimulated emission of cascade to downstream levels of the atom (not shown), and we neglect the population of this level. As for the development of stimulated IR radiation is enough very small difference between the populations. Wavy line in the figure shows the transmission of laser energy into kinetic energy of the atom. Dependence of infrared radiation from time to time in a stepwise OS occupancy is defined [1]

. (1)

Where W^lim - limiting energy (energy at ), w₁₂ - the probability of electron transition from level 2-3. . Probability of electron transition from 1-2 is determined w₁₂=mI_LN₁, where , -cross-sectional area of the beam of infrared radiation l- the length of active medium, - frequency infrared radiation, N₁ - the concentration of atoms at level 1N₁=N,

(2)

W versus detuning is determined by the dependence on the form , put

, (3) . (1) and (2,3) we obtain

(4)

Power IR radiation

(5)

The results of theoretical calculations.

To calculate the power of infrared radiation, the parameters will take close to the experimental data [2], the frequency of infrared radiation = 4,75 ^*10¹⁴ Hz, laser pulse duration = 15 ns, =0,0314 sm², l=20 sm, the constant value m = 0,2^*10¹⁶ sm⁵/ Dzh, = 28^*10^-14 sm³/Dzh.

1. The dependence of the relative power of infrared radiation from the laser intensity.

The dependence of the relative power of infrared radiation on the laser intensity was investigated under various frequency detuning of the laser radiation and the concentration of atoms are calculated by formula (5). Figure 2 shows the dependence of the relative power of the infrared radiation of company commander on the intensity of the laser at the proving 2, 5, 10 and 20 sm^-1 and the concentrations of 5^*10¹⁵, 10^* 10¹⁵ sm^-3. When deviations of 1 sm^-1 and 5 sm^-1 dependence P of company commander on the intensity at the given concentration of atoms is linear, and - 10 and 20 sm^-1 square. This is due to the fact that the probability of transition of 2-3 w₂₃ at small detuning is very large and does not depend on laser intensity.

Power infrared radiation is determined only by the transition probability of the atom 1-2 , w₁₂ we know the probability of an atom depends on the intensity linearly. With increasing detuning w₂₃ decreases in the concentration atoms are also beginning to depend on the intensity, which explains the quadratic dependence. With increasing concentration of atoms, this dependence remains (linear and quadratic), but shifted in the direction of increasing detuning. Since an increase in the concentrations of the increasing population of level 2, which would increase the probability of transition w₂₃.

2. The dependence of the relative power of infrared radiation on the concentration of atoms.

Figure 4 shows the relative power of infrared radiation on the concentration of atoms at different detunings and laser intensity. As can be seen at small detunings (1,3) the relative power of infrared radiation on the concentration of a quadratic, and

cubic high - (2,4). As a central part of the mismatch power infrared radiation is determined only by the speed running of the transition 1 - 2 (binary collisions of atoms - a quadratic dependence), at the same time for large deviations (greater than the shock region) is still on the operating speed of the transition 2-3. Cubic dependence indicates that excited atoms in level 2 faced mainly with unexcited atoms at 1 N₁. Since the concentration of atoms at a lot of times greater than at level 2. However, we note that the collision cross section of excited atoms is not more than excited. Under experimental conditions in [2] N₂/N₁ ratio is about 1:100.
With increasing laser intensity dependence of the relative power of the infrared radiation on the concentration shifts to larger mismatch. Since with increasing intensity increases the population of level 2, which would increase the probability of

transition w₂₃.

3. The dependence of the relative power of infrared radiation on the duration of the laser pulse.

The dependence of the relative power of infrared radiation on the duration of the laser radiation obtained for different detunings and laser intensity. Atom

concentration remained constant N = 5*10¹⁵ sm^-3. As seen from Figure 5 with increasing pulse duration the relative power of infrared radiation from the top of the increases linearly and then saturates. With increasing detuning, this dependence

shifts to increase the pulse duration. As can be seen from the figure for large deviations (20 sm^-1 ) dependence of the infrared radiation from a laser radiation of this field is linear. To explain, we rewrite equation (1) and (2) for the power of the radiation . In the vicinity of the resonance transition 2-3 (with small deviations), the transition probability w₂₃ is very large and w₂₃t>>1 neglect the second term in brackets, this radiated power is independent of pulse duration. For large detunings w₂₃t<<1 and dependence is linear.

Conclusions
Thus, from the theoretical results, we can draw the following conclusions:
1. With an increase in the intensity of laser radiation power of infrared radiation depending on the detuning increases differently. For small detuning of the laser radiation from the atomic transition 1-2 dependence is linear, and at large - square. With increasing concentration of atoms leads to the tuning curve shifted upward mismatch.
2. At constant intensity dependence of the infrared radiation from the concentration at small detunings is quadratic, and for large-cubic.
3. Power versus the pulse duration has a rich character. Also depends on proving the frequency of laser radiation from the atomic transition 2-3. In the central part is saturated in a short time, with increasing frequency shifts to the pulse duration. At large detuning depends linearly on the duration of the laser pulse.

References
1. Akana BA, Bimagambetov TS Calculation of the excitation threshold energy and infrared radiation in a stepwise non-resonant population of the initial level. / / Proceedings of the Ministry of Science, Academy of Sciences of Kazakhstan.

A series of physical and mathematical. 1998, №2, P.80-84.
2. Bimagambetov T.S. Investigation of infrared radiation in pairs in two-photon and stepwise excitation of the initial level.// Vestnic KazGASA. 2008, № 2, p.232-237.

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