Optical parts and equipment using infrared athermal glasses

Optical parts and optical equipment, including lenses, mirrors and laser media made of athermal glasses having compositions comprising 0-13 mol % CdO, 9-24 mol % CdF.sub.2, 5-10 mol % LiF, 30-34.5 mol % AlF.sub.3 28-33.5 mol % PbF.sub.2, 0-4 mol % KF, 0-6.5 mol % YF.sub.3, and 0-2 mol % LaF.sub.3 and having little or no optical path length change as a function of temperature in the infrared region of 1.mu.m to 5.mu.m.

BACKGROUND OF THE INVENTION 
The present invention is related to glasses for infrared applications, 
especially infrared athermal fluoride glasses whose optical path length 
change as a function of temperature change will become practically zero 
especially in the infrared region of 1 to 5.5 .mu.m, and optical parts as 
well as optical equipment utilizing these glasses. 
In performing precise optical measurements, generally, the problem is that 
there is an optical system variation due to temperature change. As a 
typical example, the optical system may comprise a camera, especially 
camera lenses, for example, on board a space satellite, where a large 
temperature difference will occur between the portion irradiated by the 
sun light and the shaded portion. When a temperature difference occurs in 
a lens, it will appear as heterogeneity in refractive index and cause 
disorder in the image, and it MAY detrimentally affect the resolution 
capability of the camera--this has been observed in the past. Generally, 
the refractive indices of oxide system glasses rise with the rise in 
temperature. The temperature coefficient of refractive index, dn/dT is of 
the order of +10 to +2.times.10.sup.-6 /.degree. C. (Tryggve Baak, J. Opt. 
Soc. Am., 59 (1969) 851). 
In conjunction with the refractive index change, there is a linear 
expansion coefficient problem which will appear as a thickness change in 
the optical system. Although the linear expansion coefficient of quartz 
(silica) is very small, 5.times.10.sup.-7 /.degree. C., it exhibits a 
large dn/dT value of +10.times.10.sup.-6 /.degree. C. Because of this, 
attempts have been made to find a special oxide glass system to make the 
temperature coefficient of the refractive index, dn/dT, zero, and to 
account for both the refractive index temperature change and expansion. 
The development of athermal glass, whose optical path length temperature 
change, ds/dT, is zero, has been attempted by developing special oxide 
glasses (F. Reitmayer and H. Schroeder, Appl. Opt., 14 (1975) 716). 
However, these are based on interference methods utilizing a visible laser 
light; thus they are athermal glasses in the visible region. So far no 
report has been published on athermal glasses at wavelengths longer than 1 
.mu.m, which would be important for infrared cameras, etc. 
Of course, the infrared transparency of metal fluoride glasses has long 
been recognized, and efforts have been made to develop stable fluoride 
glasses to exploit this transparency. U.S. Pat. Nos. 4,537,864 and 
4,752,593, for example, report stabilized Cd--Li--A1--Pb--F glasses with 
excellent transparency in the 2-6 micron wavelength range. 
Little attention has been given, however, to the thermal properties of 
halide glasses in the infrared regime. Thus the values of dn/dT and ds/dT 
of fluoride glasses, have been reported only for ZrF.sub.4 system glasses. 
These values of dn/dT and ds/dT.sub.abs are, respectively, 
-11.times.10.sup.-6 /.degree. C. and -2.2.times.10.sup.-6 /.degree. C. 
(for ZrF.sub.4 --BaF.sub.2 --GdF.sub.3 --AlF.sub.3); and for the AlF.sub.3 
system glass example, dn/dT and ds/dT.sub.abs are -6.7.times.10.sup.-6 
/.degree. C. and Technology, Vol. 7, No. 8 (1989) p. 1256. These numbers 
do not suggest that fluoride glasses would be superior infrared athermal 
glasses, consequently, no report has been published on optical systems and 
optical parts constructed of athermal glasses operating in the infrared 
region. 
Furthermore, athermal glasses are effective as laser media where the laser 
medium refractive index temperature change due to heat generation during 
laser oscillation and the optical path length change present problems for 
the stability of the laser oscillation mode. In recent years, oxide 
glasses and fluoride glasses are being developed as media for Er, Nd, etc. 
lasers which oscillate at wavelengths longer than 1 .mu.m; however, 
presently, there has been no use of athermal glass as a laser medium at 
wavelength longer than 1 .mu.m. 
As described above, the realization of infrared athermal glasses which will 
not generate optical path length difference in the infrared region and the 
realization of optical parts and optical equipment utilizing these glasses 
are strongly desired. 
The objective of the present invention is to provide new glass compositions 
which do not change optical path length as a function of temperature 
change in the 1-5.5 .mu.m band. Furthermore, by using these glasses as 
lens or laser media for incorporation into optical parts, it is an aspect 
of the present invention to provide infrared optical equipment or optical 
parts which will not suffer degraded resolution capability due to 
temperature change in the infrared region and which will not increase in 
instability during laser performance. 
SUMMARY OF THE INVENTION 
The optical parts and optical equipment based on the present invention are 
constructed of lenses, mirrors or laser media made of athermal glasses 
having compositions comprising 0-13 mol % CdO, 9-24 mol % CdF.sub.2, 5-10 
mol % LiF, 30-34.5 mol % AlF.sub.3, 28-33.5 mol % PbF.sub.2, 0-4 mol % KF, 
0-6.5 mol % YF.sub.3, and 0-2 mol % LaF.sub.3. 
In contrast to the conventional technology focusing on the visible region, 
in the present invention, glass compositions which will have no optical 
path length change as a function of temperature change in the infrared 
region of 1 .mu.m to 5 .mu.m are provided. Furthermore, equipment 
utilizing optical parts constructed of these glasses is provided. 
According to the present invention, an infrared image tube which is 
resistive to image variation due to temperature change, an infrared 
binocular, an infrared microscope superior in resolution and stability, 
and a principal focus correction optical system for infrared telescopes 
can be constructed. In addition, if the laser medium which is exposed to 
severe temperature change or the etalon and/or partial transmitting mirror 
inside the resonator are constructed by using the infrared athermal 
glasses of the present invention, a laser with excellent thermal stability 
can be achieved.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is illustrated in detail below by reference to the 
performance examples. 
EXAMPLE 1 
A total of 50 g comprising the glass constituents shown in Table 1 below 
were weighed and melted in a platinum crucible at 950.degree. C. for 15 
minutes. The melt was then cast in a mold and annealed at 260.degree. C. 
for 1 hour. It was then cut into prism shape. Each face of the prism was 
ground-polished and the prism was used as a sample for the measurements 
set forth below. 
TABLE 1 
______________________________________ 
Glass Composition 
Glass 
Number Glass Composition (Mol %) 
______________________________________ 
CLAP 13CdO-- 9CdF.sub.2 --10LiF-- 34.5AlF.sub.3 --33.5PbF.sub.2 
CLAP-K-Y- 
24CdF.sub.2 --5LiF--32.5AlF.sub.3 --28PbF.sub.2 --4K-- 
6.5YF.sub.3 
(1) 
CLAP-K-Y- 
10CdO--14CdF.sub.2 --5LiF--30AlF.sub.3 --30.5PbF.sub.2 
(2) --4KF--6.5YF.sub.3 
CLAP-K-Y- 
12CdO--12CdF.sub.2 --6LiF--30AlF.sub.3 --30PbF.sub.2 --4KF 
La --4YF.sub.3 --2LaF.sub.3 
______________________________________ 
These four kinds of prism samples were employed in conjunction with the 
ultra violet-infrared region refractive index dispersion measurement 
equipment constructed by the optical system shown in FIG. 1 to measure the 
refractive indexes at 30 wavelengths shown in Table 2 through Table 5, in 
the wavelength range from 0.4 to 5.3 .mu.m by using the minimum deviation 
method. In this arrangement the aforementioned glass prism sample 2 was 
placed on the rotation stage 3, shown in FIG. 1 the light source 5 (Hg, 
He, CO.sub.2 bright line spectra or the combination of Pt light source and 
the absorption lines of polystyrene & trichlorobenzene, TCB) was chopped 
using the chopper 6, passed through slit 4, reflected by mirror 1a and the 
light was refracted by sample 2; and the minimum deflection position was 
measured using the InSb light receiver 9 which received the refracted 
light from mirror 1b. In this case, the lock-in amplifier 7, in 
synchronization with chopper 6, is employed to amplify the output of light 
receiver 9, and the measured results are recorded using recorder 8. 
Mirrors 1' were used for auto-collimation in obtaining the prism angle. 
The refractive index data calculated from the prism angle and the minimum 
deviation at the aforement various wavelengths for the four kinds of glass 
shown in Table 1 are given in Table 2 through Table 5. Using the 
temperature changeable sample stage as shown in FIG. 2, the temperature 
dependency of refractive index was measured. The sample prism 13 was 
placed on the brass platform 11; the temperature was measured using 
thermocouple 10 and the measured data was fed back to the electric source 
of heater 12 to control the temperature of prism sample 13 within 
+/-1.degree. C. for the temperature range employed, from room temperature 
to 200.degree. C. In this situation, by using quartz (silica) glass cover 
15, the temperature difference between the bottom portion and top portion 
of the sample prism 13 was controlled within 4.degree. C. The light for 
measurement was introduced from slit 14 to measure the refractive indices 
using the above mentioned minimum deviation method at thirty (30) 
wavelengths for temperatures up to about 200.degree. C. from room 
temperature, as shown in Table 2 through Table 5. Based on the results, 
the refractive index temperature change coefficients in air, 
dn/dT.sub.rel., were obtained according to the equation below: 
EQU dn/dT.sub.rel.=(n.sub.T1 -n.sub.T2)T.sub.1 -T.sub.2l (1) 
Where T.sub.1 and T.sub.2 denote measurement temperature and n.sub.T1 and 
n.sub.T2 are the refractive indices at the above temperatures, 
respectively. 
Next, the temperature coefficients of refractive index in vacuum are 
expressed by the equation below using the refractive index of the glass, 
n, the temperature dependency of refractive index in air, dn.sub.air /dT 
(=-9.74.times.10.sup.-7 /.degree. C.) and the refractive index of air, 
n.sub.air (=1.00027728). 
EQU dn/dT.sub.abs =n.sub.air dn/dT.sub.rel. +n(dn.sub.air //dT)(2) 
The results are shown in Table 2 and Table 3. Further, the optical path 
length temperature change, dS/dT which is important for optical design, is 
obtained by the equation below using the relation to linear thermal 
expansion coefficients. 
EQU dS/dT=dn/dT.sub.abs +a(n-1) (3) 
Glass rods of each composition shown in Table 1 were prepared and their 
linear expansion coefficients were measured and the light path length 
temperature changes were obtained from equation (3). These results are 
also shown in Table 2 through Table 5. Based on these obtained results, 
the drawn results shown in FIG. 3 through FIG. 6 were obtained. One thing 
in common from FIG. 3 through FIG. 6 is that accompanying the rise in 
temperature, the refractive index decreased; in 0.4 to 5.5 .mu.m range, 
dn/dT.sub.rel was in the range from -3 to -10.times.10.sup.-6 /.degree. C. 
Meanwhile, the optical path temperature change, dS/dT.sub.abs was close to 
zero at wavelength longer than 1 .mu.m. This phenomenon was especially 
pronounced for the respective wavelengths of various glasses as follows: 
1 to 2.4 .mu.m for CLAP (cf. FIG. 3); 1 to 5.3 .mu.m for CLAP-K-Y(1) (cf. 
FIG. 4); 1 to 2 .mu.m for CLAP-K-Y-(2) (cf. FIG. 5); and 2.1 to 4.6 .mu.m 
for CLAP-K-Y-La (cf. FIG. 6). It was especially pronounced in CLAP-K-Y(1) 
shown in FIG. 4. 
Namely, in the range from 1 .mu.m to 5.3 .mu.m, the optical path length of 
this particular family of fluoride glasses would not vary due to 
temperature change. These are the so called athermal glasses in which no 
image flickering (variation due to thermal aberration) will occur as a 
function of temperature change. The characteristics of these CLAP system 
glasses are such that they are athermal glasses in the infrared region of 
5.5 .mu.m--an important characteristic that has not been achieved in the 
past. 
Four infrared athermal glass compositions were shown in Table 1; and the 
characteristics of these infrared athermal glasses were given in Table 2 
through Table 5 and FIG. 3 through FIG. 6. The compositions of the 
infrared athermal glasses of the present invention are in the ranges as 
follows: 0-13 mol % CdO, 9-24 mol % CdF.sub.2, 5-10 mol % LiF, 30-34.5 mol 
% AlF.sub.3, 28-33.5 mol % PbF.sub.2, 0-4 mol % KF, 0-6.5 mol % YF.sub.3, 
and 0-2 mol % LaF.sub.3. 
EXAMPLE 2 
FIG. 7 shows an example of the structure of infrared image tube of the 
present invention. In this infrared image tube, a lens prepared using the 
athermal glass shown in Performance Example 1 is employed as object lens 
20. The incident infrared light 22 is focused on the photoelectric cathode 
by the infrared athermal object lens 20; and the photoelectrons 19 emitted 
by the infrared light are accelerated by electron accelerator 17 and 
converged on the fluorescence body coated anode 18. This visible 
fluorescent optical image can be observed by the eye piece 21 as visible 
image. Since the lens made of the athermal glass in Performance Example 1 
is used for the object lens 20, whose temperature is substantially raised 
by the incident light, the image tube performance, especially the image 
variation by the temperature change of the object lens, is greatly 
improved. When the aforementioned CLAP-K-Y-(1) is used for the object 
lens, the infrared images are especially stable in a wide range of 
wavelengths from 1 to 5.3 .mu.m. 
EXAMPLE 3 
FIG. 8 shows an example of the construction of infrared binoculars 
according to the present invention. The incident infrared light 22 is 
condensed on the infrared image tube 23 by the infrared region athermal 
object lens 20 and the prism 24, and it is converted to a visible image. 
This visible image is then observed by the prism 24' and the eyepiece 21. 
Similar to Performance Example 2, an infrared binocular which limits image 
variation (thermal aberration) due to temperature change was constructed 
by using the athermal glass shown in Performance Example 1 for the object 
lens 20. Preferably, by using the aforementioned athermal glass 
CLAP-K-Y-(1), a infrared binocular with good performance over a wide range 
of wavelengths can be obtained. 
EXAMPLE 4 
FIG. 9 shows an example of the construction of an infrared microscope 
according to the present invention. The incident infrared light 22 from 
the object 31 is enlarged by the infrared athermal contact-copying lens 25 
and the infrared athermal enlarger lens 26, and scanned in vertical and 
horizontal directions by the rotating polygonal mirror 27 and vibrating 
mirror 28. It is then focused and detected on the detecting element 30 by 
the infrared athermal image photographing lens 29. As described above, by 
using the athermal glass of the Performance Example 1 for the entire lens 
system, an infrared microscope was constructed which limited the image 
disturbance as a function of temperature change. For example, it is 
preferable to employ the athermal glass CLAP-K-Y-La for the lens system in 
the infrared microscope to be used for wavelength region from 2.5 to 4.5 
.mu.m. 
EXAMPLE 5 
As shown generally in FIG. 10, a concave surface mirror 33 and a focus 
correction lens system of principal focus, 32, are incorporated into the 
astronomical telescope. This principal focus correction lens system is 
composed, as shown in FIG. 11, by a plural number of lenses, 34 and 
mirror, 35. 
In the present invention, depending on the infrared wavelength region to be 
observed, the most suitable composition glasses from the infrared athermal 
glasses described in Performance Example 1 are selected for the plural 
number of lenses 34, individually. As a result, an extremely high 
precision resolution would be required and therefore, the image flickering 
(deviation) problem due to heterogeneous temperature distribution (a 
frequent problem in astronomical infrared telescopes) is drastically 
reduced. The infrared telescope of the present invention is useful in an 
environment where a temperature change often occurs due to sunlight, such 
as in space. 
EXAMPLE 6 
FIG. 12 and FIG. 13 show examples of Ar Laser resonator construction. 
Generally, in the structure of FIG. 12, the resonator is constructed by 
arranging the high reflectance efficiency mirror 37 provided with 
reflectance film 37B on the surface of the glass 37A, and the partial 
reflectance mirror 38, on either side of discharge tube 36. Partial 
reflectance mirror 38 is provided with high hardness, suitable for high 
energy laser application, by oxide system coating 38B on the surface of 
glass 38A. Using a plural number of oscillation lines, simultaneous 
oscillation is performed and then the light is dispersed by the outside 
prism 24. Meanwhile, as shown in FIG. 13, If the prism 24 and etalon 39 
are combined with non-reflecting coatings 39B on both surfaces of glass 
39A and placed inside the resonator, one wavelength single mode 
oscillation can be achieved. 
In the present invention, the infrared athermal glasses described in 
Example 1 are used to construct the partially transmitting mirror 38 in 
FIG. 12 and the partial transmitting by mirror 38 and etalon 39 in FIG. 
13. It is preferable to employ infrared athermal glass CLAP-K-Y-(1). By 
using the athermal glasses of the present invention for the partially 
transmitting mirrors and etalon, the output stability at the laser 
resonator shown in FIG. 12 is greatly improved. For the resonator shown in 
FIG. 13, in addition to the output stability improvement, the construction 
of an Ar laser without mode hopping is achieved. As described above, the 
glasses of the present invention shown in Example 1 are well suited for 
the construction of resonators that are stable against the temperature 
changes caused by the heat generated in laser oscillation. 
EXAMPLE 7 
FIG. 14 shows an example of solid laser construction of the present 
invention. The solid laser rod 41 is made of a Nd.sup.3+ doped 
CLAP-K-Y-La shown in Performanc Example 1. Namely a portion of the 
LaF.sub.3 or YF.sub.3 is replaced with NdF.sub.3 in the glass formulation 
and then the melting and casting are carried out. Using a completely 
similar procedure, the fluoride raw materials are melted. The casting of 
the melt is carried out by pouring into a hollow cylinder mold to obtain a 
cylindrical rod measuring 9 mm in diameter and 100 mm in length. Both ends 
of the rod are ground-polished to parallel surfaces and the rod is placed 
into the resonator constructed of the high reflectance mirror 37 and 
partially transmitting mirror 38 shown in FIG. 14. When the pumping light 
40 is irradiated from outside, an extremely stable 1.06 .mu.m laser light 
is obtained. In addition to Nd.sup.3+, other transition metal ions may be 
similarly doped and tested; similarly stable laser oscillations are 
achieved. For example, the laser oscillations below are achieved: 1.04 
.mu.m by Pr.sup.3+, 2.05 .mu.m by Ho.sup.3+, 1.6 .mu.m by Er.sup.3+, 1.9 
.mu.m by Tm.sup.3+, 1.02 by Yb.sup.3+, 1.1 .mu.m by Tm.sup.2+, 2.36 .mu.m 
by Dy.sup.2+, 1.62 .mu.m by Ni.sup.2+, 1.7 to 2.05 .mu.m by Co.sup.2+. The 
doping amounts of the transition metal ions are those of commonly used 
methods: for example, 1 to 5 weight %. Depending on the radiation 
wavelength, instead of CLAP-K-Y-La, other infrared athermal glasses shown 
in Performance Example 1 can be doped with rare earth ions to construct 
solid laser rods. 
EXAMPLE 8 
The Nd.sup.3+ doped CLAP-K-Y-La solid laser rod described in Example 7 is 
melted at around 400.degree. C. using a ring heater and spun into fiber 
having 200 .mu.m in outer diameter and several m in length. By fabricating 
both edges to Brewster's angle or by similarly arranging oscillation 
mirrors to its outside, laser oscillation similar to that described in 
Example 7 may be obtained. In particular, in the case of fiber type laser, 
the oscillation mode is sensitive to outside disturbances such as 
temperature change, etc. Hence when the CLAP system athermal glass is 
employed for the laser fiber matrix glass, output stability is achieved. 
Instead of the CLAP-K-Y-La, other infrared athermal glasses of the present 
invention and other transition metal ions can be employed for fiber type 
laser. 
As described above, since the glasses based on the compositions of the 
present invention have near zero optical path length change due to 
temperature from 1 .mu.m to 5.3 .mu.m, they are useful in the construction 
of optical systems which have minimal image flickering (thermal 
aberration) due to temperature change, i.e., these glasses may be used as 
object lenses in infrared image tubes, infrared binoculars, etc., where 
infrared light is directly introduced. In addition, when the glasses of 
the present invention are introduced into optical systems including lenses 
passing infrared light, improvements in resolution and stability can be 
achieved. For example, the principal focus correction optical systems used 
in infrared microscope, infrared telescope, etc., whose resolutions are 
greatly affected by temperature variation, can take advantage of the 
present invention. 
Furthermore, when the athermal glasses of the present invention are used 
for the construction of laser media, or etalons and partial transmitting 
mirrors in resonators where the temperature changes are severe, lasers 
having excellent thermal stability at radiation wavelength in the 1 to 5 
.mu.m band can be advantageously obtained. 
The present invention has been particularly shown and described with 
reference to the preferred embodiments thereof. However, it will be 
understood by those skilled in the art that various changes may be made in 
the form and details of these embodiments without departing from the true 
spirit and scope of the invention as defined by the following claims. 
TABLE 2 
__________________________________________________________________________ 
Temperature Dependency of Refractive Index and 
Light Path Length of CLAP Glass 
Wavelength 
Light 
23.degree. C. 
199.degree. C. 
dn/dT.sub.rel 
dn/dT.sub.abs 
dS/dT.sub.abs 
(.mu.m) 
Source 
R.I. 
R.I. 
(.times.10.sup.-6 /.degree.C.) 
(.times.10.sup.-6 /.degree.C.) 
(.times.10.sup.-6 /.degree.C.) 
__________________________________________________________________________ 
0.404656 
Hg 1.62937 
1.62884 
-3.01 -4.60 +6.60 
0.435835 
Hg 1.62131 
1.62054 
-4.38 -5.96 +5.09 
0.4471 He 1.61880 
1.61797 
-4.72 -6.30 +4.71 
0.5015 He 1.60987 
1.60891 
-5.45 -7.02 +3.82 
0.546074 
Hg 1.60486 
1.60382 
-5.91 -7.47 +3.28 
0.576959 
Hg 1.60198 
1.60081 
-6.65 -8.21 +2.49 
0.587561 
He 1.60113 
1.59993 
-6.82 -8.38 +2.30 
0.667815 
He 1.59607 
1.59478 
-7.33 -8.88 +1.71 
0.706519 
He 1.59428 
1.59294 
-7.61 -9.16 +1.40 
1.01398 
Hg 1.58627 
1.58486 
-8.01 -9.55 +0.87 
1.08297 
He 1.58530 
1.58383 
-8.35 -9.89 +0.51 
1.12866 
Hg 1.58468 
1.58328 
-7.95 -9.49 +0.90 
1.3622 Hg 1.58219 
1.58069 
-8.52 -10.06 +0.28 
1.52952 
Hg 1.58080 
1.57933 
-8.35 -9.89 +0.43 
1.6606 TCB 1.57979 
1.57841 
-7.84 -9.38 +0.92 
1.6932 Hg 1.57948 
1.57803 
-8.24 -9.78 +0.51 
2.1526 TCB 1.57617 
1.57475 
-8.07 -9.60 +0.64 
2.4374 TCB 1.57420 
1.57281 
-7.90 -9.43 +0.77 
3.2389 TCB 1.56728 
1.56610 
-6.70 -8.23 +1.85 
3.3036 Poly 
1.56678 
1.56548 
-7.39 -8.91 +1.16 
3.4115 TCB 1.56560 
1.56439 
-6.88 -8.40 +1.65 
3.4199 Poly 
1.56540 
1.56415 
-7.10 -8.62 +1.43 
3.5524 TCB 1.56410 
1.56283 
-7.22 -8.74 +1.28 
3.7077 TCB 1.56240 
1.56112 
-7.27 -8.79 +1.20 
3.9788 TCB 1.55943 
1.55800 
-8.13 -9.65 +0.29 
4.258 CO2 1.55606 
1.55480 
-7.16 -8.67 +1.21 
4.3769 TCB 1.55443 
1.55315 
-7.27 -8.78 +1.07 
4.5960 TCB 1.55162 
1.55043 
-6.76 -8.27 +1.53 
4.6885 TCB 1.55018 
1.54901 
-6.65 -8.16 +1.62 
5.3036 TCB 1.54047 
1.53974 
-4.15 -5.65 +3.96 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Temperature Dependency of Refractive Index and 
Light Path Length of CLAP-K-Y(1) Glass 
CLAP-K-Y(1) 
Wavelength 
Light dn/dT.sub.rel 
dn/dT.sub.abs 
dS/dT.sub.abs 
(.mu.m) 
Source 
23.degree. C. 
199.degree. C. 
(.times.10.sup.-6 /.degree.C.) 
(.times.10.sup.-6 /.degree.C.) 
(.times.10.sup.-6 /.degree.C.) 
__________________________________________________________________________ 
0.404656 
Hg 1.61873 
1.61853 
-1.13 -2.69 +7.87 
0.435835 
Hg 1.61127 
1.61091 
-2.04 -2.68 +7.75 
0.4471 He 1.60907 
1.60856 
-2.90 -5.48 +4.91 
0.5015 He 1.60074 
1.59989 
-4.83 -6.39 +3.86 
0.546074 
Hg 1.59598 
1.59503 
-5.40 -6.95 +3.21 
0.576959 
Hg 1.59329 
1.59233 
-5.45 -7.00 +3.12 
0.587561 
He 1.59263 
1.59141 
-6.93 -8.48 +1.62 
0.667815 
He 1.58792 
1.58660 
-7.50 -9.05 +0.97 
0.706519 
He 1.58617 
1.58498 
-6.76 -8.30 +1.69 
1.01398 
Hg 1.57863 
1.57715 
-8.41 -9.94 -0.08 
1.08297 
He 1.57772 
1.57631 
-8.01 -9.55 +0.293 
1.12866 
Hg 1.57711 
1.57562 
-8.47 -10.01 -0.178 
1.3622 Hg 1.57479 
1.57327 
-8.64 -10.17 - 0.378 
1.52952 
Hg 1.57341 
1.57194 
-8.35 -9.88 -0.111 
1.6606 TCB 1.57250 
1.57114 
-7.73 -9.26 +0.495 
1.6932 Hg 1.57218 
1.57070 
-8.41 -9.94 -0.192 
2.1526 TCB 1.56901 
1.56767 
-7.61 -9.14 +0.555 
2.4374 TCB 1.56709 
1.56572 
-7.78 -9.31 +0.352 
3.2389 TCB 1.56045 
1.55915 
-7.39 -8.91 +0.640 
3.3036 Poly 
1.55990 
1.55841 
-8.46 -9.98 -0.442 
3.4115 TCB 1.55887 
1.55750 
-7.78 -9.30 +0.222 
3.4199 Poly 
1.55858 
1.55713 
-8.24 -9.76 -0.244 
3.5524 TCB 1.55741 
1.55595 
-8.30 -9.82 -0.324 
3.7077 TCB 1.55564 
1.55431 
-7.56 -9.08 +0.388 
3.9788 TCB 1.55267 
1.55130 
-7.78 -9.29 +0.126 
4.258 CO2 1.54951 
1.55800 
-8.58 -10.09 -0.559 
4.3769 TCB 1.54808 
1.54664 
-8.18 -9.69 -0.353 
4.5960 TCB 1.54516 
1.54382 
-7.61 -9.11 +0.178 
4.6885 TCB 1.54386 
1.54225 
-7.44 -8.94 +0.326 
5.3036 TCB 1.53458 
1.53323 
-7.67 -9.16 -0.052 
__________________________________________________________________________ 
TABLE 4 
__________________________________________________________________________ 
Temperature Dependency of Refractive Index and 
Light Path Length of CLAP-K-Y(2) Glass 
CLAP-K-Y(2) 
Wavelength 
Light dn/dT.sub.rel 
dn/dT.sub.abs 
dS/dT.sub.abs 
(.mu.m) 
Source 
18.degree. C. 
198.degree. C. 
(.times.10.sup.-6 /.degree.C.) 
(10.sup.-6 /.degree.C.) 
(.times.10.sup.-6 /.degree.C.) 
__________________________________________________________________________ 
0.404656 
Hg 1.62293 
1.62234 
-3.28 -4.86 +5.75 
0.435835 
Hg 1.61539 
1.61452 
-4.83 -6.40 +4.07 
0.4471 He 1.61306 
1.61218 
-4.89 -6.46 +3.97 
0.5015 He 1.60465 
1.60368 
-5.39 -6.95 +3.34 
0.546074 
Hg 1.59987 
1.59880 
-5.90 -7.46 +2.74 
0.576959 
Hg 1.59717 
1.59600 
-6.50 -8.05 +2.10 
0.587561 
He 1.59637 
1.59524 
-6.28 -7.83 +2.31 
0.667815 
He 1.59156 
1.59036 
-6.67 -8.22 +1.84 
0.706519 
He 1.58978 
1.58848 
-7.22 -8.77 +1.26 
1.01398 
Hg 1.58217 
1.58084 
-7.39 -8.93 +0.97 
1.08297 
He 1.58122 
1.57980 
-7.89 -9.43 +0.45 
1.12866 
Hg 1.58062 
1.57928 
-7.44 -8.98 +0.89 
1.3622 Hg 1.57829 
1.57688 
-7.83 -9.37 + 0.746 
1.52952 
Hg 1.57698 
1.57553 
-8.06 -9.59 +0.22 
1.6606 TCB 1.57604 
1.57482 
-6.78 -8.31 +1.48 
1.6932 Hg 1.57571 
1.57434 
-7.61 -9.14 +0.65 
2.1526 TCB 1.57263 
1.57130 
-7.39 -8.92 +0.81 
2.4374 TCB 1.57077 
1.56949 
-7.11 -8.64 +1.06 
3.2389 TCB 1.56428 
1.56305 
-6.83 -8.35 +1.24 
3.3036 Poly 
1.56376 
1.56241 
-7.50 -9.02 +0.56 
3.4115 TCB 1.56279 
1.56151 
-7.11 -8.63 +0.94 
3.4199 Poly 
1.56243 
1.56119 
-6.89 -8.41 +1.15 
3.5524 TCB 1.56123 
1.56012 
-6.17 -7.69 +1.85 
3.7077 TCB 1.55951 
1.55827 
-6.89 -8.41 +1.10 
3.9788 TCB 1.55666 
1.55546 
-6.67 -8.18 +1.29 
4.258 CO2 1.55343 
1.55237 
-5.89 -7.40 +2.01 
4.3769 TCB 1.55226 
1.55104 
-6.78 -8.29 +1.10 
4.5960 TCB 1.54939 
1.54833 
-5.89 -7.40 +1.94 
4.6885 TCB 1.54812 
1.54693 
-6.61 -8.12 +1.20 
5.3036 TCB 1.53925 
1.53822 
-5.72 -7.22 +1.95 
__________________________________________________________________________ 
TABLE 5 
__________________________________________________________________________ 
Temperature Dependency of Refractive Index and 
Light Path Length of CLAP-K-Y-La Glass 
CLAP-K-Y-La 
Wavelength 
Light dn/dT.sub.rel 
dn/dT.sub.abs 
dS/dT.sub.abs 
(.mu.m) 
Source 
20.degree. C. 
200.degree. C. 
(.times.10.sup.-6 /.degree.C.) 
(.times.10.sup.-6 /.degree.C.) 
(.times.10.sup.-6 /.degree.C.) 
__________________________________________________________________________ 
0.404656 
Hg 1.62229 
1.62173 
-3.11 -4.69 +6.32 
0.435835 
Hg 1.61465 
1.61384 
-4.5 -6.07 +4.80 
0.4471 He 1.61202 
1.61105 
-5.39 -6.96 +3.86 
0.5015 He 1.60352 
1.60256 
-5.33 -6.89 +3.78 
0.546074 
Hg 1.59892 
1.59784 
-6.00 -7.56 +3.03 
0.576959 
Hg 1.59611 
1.59513 
-5.44 -6.99 +3.55 
0.587561 
He 1.59536 
1.59434 
-5.67 -7.22 +3.31 
0.667815 
He 1.59051 
1.58947 
-5.78 -6.06 +3.11 
0.706519 
He 1.58876 
1.58767 
-6.06 -7.61 +2.80 
1.01398 
Hg 1.58104 
1.57982 
-6.78 -8.31 +1.96 
1.08297 
He 1.58014 
1.57896 
-6.56 -8.10 +2.15 
1.12866 
Hg 1.57949 
1.57822 
-7.06 -8.60 +1.64 
1.3622 Hg 1.57707 
1.57593 
-6.33 -7.86 + 2.34 
1.52952 
Hg 1.57579 
1.57460 
-6.61 -8.14 +2.04 
1.6606 TCB 1.57495 
1.57365 
-7.22 -8.75 +1.41 
1.6932 Hg 1.57451 
1.57328 
-6.83 -8.36 +1.79 
2.1526 TCB 1.57152 
1.57011 
-7.83 -9.36 +0.74 
2.4374 TCB 1.56967 
1.56828 
-7.72 -9.25 +0.81 
3.2389 TCB 1.56319 
1.56175 
-8.00 -9.52 +0.43 
3.3036 Poly 
1.56265 
1.56128 
-7.61 -9.13 +0.81 
3.4115 TCB 1.56151 
1.56027 
-6.87 -8.39 +1.53 
3.4199 Poly 
1.56139 
1.56002 
-7.61 -9.13 +0.79 
3.5524 TCB 1.56016 
1.55883 
-7.39 -8.91 +0.99 
3.7077 TCB 1.55852 
1.55709 
-7.94 -9.46 +0.41 
3.9788 TCB 1.55561 
1.55421 
-7.78 -9.29 +0.53 
4.258 CO2 1.55242 
1.55111 
-7.28 -8.79 +0.97 
4.3769 TCB 1.55128 
1.54982 
-8.11 -9.62 +0.12 
4.5960 TCB 1.54833 
1.54697 
-7.56 -9.07 +0.62 
4.6885 TCB 1.54705 
1.54581 
-6.89 -8.40 +1.26 
5.3036 TCB 1.53831 
1.53712 
-6.61 -8.10 +1.41 
__________________________________________________________________________