Interpretation of CO2Optical Maser Experiments

Abstract

Optical maser action on a number of rotational transitions of the S w + -Zg+ vibrational band of C0 2 has been recently reported. 1 The maser lines were identified as the rotational transitions from P(12) to P(38) of the 0 0°1 -1 0°0 band and from P(22) to P(34) of the 0 0°1 -0 2°0 band. We wish to give here a simple theoretical treatment which allows us to interpret the results and especially the fact that no R-branch transitions were seen in maser oscillation. The treatment satisfactorily explains the results and leads to an interesting conclusion that for the vibrational-rotational transitions, optical maser action can be obtained on the P-branch transitions even when no inversion exists between the total population densities in the two vibrational states. Figure 1 shows pertinent parts of the energy LASER 960.8 CM 10°0-2o + RECOMBINATION AND CASCADES RAD DECAY> 720.5 CM"' (M) N RAD DECAY 667.3 CM -1 (V.S.) -00°1 (POSSIBLE ELECTRON! IMPACT EXCITATION) 2349.3 CM" 1 (V. S.) C02 Sg + 00°0 (GROUND STATE) FIG. 1. Pertinent part of energy level diagram of CO z showing the maser transitions and other optical transitions with their respective strengths (reference 2). Patel , Murray Hill, New Jersey April 1964)level diagram of C0 2 (Herzberg 2 ). The rotational levels belonging to each of the vibrational states are not shown for the sake of simplicity. The upper maser level (for both the bands) S w + (0 0°1) is optically connected to the ground state S^+(0 0°0) of CO z through strongly allowed transitions at 2349. 3 cm" 1 . The lower laser levels 2g-+ (l 0°0 and 0 2°0) both decay to the 1^(0 1*0) levels through radiative transitions at 720. 5 and 618.1 cm" 1 , respectively, and these transitions are reported to be of medium strength (reference 2). The molecules in the 1^(0 l 1 *)) levels decay through strongly allowed transitions at 667. 3 cm" 1 to the ground state of C0 2 . Thus the maser scheme looks like a four-level system. The probable excitation and decay processes are shown in Fig. 1 with their appropriate strengths as obtained from reference 2. Alternate lines in the rotational spectrum of £ w + -2g-+ bands of C0 2 are missing because of symmetry considerations for the linear and symmetric molecule C0 2 . Also, the Q-branch-i.e., AJ=0-transitions are for bidden since both the upper and the lower levels have 1 = 0.Now consider a simplified model of a vibrational level in which the rotational level populations are described by a Boltzmann distribution at a temperature T. It can be shown 2 that for a linear and symmetric molecule like CO z ,where Nj is the population density of the Jth rotational level, N=ZJJNJ, h= Planck's constant, c= velocity of light, B = rotational constant for the particular vibrational level, fe = Boltzmann's constant, gj= statistical weight for the Jth rotational level, and F(J) = energy of Jth rotational 588

HCl Chemical Laser

“…As reaction proceeds, heat is liberated and T r must rise, even though T y , a characteristic of the energy distribution in the reaction, remains near 6000°K. Maximum gain shifts to P 1 " 0 (9) at about T r = 350°K, to P^0(iO) at about T r = 400°K, and to P^ll) at about T r = 450°K. Meanwhile, the lower transitions are quenched in turn by the rise in T r .…”

“…Before it has quenched, P lm . 0 (9) appears and continues for 6 jusec. These are followed, in turn, by Pj.JlO) and then P 1 _ 0 (ll), each initiating before its predecessor is extinguished.…”

Use of relativistic electron beams for the study of chemical and rare gas laser systems

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Infrared Lasers in Nanoscale Science

“…The molecules NH 3 , OCS, CS also have quite a few laser lines in the infrared. With the SO 2 , HCN, H 2 O, many laser lines are obtained in the infrared from 30 µm up to submilimeter wavelengths [1,2] .…”

“…The carbon dioxide laser, invented by Patel [3] , operates on rotational-vibrational transitions and is still one of the most useful among all the infrared molecular lasers. In general, it is one of the most powerful lasers currently available.…”