Circuitry and calibration of solenoid actuated shutter for rapid firing of aluminum and design of ultraviolet band pass filte

Baumeister, P. W.

English

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I , 
I .I . 
I .  
THE UNIVERSITY OF ROCHESTER 
THE INSTITUTE OF OPTICS 
ROCHESTER, NEW YORK 
PROPERTIES OF MULTILAYER FILTERS 
Interim Report 
Covering the Period 
September 1, 1965 to February 28, 1966 
Research Grant No. NsG 308-63 
with 
National Aeronautics and 
Space Administration 
Washington 25, D. C. 
Principal Invesitgator: P.W. Baumeister 
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PROPERTIES OF MULTILAYER FILTERS 
Interim Report 
Covering the Period 
September 1, 1965 to February 28, 1966 
Research Grant No. NsG 308-63 
with 
National Aeronautics and 
Space Administration 
Washington 25, D.C. 
Principal Investigator: P.W. Bameis ter 
1 
ABSTMCT 
The circuitry and calibration of a solenoid-actuated 
shutter for the rapid firing of aluminum is described. An 
ultraviolet band-pass filter with an improved peak trans- 
mittance and narrower band width is designed. The filter 
consists of the conventional metal-dielectric-metal type 
filter augmented with dielectric stacks on either side of 
the metal layer: 
air (diel. stack) M (spacer) M (diel.stack)substrate. 
0 
If M represents a 150A thick aluminum layer, a computed 
peak transmittance of 80% is attained. 
Experiment a1 Program 
RAPID SHUTTERING OF A solenoid-actuated shutter was c m -  
THE ALUMINUM 
pleted and is being calibrated. As 
shown in Fig. 1, the shutter consists of a Ledex rotary 
solenoid which is "potted" inside a metal can so that it 
does not contaminate the vacuum system. The shaft of the 
solenoid passes through a rotary vacuum lead-through to the 
shutter blade. The "pump out" enables us to leak-test the 
system while it is on the bench outside of the vacuum system. 
The O-ring seals for the cover are conventional and are not 
. 
2 
shown in the Figure. 
to the electron beam and if often "sprayed" with stray elec- 
trons--hence the blade is made of a refractory metal, such 
as tantalum. The electrical leads for the solenoid are not 
shown in Fig. 1. Fig. 2 is a photograph of the shutter. 
The shutter blade is in close proximity 
ELECTRONIC 
CIRCUITRY 
The electronic circuit which automatically 
closes the shutter is depicted in the 
block diagram of Fig. 3. The details of the individual 
circuits are given 5n a previous report.' The components 
in the boxes in Fig. 3 marked "A, B, C" are new additions 
to the circuitry. 
The thickness of the aluminum film is measured by optical 
transmission monitoring. A s  aluminum is deposited on the sub- 
strate, the intensity of the 2536A radiation from the mercury 
lamp decreases. This light source--which is modulated at 
400 cps--is imaged onto a photomultiplier. As shown in 
Fig. 3, this A.C. signal eventually reaches the full-wave 
rectifier, shown in box "A". The D.C. output is thence fed 
into the "Threshold trigger'' via the cathode follower. The 
purpose of the "Threshold trigger" is to close the relay when 
the voltage drops to predetermined level. This relay in turn 
closes the solenoid shutter. This picture of the circuit is 
3 
oversimplified for purposes of illustration. In the actual 
circuit, there are many other relays and interlocks. For 
example, when the solenoid shutter closes, it also shuts off 
the high voltage to the electron gun. This is essential, since 
the aluminum is evaporating at a quite rapid rate and the 
aluminum must be conserved. There are also numerous other 
interlocks in the circuit which prevent the shutter from 
closing until the actual evaporation is underway. 
CALIBRATION OF There are some time delays in the closing 
SHUTTER 
of the shutter--not the least of which is 
the time for the relay to close. There is also appreciable 
mechanical inertia in the rotary solenoid and also the "elec- 
trical inertia" of the inductance of the solenoid. Thus 
calibration runs were made with the automatic shutter in order 
to find the "transmission obtained" in terms of the "trans- 
mission setting." Aluminum was evaporated on a set of monitor 
plates at a pressure gage reading of torr. The aluminum 
was evaporated with the electron beam (at 5 k.w. power) from 
a container in the shape of a "chalice" composed of TiB and 
BN. The aluminum-covered Suprasil test plates were removed 
from the vacuum chamber and their transmittance was measured 
on the Cary 14 spectrophotometer within 20 minutes after their 
a 
4 
I .  exposure to air. The results are shown in Table I: 
Desired 
transmittance 
at 2536A 
in X 
10 
10 
10 
10 
5 
5 
5 
TABLE I 
Plate 
number 
Transmittance 
measured at 
2500A 
in X 
8.9 1 
15.3 2 
12.4 3 
15.0 4 
14.8 5 
7.9 6 
6.9 7 
7.3 8 
With one exception, the transmission which was attained is 
larger than setting on the Varley potentiometer. 
probably due to the oxidation of the aluminum and, in fact, 
This is 
we observe that the transmission of the aluminum increases a 
day after it has been removed from the chamber. 
1-M FILTER AT 
1849A 
Several evaporations have been made to 
deposit a "1-M" type of filter for 1849A. 
The thickness of the matching stack of dielectric films of 
5 
of cryoli,e and thorium fluoride were monitored i n  re f lec t ion  
using the 1849A emission l i n e  from a mercury discharge lamp. 
The in tens i ty  of the 2536A l i n e  from the lamp is  a t  least 
ten times stronger than the 1849A l ine .  Even though a f i l ter  
was used which attenuated the 2536A line by a fac tor  of 100, 
t h i s  attenuation w a s  not suf f ic ien t  t o  evaporate the f i n a l  
matching stack of the f i l t e r .  
The procedure used t o  deposit the f i l t e r  i s  as follows: 
(1) The matching stack (composed of c ryo l i t e  and ThF4) i s  
deposited on the quartz substrate. 
s tack I” i n  Fig. 5. 
monitoring a t  1849A. Here, the small res idual  i n t ens i ty  of 
t he  2536A does not in te r fe re  with the accurate monitoring a t  
1849A. 
(2) The aluminum layer i s  deposited on top of t h i s  matching 
stack. Here, transmission monitoring i s  used to  measure i t s  
thickness. 
(3) The second matching i s  deposited on top of the aluminum. 
The thickness of the  films is determined by re f lec t ion  moni- 
tor ing off  of the aluminum a t  1849A. 
of the matching stack are deposited, the reflectance a t  1849A 
decreases. As depicted i n  Fig. 5, the reflectance shown by 
This i s  shown as “matching 
These films are deposited by re f lec t ion  
As the successive layers 
the dashed line would typically result after five layers had 
been deposited. When the full filter is completed, the 
reflectance should go to zero, as shown by the solid line in 
Fig. 5. However, the reflectance at 2536A in either case is 
essentially unaltered by the addition of the matching stacks 
and close to 85%. The net result is that the component of 
the 2536A which "leaks" through the filter in front of the 
photomultiplier becomes stronger and stronger in comparison 
with the 1849A as the "1-M" filter is completed. 
The "1-M" filters which were prepared had an adequate 
peak transmittance--ZO%--but the contrast--i. e., rejection 
was poor--of the order of 2%. Since an acceptable 1-M filter 
should have at least a 1OO:l rejection ratio of the "side 
transmittance" compared with the peak transmittance, these 
filters are not adequate. Hence, no transmittance curves 
are included for these filters. 
Theoretical Program 
OPTIMUM DESIGN OF A previous publication2 has discussed 
M D M  TYPEOF 
FILTER the "optimum" design of a "1-M" type 
of filter. In this type of filter, once the thickness and 
optical constants of the metal film and the wavelength are 
I . 
7 
. 
1 
specified, there is a systematic procedure by which a match- 
ing stack of dielectric layers is designed. 
is followed, one maximizes the radiant energy which is trans- 
mitted through the entire filter, which we have designated 
as Tmax 
filters which have two or more metal layers in them. 
effect is that the maximum transmittance of the conventional 
MDM filter can be markedly increased by adding stacks of 
dielectric matching layers to each side of the filter, as 
shown in Fig. 6 .  In this report, this latter type of filter 
is called a "transmittance-optimized" or simply a "T-optimized" 
filter. 
a previous publication,3 to the best of our knowledge there 
are no published designs for such a filter for the ultra- 
violet. 
If this procedure 
. These same design considerations can apply to 
The net 
Although this type of filter design is suggested in 
COMPARISON Fig. 7 depicts the spectral transmittance 
OF FILTERS 
of the conventional MDM type of filter. 
The dielectric layer of cryolite has a quarter-wave optical 
thickness of 3490A and the alminum metal layer is 150A in 
physical thickness. The maximurn transmittance is 43% and the 
1 
L 
full width at 2 T m m  is 375A. In actual practice, a thicker 
aluminum layer is usually used and hence the bandwidth is 
8 
slightly narrower. 
layer of aluminum is 91%. 
the MDM could be as high as (91)2 = 83% , if the MDM were 
properly matched with dielectric stacks. Thus, the maximum 
transmittance of the MDM can be nearly doubled and a narrower 
bandwidth can also be achieved. However, this advantage is 
offset by the increased complexity of the filter and the side- 
transmission bands in the neighborhood of the main pass-band. 
The maximum transmittance through a 150A 
Hence the maxhum transmittance of 
DESIGN 
PROCEDURE 
The design procedure for the augmented 
MDM filter is as follows: (1) We specify 
that the aluminum film is 15OA in thickness. Then the matching 
seack (designated as "stack 1" in Fig. 6) is designed so that 
the maximum net radiant flux is transmitted through the alumi- 
num film. 
by Costich2. 
as "stack 11" in Fig. 6) is designed for the other aluminum 
This is accomplished using graphical data computed 
(2) A similar dielectric matching stack (designated 
layer. Since one matching stack is bounded by air and the 
other stack by the quartz substrate, they are not identical, 
although the optical admittance of the two stacks is the same. 
(3) The phase shift upon reflection from inside of the "D" 
spacer layer is now computed. The optical thickness of the 
spacer layer is chosen so that a "resonance" condition is 
b 
. 
obtained a t  1, , which i s  2536A i n  t h i s  example. The e n t i r e  1 
stack i s  assembled and the resu l t ing  f i l t e r :  
I 
a i r  (H ~ 1 7  L" M D M L L (H L ) ~  quartz I 
as shown i n  Fig. 6, is  obtained. The H and L i n  t h i s  I 
design represent quarter-waves of thorium fluoride (index 
1.55 a t  2536A) and cryol i te  (index 1.36). The computed 
spec t ra l  transmittance of the resul t ing f i l t e r  i s  shown i n  
Fig. 8. Its Tmax of 80% is  close t o  the optimum of 83%. 
Due t o  the  e f f ec t  of the d i e l ec t r i c  stacks on the outside 
is re- 1 of the aluminum layers, the f u l l  width a t  y Tmax 
duced t o  80A, i n  comparison with the  f u l l  width of 375A f o r  
the  MDM shown i n  Fig. 7. Fig. 9 shows the transmittance of 
a s imilar  "T-Optimized" MDM f i l ter ,  but with a stack of lead 
f luoride and c ryo l i t e  fo r  the matching stack. The peak 
transmittance i s  64%, i n  comparison with the 80% of the f i l t e r  
in  Fig. 8. This difference i s  not due t o  an improper design 
of the matching stack, but can be a t t r ibu ted  t o  the residual 
op t ica l  absorption i n  the lead f luoride a t  2500A. 
data of Krebs,4 the opt ical  constant of lead f luoride a t  
2536A is  n = n - i k  = 2.10 - i 0.02 . Even though the 
absorption i n  the lead fluoride i s  small, the pbF2 films a re  
Using the 
10 
located in a part of the filter where the standing ratio is 
large and hence the small absorption of the films is enhanced. 
Another feature of the design shown in Fig. 9 is that the 
"side-band'' transmission peak at 3000A is much smaller than 
the comparable design in Fig. 8. This can be attributed to 
the dispersion of the refractive index of the lead fluoride. 
PROPERTIES OF The main advantage of this type of 
THE MDM F I L T E R  
"T-Optimized" design is its high peak 
transmittance. Thus, if three such filters were "ganged" 
in series so that the optical densities of the individual 
filters could be added, then a peak transmittance of (80%)3 = 
51% would be attained. However, the side transmittance peaks 
would be suppressed to an optical density of 3 or 4. However, 
the success of filter would depend upon the suppression of 
the "side-band" transmission peaks. It would be fruitful to 
study methods of achieving this side-band suppression. 
TRANSMISSION 
CONTOURS FOR 
1849A 1-M type filters for the spectral region 
Since we are designing and constructing 
near 1849A, we have computed a set of transmittance contours 
for a film 250A thick aluminum film at 1849A. The optical 
constants of the aluminum were supplied by W. R. Hunter at 
11 
the Naval Research Laboratory. These contours are similar to 
those described in a previous report for aluminum at 2536A. 
They are shown in Figs. 10 and 11. 
PERSONNEL During the previous six-month period, the fol- 
lowing persons contributed to the projects described in this 
report: 
P. W. Baumeister, Principal Investigator 
Robert L. Maier, who is working on a M.S. Thesis on 
The filters depicted in ultraviolet filters. 
Figs. 6, 7, 8 were designed by Mr. Maier and are 
part of his M.S. Thesis. He also calibrated and 
"debugged" the automatic shutter. 
References to the Literature --
1. Report of NsG 308-63 in the period 3/1/64 to 8/31/64. 
2. V. R. Costich, Ph.D. thesis, Univ. of Rochester, 1965. 
Figs. 11-14. Dr. Costich is presently preparing this 
thesis for publication. 
3. P. H. Berning and A. F. Turner, J. Opt. SOC. Am. 47, 
230 (1957). This general type of design is shown in 
Fig. 4 of this ref., although no specific details or 
examples are given. 
4 .  
5. 
6 .  
12 
G. Honcia and K. Krebs, Z. Phys k 165 202 (191 -9 1) 
Report of NsG 308-63 in the period 3/1/64 to 8/31/64, 
Fig. 3. 
P. W. Baumeister, V. R. Costich and S. C. Pieper, App. 
Opt. - 4 ,  911 (1965). 
Captions to the Figures 
1. Cross section of the solenoid-actuated shutter. This 
is not to scale. 
2. Photograph of the solenoid-actuated shutter mounted in 
the evaporator. 
and the electron gun evaporation source is exposed. 
The shutter is in the open position 
3. Block diagram of the circuitry which actuates the 
solenoid shutter. 
The threshold trigger circuit which actuates the relay 
which in turn closes the solenoid. 
Showing the spectral reflectance at various stages in 
the manufacture of a 1-M filter. 
Fig. (a) consists of the first matching stack and the 
aluminum film. In Fig. (b) the second matching stack 
has been partially completed and reflectance (shown as 
dashed line) is decreasing at 1849A as additional layers 
are added to the matching stack. 
4 .  
5. 
The partial filter in 
0 
I =  
13 
6. Design of: (a) A conventional M D M type filter using 
aluminum and a cryolite "D" spacer. 
M D M type filter in which dielectric matching stacks 
are added to each half of the filter. 
(b) A 'IT-Optimized" 
7. The computed spectral transmittance of a M D M filter 
on quartz substrate. The M layer is aluminum of 150A 
physical thickness and the "D" layer is cryolite (index 
1.36) which has a quarter-wave optical thickness of 
3490A. The net energy flow, , is also shown. 
8. The computed spectral transmittance and net energy flow, 
Y , of a 'IT-optimized" 2-M filter deposited on a quartz 
substrate, Q . The metal layer M is aluminum 150A 
in thickness and L , H represent films of cryolite 
(index 1.36) and thorium fluoride (index 1.55), re- 
spectively of quarter-wave optical thickness at 2536A. 
The matching films L' and L" represent cryolite 
films of .825 and .816 QWOT at h = 2536A, respectively, 
and the spacer layer S is 1.71 QWOT at the same wave- 
length. 
9, The transmittance T and net energy flow, Y , of a 
"T-optimized" 2-M filter deposited on a quartz sub- 
strate Q . The metal layer M is aluminum of 150A 
in thickness and L, H ,  represent films of cryolite 
c 
14 
(index 1.36) and lead fluoride (whose index is 
dispersive) respectively of quarter-wave optical 
thickness at 2536A. The layers L', L" and S 
represent cryolite films of quarter-wave optical 
thickness .848 QWOT, .85 QWOT, and 1.67 QWOT, 
respectively, at A = 2536A. 
0 
1 0 , l l .  Contours of constant transmittance (shown in per- 
cent) in the reflectance plane for an aluminum 
film of 2502 physical thickness at 1849A. The 
0 
optical constant of the aluminum is 
n = n - i k = 0.11 - i 1.95 . 
EVAPORATION 
SHUTTER 
BLADE 
LEDEX 
I 
EVAPORATION 
SOURCE 
FIG. I 
Photograph o f  t h e  so l eno id  s h u t t e r  as  i t  i s  i n s t a l l e d  
i n  t h e  vacuum chamber. The s h u t t e r  b lade  is a t  t h e  l e f t  
and t h e  electron-beam evapora t ion  source i s  a t  t h e  upper 
c e n t e r  
F I G U R E  2 
A.C. SIGNAL 
FROM 
PHOTOMULT I PLI ER 
FULL-WAVE 
RECTIFIER 
POTENTIOMETER VARLEy I 
A 
THRESHOLD 
TRIGGER 
' * 
C 
c 
c 
CATHODE I 
FOLLOWER B 
c- --n e Hg LAMP 
f 
LSUBSTRATE ON 
WHICH ALUMINUM 
FILM IS DEPOSITED 
FIG. 3 
BLOCK DIAGRAM 
OF CIRCUITRY 
. 
a 
0 1  
00 
NN 
K 
W 
0 
Q, 
3 
> 
I- 
> 
F 
5 
 
z 
W m 
z 
WRTIAL FILTER (b) 
- 
FULL FILTER 
1600 1800 2000 2200 2400 2600 
WAVELENGTH IN A 
SUBSTRATE 
ALUMINUM 
FILM 
MATCHING 
STACK I 
-- PART OF MATCHING 
STACK 11 
(b) -- 
FIG. 5 
AIR 
/ *  
i 
I .  . 
CRYOLITE 
QUARTZ SUBSTRATE 
CONVENTIONAL M D M FILTER 
AIR 
DIELECTRIC 
MATCH1 N G I STACK I1 I I I I I I 
J 
M-ALUMINUM,l50 
D 
I 
1 
I 
I i I DIELECTRIC 
QUARTZ SUBSTRATE 
"T"- OPTIMIZED 2M FILTER 
FIG. 6 
I .  
0.6 1 
I I I 1 I 
0.4 
0.2 
AMDMQ 
I 
0.2 0.3 0.4 
WAVELENGTH IN p 
FIG. 7 
0.8 
0.6 
I 1 I 1 i I I I 
Tmox = 80% 
SCALE 
CHANGE 
I I I I i 0 
020 0.23 a25 0.27 0.31 
WAVELENGTH IN p 
FIG. 8 
0.35 
0.8 
0.6 
.j 
0.4 
0.5 
C 
C 
I I I I I 
13 0.27 0.31 
WAVELENGTH IN p 
FIG. 9 
. 
F ig  IO I 
F ig  I I  


Properties of Multilayer Filters Interim Report, 1 Sep. 1965 - 28 Feb. 1966

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