1964 Correspondence 1049

TABLE I

I I Threshold Energy Threshold Energy

Pulsed (joules) @Switched (joules)

Ruby #1

Ruby #2 1' d X30 ' length

A' d X 3 3 ' length

190

250

2 2 0

312

TABLE 11

Threshold Energy Pulse Width

Q-switched (Joules) (Nanoseconds)

Ruby ' 3 3.25 inches length Sapphire etalon FX-38.4 Ruby P2 3.375 inches length

158

312

40

50 glass etalon FS-62

Drive Energ\ (Joules) fJoules)

Energy Out

Ruby $3 220 Ruby #2 400

0.100 0.060

where tt is the index of refraction of the etalon.

Our interest in the dielectric eta1011 was prompted by the need for a Q-switched laser reflector capable of withstanding repeated pulses of high peak power and was concur- rent with the recent report by D. Roess.' The

the results obtained. purpose of this communication is to report

An ordinary glass elaton with index of refraction 1.55 gives a maximum reflectance of about 17 per cent; a sapphire etalon with index of refraction 1.76 will give a maximum reflectance of about 26 per cent.

A six inch Q-switched ruby laser was operated using a glass etalon reflector for over 100,OOO laser pulses. Lse of the etalon reflector resulted in a lower threshold and narrower beam divergence. The @switched laser energy output was of the order of one joule. This extensive use resulted i n no visi- ble degradation of the etalon.

The etalon method was also used in the test of smaller Q-switched laser rods. \Vhile the measured thresholds are higher than those experienced with multilayer dielectric reflectors, the energy output in the Q- snitched mode using a spinning Porro prism switch was comparable to that ob- tained with multilayer dielectric reflector^.^

Table I shows the measured pulsed mode threshold and Q-switch mode threshold for two small diameter rubies using a glass etalon reflector and an elliptical focussing structure.

Both rubies were pumped with an FS-62 flashlamp on 3.0 inches of the ruby length. The dopant density was 0.05 per cent of chromium.

Table I1 compares the performance of two similar rubies with different etalons and flash lamp. Both rubies were 3/16 inches diameter and 0.05 per cent chromium dopant density.

I t is seen that low threshold and satis-

ning reflector technique for ruby laser pulse control." a R. C. Benson and M. R. Mirarchi. "The spin-

IEEE TRANS. ON MILITARY ELECTRONICS. vol. M I L S , pp. 13-21: January, 1964.

factory laser performance can be obtained by the correct choice of dielectric resonant reflector and pump lamp.

H. PAWEL Sewark College of Engineering

Sewark, N. J. J. R. SAXFORD J. H. ~VEXZEL

General Electric Co. Ithaca, S. Y . G. J. WOLGA

Cornell University Ithaca, S. Y .

Periodic Discontinuities in a Transmission Line

In a recent communication,1 the total reflection coefficient in the input of a line that has LV periodic small reflections is given as

where @ is the phase constant of the line. d is the distance between reflections. The maximum total input reflection I rymSxj is

N I r,l, and it occurs when = n m (nz is an integer). This assumes that the attenua- tion constant CY is zero.

I t might be of interest to show what happens to I r.vmxl if all the assumptions of the referred correspondence hold except that a #O. Then rs can be expressed as

rx = roll + (-&d&d + € - k d J @ d . . + c -n2adpn$d . . . + ,-S&d&V$d 1

Manuscript reyived March I Y . 1964. 1 J o d Perini, Periodic discontinuities in a tranr

mission line." PROC. IEEE (Correspondence), vol. 5 2 , p. 8 5 ; January. 1964.

The above equation is recognized as a geo- metric series with a common ratio ofs-m. Thus

Because the attenuation is usually given in db, the following is noted:

e-m= the power (not voltage) attenua-

e-% = Pout/Pin. tion ratio, i.e.,

a-.V2"d==antilogtO [0.1 (attenuation (in db)/unit length)X(total length of line)]

s-?'"=antilog10 IO.1 (attenuation (in db)/unit length)X(length of line segment between reflec- tions)].

If the reflections are very closely spaced or if the line is very long, Le., if for all practical purposes there are an infinite number of very small reflections, then

Z. DAVID FAKKAS Stanford Linear .kcelerator Center

Stanford University Stanford. Calif.

Mercury-Rare Gas Visible-UV Laser

A continuation of the pulsed gas laser research in mercury-rare gas combinations reported this February' has demonstrated the possibility of obtaining simultaneous laser action in the visible and ultra-violet regions in the excited states of mercury and a rare gas, when the two are combined in the same plasma tube.

Laser emission at the frequencies and for the transitions shown in Table I for -1 I1 and Hg I1 was obtained in a 5-mm bore by 150-cm cold-cathode plasma tube having mercury electrodes when filled with argon a t partial pressures in the m-Torr range.

\\'avelength selection was obtained by changing the partial pressure of argon, the temperature of the mercury, and the plasma tube peak current in a tube of fixed bore. Low pressures and high current density en- hanced excitation of the ultra-violet and short wavelength lines. Plasma tube bores as small as 3 mm have a similar effect. Laser action was observed at 4880 A in plasma

Manuscript received July 13. 1964.

'Laser action in mercury-rare gas mixture, PEW. 1 H. G. Heard, G. Makhov. and J. Pgerson.

IEEE. vol. 52. p. 414; April, 1964.