S for the laser linewidth at v D D chosen to calculate the return photons. In line with Figure ten, the relations involving laser intensity and average 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. Typical spontaneous emission prices vs. intensity at v D = 0, 1, 10, one hundred MHz.Atmosphere 2021, 12,12 of5. Discussions five.1. Effects of Linewidth Broadening on the Return Photons and Spot Sizes Frequently, the larger laser power forms larger peak values of intensity in the mesospheric sodium layer. In accordance with all the simulation strategy and parameters in L Section 3, the return photons are calculated for a laser power from 10 W to 60 W at v D = 0 and 10 MHz. Meanwhile, the spot sizes of the sodium laser guide star are computed. These data are listed in Table two.Table 2. Return photons and productive radii of spot sizes.Laser Power (W) Laser linewidth L v D ( MHz) Return photons F 06 ph/m2 /s Helpful radius R e f f ( m) Laser Power (W) Laser linewidth L v D ( MHz) Return photons F 06 ph/m2 /s Helpful radius R e f f ( m) 10 21.43 0.41310 0 3.56 0.426 40 0 11.26 0.413 1020 0 6.50 0.418 50 0 13.05 0.406 10 32.15 0.41330 0 9.10 0.422 60 0 15.29 0.five.36 0.ten.72 0.16.08 0.26.795 0.Based on the above data, we are able to summarize 3 benefits. Very first, linewidth broadening L is in a position to achieve probably the most return photons. We discover that the laser linewidth at v D = ten MHz L produces far more return photons than that at = 0 MHz. Compared with that at v D = 0, the L = 10 MHz increase 50.4 . Second, increments of the return photons return photons at v D increase with laser energy. For laser energy from 10 W to 60 W, calculations show that the increment of return photons goes up to 110 from 50.four . Thirdly, normally, the efficient L L radii at v D = 10 MHz are equal to those at v D = 0 MHz. Hence, the linewidth broadening approach is valuable to enhance the signal-to-noise ratio of wave-front detection in adaptive optics. It truly is well known that the strength of atmospheric turbulence can influence the intensity distribution in the laser. For the atmospheric turbulence model of Greenwood, the whole atmospheric coherent length is 15.six cm (perpendicular to ground upward for wavelength 500 nm). When the whole atmospheric coherent length is 21.6 cm, such as the atmospheric turbulence model of Mod-HV [29], the intensity distribution of the laser will trend for the larger values in space. Nonetheless, due to the fact linewidth broadening results in the reduce of peak intensity Isethionic acid sodium salt In Vitro inside the spectrum, effects of recoil will probably be weakened . five.2. Considerations of Linewidth Broadening Approach The two energy-level cycles of sodium atoms are influenced by several factors. Amongst them, depolarizations from the geomagnetic field enable a variety of sodium atoms detuning to F = 2 m = two F = three m = three cycles. To retain these two energy-level cycles, repumping ( D2b in Figure 1) is utilized to excite the sodium atoms, trapping in F = 1 ground states [2]. The laser is usually modulated having a sideband by 1.713 GHz. This sideband L linewidth need to be broadened at v D = one hundred MHz. Otherwise, the recoil will weaken the efficiency of re-pumping. The single-frequency CW laser was as soon as made use of to excite the sodium laser guide star [30]. This laser’s power 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 be a lot more efficient because of the wideAtmosphere 2021, 12,13 ofspectrum, but.
