S for the laser linewidth at v D D selected to calculate the return photons. In accordance with Figure ten, the relations amongst laser intensity and typical spontaneous emission rates are fitted byL for D = 0 L for D =MHz, MHz,1.6153 105 I R= , 1 + 0.0033I R = two.169 103 I.(20) (21)L Figure 10. Average spontaneous emission prices vs. intensity at v D = 0, 1, 10, 100 MHz.Atmosphere 2021, 12,12 of5. Discussions five.1. Effects of Linewidth Broadening on the Return Photons and Spot Sizes Normally, the higher laser power types greater peak values of intensity within the mesospheric sodium layer. In accordance using the simulation process and parameters in L Section three, the return photons are calculated for a laser energy from 10 W to 60 W at v D = 0 and ten MHz. Meanwhile, the spot sizes of your sodium laser guide star are computed. These data are listed in Table 2.Table two. Return photons and effective radii of spot sizes.Laser Energy (W) Laser linewidth L v D ( MHz) Return photons F 06 ph/m2 /s Effective radius R e f f ( m) Laser Energy (W) Laser linewidth L v D ( MHz) Return photons F 06 ph/m2 /s Successful radius R e f f ( m) ten 21.43 0.41310 0 3.56 0.426 40 0 11.26 0.413 1020 0 six.50 0.418 50 0 13.05 0.406 10 32.15 0.41330 0 9.10 0.422 60 0 15.29 0.5.36 0.10.72 0.16.08 0.26.795 0.Primarily based around the above information, we are able to summarize 3 outcomes. Very first, linewidth broadening L is capable to achieve essentially the most return photons. We find that the laser linewidth at v D = ten MHz L produces extra return photons than that at = 0 MHz. Compared with that at v D = 0, the L = ten MHz enhance 50.4 . Second, increments on the return photons return photons at v D improve with laser power. For laser energy from ten W to 60 W, calculations show that the increment of return photons goes up to 110 from 50.four . Thirdly, normally, the effective L L radii at v D = 10 MHz are equal to these at v D = 0 MHz. Hence, the linewidth broadening approach is helpful to enhance the signal-to-noise ratio of wave-front detection in adaptive optics. It is well known that the strength of atmospheric turbulence can influence the intensity distribution from the laser. For the atmospheric turbulence model of Greenwood, the entire atmospheric coherent length is 15.6 cm (perpendicular to ground upward for wavelength 500 nm). When the entire atmospheric coherent length is 21.6 cm, for instance the atmospheric turbulence model of Mod-HV [29], the intensity distribution of your laser will trend for the higher values in space. On the other hand, simply because linewidth broadening results in the decrease of peak intensity in the spectrum, effects of Phenyl acetate Acetate recoil will probably be weakened . 5.two. Considerations of Linewidth Broadening Method The two energy-level cycles of sodium atoms are influenced by a number of elements. Among them, depolarizations of your geomagnetic field allow numerous sodium atoms detuning to F = 2 m = two F = 3 m = 3 cycles. To keep these two energy-level cycles, repumping ( D2b in Figure 1) is employed to excite the sodium atoms, trapping in F = 1 ground states [2]. The laser is generally modulated using a sideband by 1.713 GHz. This sideband L linewidth should really be broadened at v D = one hundred MHz. Otherwise, the recoil will weaken the efficiency of re-pumping. The single-frequency CW laser was once applied to excite the sodium laser guide star [30]. This laser’s energy is four W, but the efficiency is low due to the 0 MHz linewidth. A modeless CW laser using a 3 GHz linewidth is believed to become additional efficient as a result of wideAtmosphere 2021, 12,13 ofspectrum, but.