Experimental diagnostics of an avalanche discharge excited HgBr/HgBr2dissociation laser

IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. QE-21, NO. 8, AUGUST 1985 1271

Experimental Diagnostics of an Avalanche Discharge Excited HgBr/HgBr2 Dissociation Laser

THOMAS M. SHAY, MEMBER, IEEE, DEBRA GOOKIN, MARTIN C. JORDAN, FRANK E. HANSON, AND ERHART J. SCHIMITSCHEK

Abstract-We have investigated the effects of discharge power and nitrogen partial pressure on small signal gain, fluorescence, and discharge driver efficiency for an avalanche discharge Ne/N,/HgBr, laser. This work helps clarify the role of nitrogen in these lasers, as well as presenting the first experimental evidence for bottlenecking in the HgBr laser. An optimum intrinsic laser efficiency of 2.0 percent i s also re- ported.

I. INTRODUCTION

T HE HgBr laser has already proven to be an efficient, high-energy source of blue-green radiation [1]-[3],

[8], [9]. The laser action occurs on the B-to-X transition of the HgBr radical. Oscillation was first demonstrated by Parks [6] using electron beam excitation of an Hg/HBr/ Ar/Xe mixture. Subsequently, laser action was also observed under ArF laser photo dissociation of HgBr2 [7], avalanche discharge excitation [ 11-[5], and electron beam sustained discharge pumping [8]-[lo]. The best performance has been demonstrated by devices, based upon dissociation of HgBr, in a buffer gas consisting of rare gases and 0-10 percent nitrogen.

The two most impressive results to date are those of McGeoch et al. [8], using an e-beam sustained discharge with 10 J output energy and 2 percent wall plug efficiency, and the recent work by C. Fisher et al. [ l ] , demonstrating 1.7 percent wall plug efficiency and 2 J output using an X- ray preionized avalanche discharge, while the compara- tively simpler UV preionized discharges have recently [2] demonstrated high efficiencies and high output energies in 0.1 1 devices. The HgBr laser efficiency, output energy, and specific energy density are similar to the rare gas hal- ogen lasers. Furthermore, like the rare gas halogens [ H I , properly designed HgBr lasers may eventually be very long-lived devices. Another important advantage of the HgBr laser is that narrow bandwidth and high efficiency operation have been demonstrated for wavelengths between 495 and 505 nm [12]. Because of these characteristics, the HgBr laser promises to become an important practical blue-green laser source.

In this work, we present the first detailed experimental investigation of a UV preionized HgBr laser. Measure- ments were made of the small signal gain, upper laser level

Manuscript received June 10, 1982; revised February 15, 1985. T. M. Shay is with the Department of Electrical Engineering, Utah State

D. Gookin, M. C. Jordan, F. E. Hanson, and E. J. Schimitschek are University, Logan, UT 84322.

with the Naval Ocean Systems Center, San Diego, CA 92152.

fluorescence, energy deposited into the laser medium versus buffer gas mixture, and energy stored in the discharge driver. The results of this work are an improved under- standing of the fundamental processes of importance to the UV preionized avalanche discharge excited HgBr2/ HgBr lasers, including the clarification of the role of nitrogen. We also report the first evidence for bottlenecGng in an HgBr laser and the spectral dependence of the small signal gain.

11. EXPERIMENTAL SYSTEM The laser device utilized for these investigations was an

ultraviolet preionized avalanche discharge, constructed using Pyrex and stainless steel with viton O-rings. The electrodes were 55 cm long, separated by 3 cm, with a 1.25 cm radius of curvature. Parallel to these electrodes was a spark board with spark gaps every 2 cm. The entire laser tube was situated inside an oven whose temperature was set at 155°C in order to maintain the partial pressure of HgBr, [13] at 2.3 torr. The bulk of the laser gas mix consists of predominantly Ne with 0-10 percent N2, main- taining a total gas density of 1.33 Amagat.

The dominant production mechanisms of the HgBr(B) state are currently believed 181, 1141 to be direct electron impact excitation HgBr,:

e + HgBr, -+ HgBr (I?) + Br + e Reaction 1

and dissociative excitation transfer by nitrogen metasta- bles [15], [16]:

N,(A) + HgBr, -+ HgBr(B) + N2 + Br. Reaction 2

Other processes, such as ion-ion recombination processes and dissociative attachment [ 171, [ 181, are believed to play a lesser role in the production of upper laser level molecules 181, [ 141.

The electron impact excitation channel, which has been recently measured by Garscadden and Twist [ 191, is dominant in rare-gas (Ne or Ar)-mercury bromide mixtures [8], [ 141, while the dissociative excitation transfer channel becomes increasingly important as the partial pressure of N2 is increased in the gas mixture.

One of the intriguing features of the avalanche discharge excited HgBr lasers is the dramatic effect of nitrogen on the laser performance [3]. This is illustrated in Fig. 1, which is a plot of the measured laser output versus

0018-9197/85/0800-1271$01.00 0 1985 IEEE

1212 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. QE-21, NO. 8, AUGUST 1985

t , 1 %

9 %

ENERGY STORED (Joules)

Fig. 1. Laser wall plug efficiency. Laser output energy versus energy stored in the driver circuit. A: 1000 torr Ne; 0 : 25 torr N, and 975 torr Ne; E: 75 torr N, and 975 torr Ne. The HgBr, pressure was maintained constant at 2.3 torr. The straight dashed lines labeled 1 %, 0.9%, O S % , and 0.1 % are constant efficiency curves provided for reference.

PREIONIZER

PS 0 - 30 kV

CURRENT PROBE POINT-

LASER DISCHARGE

t

Fig. 2. HgBr laser driver circuit. C , and C, are the 38 nF energy storage capacitors, R, is a 1 Mfl charging resistor. Tis an EG&G 1102 grounded grid thyratron. Ld is the geometrical inductance of the discharge circuit and L, represents the inductance of the thyratron.

energy stored in the driver circuit with the buffer gas mixture as a parameter.

The laser wall plug efficiency peaks at 0.9 percent when the N2 pressure is 25 torr, while the device efficiency is lower for both higher and lower concentrations of N2; in particular, for a pure Ne discharge, the efficiency is considerably lower (0.25 percent). At the outset of our investigations it was not clear exactly what the reasons were for this improved performance. Two possibilities were improved kinetics due to the addition of N2 or better impedance matching to the laser excitation circuit. One of the goals of these investigations was to isolate each of these two effects.

111. DISCHARGE ENERGY AND POWER DEPOSITION In Fig. 1, the wall plug efficiency of our HgBr laser is

presented. In fast discharge lasers such as ours, the wall plug efficiency depends upon the energy transferred from the laser driver into the laser medium, as well as the fun-

damental kinetic processes of the discharge. The discharge impedance and, hence, the energy transfer efficiency is very sensitive both to the buffer gas mixture and to the energy stored in the capacitor bank. Therefore, we measured the electrical Z-V characteristics of the discharge as functions of both stored energy and buffer gas composition. This allowed us to separate impedance matching effects from performance changes due to fundamental processes in the laser medium.

Our laser is excited by the L-C inversion circuit which is shown in Fig. 2. In this circuit the energy is stored in two capacitor banks, C, and C2, each consisting of 14 2.7 nF barium titanate capacitors in parallel. C1 and C2 are charged in parallel through R, to the storage voltage V,. L, and Ld are the lumped values for the geometrical in- ductances of the devices, and are measured experimentally, while LC is a choke of a few henry. Also indicated are the points at which the voltage was probed, V,, and the current monitoring resistor, R . The operation can be

SHAY et al.: AVALANCHE DISCHARGE EXCITED HgBrlHgBr, DISSOCIATION LASER 1273

described as follows. First, the preionizer is triggered and 200 ns later, the thyratron is triggered and the circuit formed by L, and C1 starts to ring up. The potential across C1 inverts and continues on its downswing until the laser tube breaks down. Then, if the preionization was suffi- ciently intense and uniform [20], [21], a stable glow de- velops.

The important electrical characteristics of the laser discharge are the tube current and the voltage across the discharge electrodes. Our current is monitored by using R , a 50 mQ resistor. Direct measurement of the electrode potential was not convenient in our case; therefore, we measured the voltage V, (see Fig. l), which is related to the discharge voltage V, by (1).

v, = v, -t L d dildt. (1) L d represents the geometrical inductance of the laser circuit and i represents the current flowing through the discharge. Under our experimental conditions, the discharge is a purely resistive load. Therefore, if we measure L d and dildt, the discharge voltage V, can be readily calculated [2]. Furthermore, because the discharge is purely resistive when the discharge current is zero, VI is also zero. Thus, L d is given below:

L d = Vm/di/dt I i = 0. (2)

In this manner L d was measured to be approximately 25 nH. This was obtained independent of discharge conditions in over 50 independent measurements. The discharge power is readily obtained by taking the i - V, prod- uct. Finally, the energy deposited is calculated by integrating the i - V, curves.

Fig. 3 represents typical experimental discharge I-V curves. The data of Fig. 3(a) and (b) correspond to 12 kV on the driver storage bank and 2.3 torr of HgBr,, while the buffer gas mixtures are composed of 1000 torr Ne [Fig. 3(a)] and 975 torr Ne with 25 torr N2 [Fig. 3(b)]. These curves have several interesting features. First, the current full width at half maximum is identical for both curves and, in fact, the current width is always constant regardless of the buffer gas composition or energy stored in the driver. Hence, the pulse width is determined by the ring- ing frequency of the external circuit; this is because the laser discharge impedance is so low that the discharge circuit is underdamped. Next, the discharge voltage is considerably higher for the Ne/N2 mixture, indicating consid- erable cooling of the electron energy distribution by nitrogen. This is predominantly due to the anomalously large cross section for vibrational excitation of nitrogen [22]. This increased tube voltage with N2 results in a higher discharge impedance. Thus, energy is coupled more efficiently from the drive circuit, enhancing the wall plug efficiency.

Fig. 4 is a plot of the energy deposited into the laser discharge versus the energy stored in the laser driver. These measurements show the significant effects that both the laser gas composition and the energy stored in the driver have on the transfer efficiency. In a pure Ne buffer

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25 Torr N, in Ne 1 10

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(b) Fig. 3. The measured voltage and current characteristics of the HgBr laser

discharge are shown here. For both (a) and (b) the HgBr, pressure was 2.3 torr and the voltage on the storage caps (C , and C,) was 12 kV. The only difference between the two is the buffer gas mix. For the curves in (a) 1000 torr of Ne was the buffer gas, while for (b) the buffer was 975 torr Ne and 25 torr N,.

gas,. the transfer efficiency never increases above 35 percent, and it is very difficult to deposit more than, 2 J into the Ne/HgBr2 gas mix. When 25 torr of N2 is added to the Ne buffer, the transfer efficiency is enhanced considerably. It reaches nearly 50 percent at lower storage energies, and the transfer efficiency falls off less rapidly at higher driver energies compared to the previous case. Finally, with 75 torr N2 present, the transfer efficiency remains at 50 percent regardless of how hard the discharge is driven. From these results it is apparent that the intrinsic efficiency for the pure Ne buffer is much better than its wall plug efficiency, due to the low energy transfer efficiency for pure Ne, as can be seen from Fig. 5. Thus, part of the reason for the improved performance of the HgBr laser with N2 is due to the improved energy transfer efficiency obtained because N2 raises the discharge impedance. Additional evidence supporting this conclusion comes from the fact that the pulse durations of the side light fluorescence and the discharge power deposition are identical, thereby elim- inating improved discharge stability as a possible reason for improved performance. Fig. 5 also shows us that the addition of N2 also has favorable effects on the laser kinetics. In addition, the fact that the intrinsic device efficiency falls off for an increase of N2 pressure beyond 25 torr tells us that the nitrogen has two effects on the kinetics; first, for small amounts (up to 25 torr) the dominant effect is beneficial, and second, for partial pressures of N2 exceeding 25 torr, the efficiency falls off, indicating a det- rimental effect of N2 on the laser medium.


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6 -

4 -

2 -

25%

0 2 4 6 8 10 12 14 16

ENERGY STORED (Joules)

Fig. 4. Energy transfer efficiency from driver circuit into the discharge. A : 1000 torr Ne; 0 : 25 torr N, and 975 torr Ne; n: 75 torr N, and 925 torr Ne. The HgBr, pressure was maintained constant at 2.3 torr.

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0 1 1 1 1 1 1 1 1 1 1 l 1 1 1 1 1 2 3 4 5 6 7 8 9 10 11 1 2 1 3 1 4 1 5

ENERGY DEPOSITED INTO THE DISCHARGE (Joules)

Fig. 5. Intrinsic laser efficiency. Laser output energy versus the energy deposited into the discharge. A: 1000 torr Ne; .: 25 torr N, and 975 torr Ne; m: 75 torr N, and 925 torr Ne, with the HgBr, pressure constant at 2.3 torr. The two dashed curves labeled 1% and 2 % are constant efficiency curves provided for reference.

IV. OPTICAL DIAGNOSTICS Measurements of the temporal peak upper laser level

fluorescence efficiency and small signal gain versus buffer gas mix and discharge power density were performed. The results of these investigations allow us to characterize the intrinsic device performance, and to shed some light on the important fundamental processes in our device. The side light fluorescence was measured using an ITT model 4000 fast photodiode, placed perpendicular to the active length and at a distance much greater than the discharge width from the discharge. In order to be certain that our photodiode was only responding to the HgBr(B-X) fluorescence, the discharge was operated cold. Under those conditions there was no detectable photodiode signal in the 400-550 nm spectral region. Therefore, we concluded that no significant contributions came from other discharge species. The HgBr(B-X) fluorescence efficiency is presented in Fig. 6 for several different buffer gas mixes (0, 2.5, and 7.5 percent nitrogen in neon), while the discharge power density ranges from 0.4 to 1.5 MW/cm3. For

all three buffer gas mixes, we find that the fluorescence efficiency decreases with increasing discharge power density. We interpret this as evidence for electron destruction of HgBr(B) molecules. This mechanism is also consistent with the observed differences in the slopes of the three curves, due to the fact that model calculation (performed by one of the authors, F. E. Hanson) show that the electron density decreases by roughly a factor of 4 when 75 torr N2 is added to the Ne/HgBr2 gas mix. Next, exam- ining the relative fluorescence efficiency of the three gas mixes, we find the somewhat surprising (in light of the observed laser performance) result that the fluorescence efficiency is highest in the pure Ne gas mix and decreases in proportion to the nitrogen partial pressure. The discharge width increases somewhat as N2 is added to the gas mix; our measurements are independent of such geometrical changes because our detector is located at least 20 cm from our 1 cm wide discharge. Thus, the production of upper laser level molecules is less efficient in the Ne/N2/HgBr2 gas mixes than it is for the Ne/HgBr2 gas mixes. Collisional deactivation of HgBr(B) molecules is over two orders of magnitude, too slow [23]-[25] to explain these results. The decrease is almost certainly due to the fact that, when N2 is present in the discharge, a large fraction of the power goes into vibrational excitation of the nitrogen. Thus, the reason that the intrinsic efficiency of the laser decreases when the nitrogen pressure exceeds 25 torr is because of a decreased production efficiency for the upper laser level molecules. However, these fluorescence efficiency measurements do not provide us with any insight into the reasons for the intrinsic performance improvements when nitrogen is added to the gas mix. Therefore, we measured the small signal gain.

A tunable flashlamp pumped dye laser was used to probe the small signal gain of the HgBr laser discharge. Our probe pulse was 200 ns in duration with a 0.2 nm bandwidth. The dye laser beam is directed through the center of the discharge region to ensure that the gain length d is known. The intensity incident on the gain medium is Zi and the amplified output Io is detected by an ITT model

SHAY et al.: AVALANCHE DISCHARGE EXCITED HgBrlHgBr, DISSOCIATION LASER 1275

I I I I I I I I I I I I

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

DISCHARGE POWER DENSITY (MWlCC)

Fig. 6. Peak HgBr(B-X) fluorescence efficiency versus peak power deposited into the discharge for the buffer gas mixtures. A: 1000 torr Ne; 0 : 25 torr N2 and 975 torr Ne; B: 75 torr N2 and 925 torr Ne.

480 485 490 495 500 505 510

WAVELENGTH (nm)

Fig. 7. Small signal gain versus wavelength. 0 : gain measurements; the solid curve is the HgBr(B-X) emission spectrum.

4000 fast photodiode. The photodiode signal is displayed on a fast storage scope (Tektronic model 7834). The fluorescence from the HgBr discharge was at least three order of magnitude less than the amplij-ied laser output and, therefore, insignificant.

The amplification of the intensity Z traversing a gain medium of length d with small signal gain go and nonsatur- able absorption CY is given below.

where c represents the speed of light and Z, represents the medium saturation intensity. In general, solutions to (3) must be evaluated numerically. However, we can make several simplifying assumptions which allow us to obtain a closed form solution to interpret our measurements. We purposely adjusted our experimental conditions so that 1, is never greater than a few hundred watts/cm2. I, has been experimentally measured [2] to be 200 kW/cm2. There- fore, the I/Zs term in (3) can be neglected. Further- more, in our case the small signal gain is, to a ,good ap- proximation, constant during the time it takes photons to traverse the length of the laser medium ( - 2 ns). There- fore, the temporal derivative of (3) can be neglected. Making the above assumptions, (3) can be solved to yield

go - cy = lld(1n (Io/Zj)). (4)

Since the measured 121 absorption is always less than & of the small signal gain, we will neglect it. Experimen- tally, when the dye and HgBr lasers are triggered together the amplified signal Zo is measured, whereas, on alterna- tive shots only, the dye laser is fired and Zi is measured.

Fig. 7 is a plot of the measured small signal gain of the HgBr ( B - X ) transition with the measured HgBr(B-X) fluorescence plotted beneath the gain. Note that the gain spectrum follows the fluorescence spectrum as one would expect. In addition to the measurements of the small signal gain spectral dependencies, we have also measured the peak small signal gain at 502 nm versus buffer gas composition and discharge power density. These experimental results are shown in Fig. 8. The small signal gain always increases for increased power density for a given gas mix. The maximum gain measured is 9 percentlcm in the 75 torr nitrogen gas mix with high energy loading. Note that for the 25 torr N2 in Ne, the gain is slightly lower for a given power density than it is for the pure Ne mixture. The fact that the laser performance is improved for 25 torr N2, while the gain is 5 percent lower and the fluorescence is 22 percent lower, is evidence of reduced bottlenecking in the N2 mixtures.

These effects are more clearly illustrated using the fol- lowing model for the HgBr(B-X) laser system. We assume a simple two-level model Nu for the upper laser level and N L for the lower laser level; for a stimulated emission cross section o, the small signal gain is given by

go = o(N* - NL). (5 ) Noting that the HgBr(B-X) fluorescence F is proportional to Nu, we take the ratio

where C is a constant which depends upon the stimulated emission coefficient, the collection optics, detector sensi- tivity, optics efficiency, and field of view. Thus, the gain- to-fluorescence ratio is proportional to the specific inver-


I I I I I I I I I I I I I

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

DISCHARGE POWER DENSITY (MWlcc)

Fig. 8. Peak small signal gain at 502 nm versus peak power density. A: 1000 torr Ne; 0 : 975 torr Ne and 25 torr N,; .: 925 torr Ne and 75 torr N2.

0.9 I I I I I I 1 I I I I I I 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

DISCHARGE POWER DENSITY (MWlcc)

Fig. 9. Gain (at 502 nm) over fluorescence versus peak power density. A: 1000 torr Ne; 0 : 975 torr Ne and 25 torr Nz; u: 925 torr Ne and 75 torr Nz .

sion density (i.e., the population difference divided by the upper laser level population). The specific inversion density is related to the device efficiency and, hence, any improvements in it will lead to increased efficiency. Physi- cally, the specific inversion density is a measure of bottlenecking in our device. If go/F remains unchanged as the power density of the gas mix is changed, then the bottlenecking is unchanged. If golF increases, then bottlenecking has been reduced. Finally, a decrease in golF tells us that the bottlenecking is worse. The small signal gain- to-fluorescence ratio measurements are presented in Fig. 9. For all three gas mixes, the bottlenecking becomes worse as we pump harder. Also notice that the rate of increase in bottlenecking versus power density is slowed considerably by adding NZ. Both of these effects can be explained either by electron excitation of the HgBr(X) manifold or by a buildup of HgBr(X) molecules. However, our data cannot distinguish between these two processes.

Finally, the specific inversion density is increased by the addition of N2 to the gas mix. This is one of the reasons for the improved performance with N2. The reasons for this are not currently understood. The effects are too large

to be attributed to the difference in lower laser level vibrational relaxation if we use the “net removal rates” measured by Helvajian et al. [26]. Burnham [3] suggested that vibrationally excited nitrogen can collisionally dissociate the lower laser level. However, this process would require an unrealistically large cross section to be responsible for the observed effects. Finally, there has been very little consideration of the means of production of the lower laser level, other than through radiation from the HgBr(B) state, or of the vibrational excitation of the lower laser level manifold. Either of these processes might explain the observed effects.

V. SUMMARY AND CONCLUSIONS We have investigated the effects of discharge power den-

sity and buffer gas composition on the performance of an avalanche discharge excited HgBr laser. In particular, we have measured the effects of these two variables on the laser small signal gain and upper laser level production efficiency. An intrinsic device efficiency of 2.0 percent has been measured and small signal gains of up to 9 percent/ cm have been measured.

SHAY et al.: AVALANCHE DISCHARGE EXCITED HgBdHgBr, DISSOCIATION LASER 1277

Furthermore, from these investigations we now under- stand the role of nitrogen on the laser performance. Nit- grogen has several effects on the device characteristics: first, it increases the discharge energy deposition; second, there is significantly less bottlenecking in the HgBr laser system containing Nz; and, finally, the upper laser level production efficiency decreases when N2 is present in the discharge. The first two effects are responsible for the performance improvements with N2, and the latter effect results in a rolloff in device efficiency when_too much N2 i s added to the laser mix. Furthermore, our data show for the first time that bottlenecking is important in the HgBr laser system. The addition of N2 to the gas mix results in a reduction in bottlenecking. However, the reason for this is not yet understood.

Thus, our work shows that a properly impedance- matched device using an Ne/N,/HgBr, gas mix should ex- hibit 2 percent efficiency. We may even be able to do better than this by going to higher pressures in a pure Ne/HgBr2 laser system since, with a significantly higher Ne pressure, lower laser level relaxation is more rapid.

[15] R. S. F. Chang and R. Burnham, “Dissociative excitation of HgBr, by rare gas metastable atoms and N2(A3C:),” Appl. Phys. Lett., vol. 36, pp. 397-400, Mar. 15, 1980.

[I61 T. D. Dreiling and D. W. Setser, “Quenching of N2(%:) by Hg(I1) halides,” Chem. Phys. Lett., vol. 74, pp. 211-217, Sept. 1, 1980.

[17] J. Degani, M. Rokni, and S. Yatsiv, “Investigation of HgBr* excitation by X-ray sustained discharge in XeiHgBr, mixtures,” J. Chem. Phys. , V O ~ . 75, pp. 164-171, July 1, 1981.

[18] A. Garscadden and R. Twist, private communication. [20] J. I. Levatter and S.-C. Lin, “Necessary conditions for the homoge-

neous formation of pulsed avalanche discharges at high gas pressures,” J. Appl. Phys. , vol. 51, pp. 210-222, Jan. 1980.

[21] G. Herziger, R. Wollermann-Windgaase, and K. H. Banse, “On the homogenization of transverse gas discharges by preionization,” Appl.

[22] D. Spence, J. L. Mauer, and G. J. Schulz, “Measurement of total inelastic cross sections for electron impact in N2 and C02,” J. Chem. Phys., vol. 57, pp. 5516-5521, Dec. 15, 1972.

[23] H. Helvajian and C. Wittig, “Collisional quenching of HgBr Opt. Commun., vol. 30, pp. 189-192, Aug. 1979.

[24] C. Rozlo and A. Mandl, “Quenching kinetics for the HgBr (B’C,,,, C2.1rliz) states,” J. Chem. Phys. , vol. 72, pp. 541-543, Jan. 1, 1980.

Phys. , V O ~ . 24, pp. 267-272, 1981.

[25] A. Mandl, J. H. Parks, and C. Roxlo, “Collisional quenching kinetics of HgCI* and HgBr* ( B 1/2) state,” J. Chem. Phys. , vol. 72, pp. 504- 507, Jan. 1, 1980.

[26] H. Helvajian, M. Mangir, and C. Wittig, “Vibrational relaxation in HgBr (X2Ct2),” Chem. Phys. Lett., vol. 71, pp. 177-181, Apr. 1, 1980.

ACKNOWLEDGEMENT The authors wish to thank R. Krautwald for excellent

REFERENCES

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Experimental diagnostics of an avalanche discharge excited HgBr/HgBr2dissociation laser