Maksutov spectrograph for low light level researc

Harvey, G. A.

English

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U. S .  Patent No. 
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https://ntrs.nasa.gov/search.jsp?R=19710019565 2020-03-17T03:11:01+00:00Z
Inventor Gale A. Harvey 
Wampton, Va. 
Appl. No. 762,935 
Filed Sept. 26,1968 
Patented Apr. 13, 1971 
Assignee The United States of America, as 
represented by the Administrator of the 
National Aeronautics and Space 
Administration. 
2 Claim, 3 Drawing Figs. 
U.S. Cl ........................................................ 356/76 
Int. CI ......................................................... GOlj 3/40 
Field of Search ............................................ 356174, 76; 
350/162, 199,200 
References Cited 
OTHER REFERENCES 
" New Catadioptric Meniscus System" D.D. Maksutov; J. 
Qptical Society of America Vol. 34 05, May 1944 pg. 278 & 
28 1 in class 350- 200 
A Cinespectrograph for Reentry Measurements; Plakun & 
Schupp; Journal of the SMPTE; Vol. 74 0 I ;  Jan. 1965; pg. 25- 
- 27; in class 350- 199 
A Telescope Suitable for Rocket-Borne Instrumentation; 
Verdone; applied Optics; Vol. 6 03; Mar. 1967; pg. 570 & 
571. 
Primary Examiner-Ronald L. Wibert 
Assistant Examiner-V. P. McGraw 
Attorneys-Howard J. Osborn, John R. Benefiel and G .  T. Mc 
COY 
BSTRACT: A spectrograph especially suited for research 
analysis of low level sources in such areas as reentry 
spectroscopy, comprising a high efficiency transmission 
grating or prism combined with a simplified Maksutov optical 
layout, and featuring lightweight structural components and 
arrangements which minimize thermally induced misalign- 
ments and simple adjustment mechanisms for focus of the film 
surface and alignment of the optical elements. 
54 5: 
48- 
26 - 
3i574.462 
FIG. 1 " .  
FIG. 3 
INVENTOR. 
GALE A. HARVEY 
PATENTED APR 1 3 1971 
SHEET 2 OF 2 
3,574,462 
INVENTOR. 
GALE A. HARVEY 
ATTORNEYS 
This inve&n relates td  spectrography and particularly to a 
spectrograph suited for low-light-level research. Research in 
these areas presents special problems, foremost among which 
is one of a need for a great deal of sensitivity as a result of the 
extremely low levels of radiant energy encountered, and in 
addition, a reasonably broad spectral range and field-of-view 
are highly desirable. Furthermore, since field use is common, 
ease of handing in the field and freedom from a sensitivity to 
thermal changes are also prime characteristics in such a 
spectrograph. This field use also makes a capability for simple 
alignment and.adjustment of components important. Finally, 
simplicity and low cost are of course universally desirable 
3,574,462 
1 2 
~ A K S ~ T Q ~  SPECTROGRAPH The spherical mirror 22 is formed from standard telescope 
Pyrex mirror blanks, and is retained in a standard case 
The invention described herein was made by an employee aluminum mirror mount 26. 
of the United States Government and may be manufactured The film pedestal assembly 24 is comprised of a pedestal 
and used by or for the Government for governmental purposes 5 member 28 having a wall 30 corresponding to the focal 
without the Davment of any royalties thereon or therefor. surface, and the film 32 is positioned against the outer surface 
thereof by a locking ring 34, which either threadedly engages 
the member 28 as shown or has a bayonet connection 
therewith. Pedestal member 28 threadediy engages a bolt 
0 member 36 which is fastened to the corrector lens 20 by 
means of a nut 38 and a washer 40. This threaded connection 
allows precision micrometer focusing of the film surface into 
the focal surface, and for such purpose, index markings may 
be scribed onto members 28 and 36. Note that all of the 
5 primary components of both the optical and spectrographic 
systems are aligned along a common axis shown in FIG. 3 by 
the centerline passing through the focal point of the lens 20 
and mirror 22. 
qualities-in any such devices. These primary components are supported and positioned 
Prior a* efforts to supply suitable spectrographs have 20 with respect to each other by means of low thermal coefficient 
concentrated on slitless devices, since rather loose resolution of expansion structural components, These include foamed 
requirements allowed their use and a major improvement in rings 42 and 44, which may be of polystyrene, 
sensitivity was thereby had. These devices, however, were supporting the correcting lens 20 and the diffraction grating 
deficient in one or more of those areas pointed out above to be 18, respectively, which combine low coefficient of thermal 
of substantial importance. *' expansion with lightweight and high insulating properties to 
Therefore, it is an object of the present invention to provide yield a very advantageous mounting structure. 
a spectrograph having a high degree of sensitivity. These elements are positioned with respect to each other 
wide field-of-view and a broad spectral range. 46, which have low coefficients of thermal expansion. These 
It is another object to provide such a device in which the 30 rods 46 pass through all of these supporting 
effects of thermal variations on optical alignment are minimal. structure and are positioned with respect to each other by 
Yet another object to provide such a device which is easily of pairs of nuts 48 and 50, 52 and 54, and 56 and 58 
points of each element's supporting structure. Thus, and alignment of the optical elements. Still another object is to provide a lightweight instrument 35 adjustability of position with respect to both concentricity and 
focus is provided by a very simple arrangement, without easily handled in field operations. 
reading of the specification are accomplished by use of a 
Maksutov optical layout with a single corrector lens, and a parameters' 
This assembly is retained in the lightweight bakelike high efficiency fused quartz transmission diffraction grating. 40 housing 16, without any fixed connection therebetween, 
Positioning of the elements is accomplished by invar rods hence eliminating any distorting forces which might independently of the housing, and by a micrometer screw film 
pedestal. A bakelite housing and foamed be applied by the housing 16. This housing could also be of 
and thermal insulation. 
spectrograph according to the present invention. 
of the device. 
It is a further object to provide a spectrograph having both a and the mirror 22 by means of four nickel-steel or invx rods 
to provide both Of the film in the image plane engaging respective threaded of the rod on opposite 
These and Other Objects which will become apparent upon a introducing significant thermally induced in such 
retaining 
rings for the corrector lens and grating provide both lightness Or magnesium. A lens cover 60 is provided which 
45 may be utilized as a shutter mechanism. 
in the drawings, F ~ G .  is a perspective view of a From the foregoing description, it can be appreciated that 
this arrangement yields important advantages for use in the 
The extreme simplicity of the optical system, having only 
FIG. 3 is a diagram of the optical system. 50 three optical surfaces and one transmittive lens leads to both 
Referring now to the drawings and in particular to FIG. 1, high sensitivity and efficiency, and low fabrication costs while 
10 indicates generally a spectrograph according to the present still Providing adequate correction for the system. The use of 
invention. Detachably mounted thereon is a telescope fused silica in the corrector lens and diffraction grating also 
assembly 12, used to sight the source to be investigated. contributes to improved sensitivity due to the high efficiency 
access door 14 is provided in the spectrograph housing 55 of transmitting received radiation, without sacrificing spectral 
16 for film handling purposes. range. 
wen in FIG. 2, the primary components of the The independent, thermally isolated support structure 
spectrograph 10, are a dispersing element, shown a minimizesthermal distortions encountered in field use. 
transmission diffraction grating 18, an optical stop 19, a The simple adjustability of the relative position of the 
meniscus correcting lens 20, a spherical mirror 22, and film 60 various elements allows accurate alignment and focus of the 
positioning pedestal assembly 24. A layout of the optical system without introducing either greatly increased cost 0: 
system is shown in FIG. 3. weight penalties. 
The diffraction grating 18 is a high efficiency component The support structure and housing have been arranged to 
composed of optical-grade fused silica having 75 lines/m.m., both isolate thermal variations and render the device light 
and may be blazed for various wavelengths in order to obtain 65 enough for easy handling in the field. 
higher efficiency in specific ranges of interest, such as blazing I claim: 
for 3400 or 3800A for the near ultraviolet and blue, or 5461A 1. A Maksutov spectrograph comprising: 
for the visible and near infrared. As an alternative, an a housing; 
objective prism may be used as the dispersing element, formed a spherical mirror in said housing; 
also of fused silica material. These elements impart a broad 70 a Maksutov lens; 
spectral range to the instrument. a transmission dispersion element; 
The Maksutov corrector lens 20 is also fabricated from support members for said spherical mirror, said Maksutov 
optical-grade fused silica, and has radii of curvature and 
thickness to minimize chromatic and spherical aberration at at least three rods adjustably positioning and aligaing said 
the center of the field, in a manner as i s  known in the prior art. 75 mirror, lens and transmission dispersion element 
FIG. 2 is a view ofa  section taken along the longitudinal axis fieldoflow-light-level spectroscopic research. 
lens and said transmission dispersion element; 
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4 
including pairs of threaded members threadedly engaging 2. The spectrograph of claim 1 wherein said rods are 
each rod at points stradling each of said support composed of nickel-steel, said support members are 
members; composed of foamed plastic, said dispersion element is a 
diffraction grating of fused silica, pedestal 
between said lens and said pedestal member, and wherein said 
housing is 
a pedestal member located on the unreflected axis of the 
adjustably fastened to said lens and having a curved 
surface corresponding to the surface whereby sin- 
gle-frame film is molded to said curved surface of said 
pedestal member. 
Maksutov Optical system, said pedestal member being member includes a threaded pedestal support member 
Of 
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