Small signal gain

Shown in Figure 7.9 [8] is the influence variations in gas temperature and electron density have on small-signal gain, a0. This calculation was carried out for a 1-1-8, C02-N2-He mixture for a fixed-discharge EjN typical of laser operating conditions. The conditions depicted in Figure 7.9 correspond to a... 

Figure 7.9 Variation of small signal gain, a0 with gas temperature and electron density for a 1-1-8 laser mixture and reduced average electron energy of 1.5 eV [8].

WFe + CH4 / Av Small-signal gain measurements Gensel, Kompa, MacDonald 12°)... 

Cl2(NOCl) + H zjhv Small-signal gain measurements Henry et oi. 119>... 

CS2 + O2 / hv Small-signal gain measurements, infrared chemiluminescence study Hancock, Smith 204) Hancock, Morley, Smith 2i)... 

According to Eq. (83), for small-signal gain the relation In (///Jo) AN exists. One may write for the population inversion... 

Small-signal gain measurements have also been conducted for an HF chemical laser by Gensel et al. 12°). The reaction of fluorine atoms with methane has been used to pump the HF amplifier. Thus the inversion is produced exclusively by... 

Gain bandwidth Type, gain saturation Homogeneous saturation flux Decay lifetime (lower level) Inversion density Small signal gain coefficient Pump power density Output power density Laser size (diameter length) Excitation current/voltage Excitation current density Excitation power Output power Efficiency... 

If we compare the results of the distributions evaluated by Patel s formula and the actual intensity distribution of the corresponding laser transitions, there is a discrepancy in the intensity relations of the rotational components within a vibrational band. The peak intensity occurs at a higher J-value than calculated. This discrepancy is due to saturation effects. Patel s formula gives the intensity for "small signal gain", whereas the experimental peak intensity is limited by saturation effects. 

The higher saturation intensity h is, the larger becomes the maximum output intensity. The amplified intensity therefore depends on the incident intensity Im, the small signal gain Go, the saturated gain G and the saturation intensity h. If the amplifying medium is completely saturated, the gain drops to G = 1 and /out is limited to the maximum value... 

This linking of the macroscopic laser properties with the microscopic (fye ones may be enhanced by further consideration of these results. In the gain expressions Eqs. (5) and (7) neglect the reabsorption term in tuning range. Then the small signal gain per pass of the dye medium is... 

The interpretation of the saturation intensity result, Eq. (8), contains a snbtlety. In the conservative two-state system nnder discnssion, a molecule removed from the upper state by laser-stimulated emission at the rate aJe(hc/Xu) per molecule must appear in the lower state. There it itmnediately is subjected to a pump rate (per molecule) of a l j hcjX returning it to the upper state. Thus for stimulated emission to produce a reduction of the small-signal upper-state population by half, it must be at a transition rate per molecule equal to the sum of the spontaneous decay rate plus the return rate, yielding Eq. (8). This makes the saturation intensity a linear function of the pump intensity at high pump rates, the e bleaches, the small-signal gain saturates at the total inversion value AT,CTe, and the output power increases with pump rate solely through the h term in Eq. (9). 

In recent years, Sandia workers have measured the small signal gain and efficiency of the more efficient noble-gas RPL excited by fission fragments. The influence of gas temperature on the efficiency of the noble-gas RPL has been measured (Hebner, 1995). Possible applications of large, steady-state RPL have been investigated, such as power beaming to space. 

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