A dual laser optical system and method is disclosed for visualization of phenomena in transport substances which induce refractive index gradients such as fluid flow and pressure and temperature gradients in fluids and gases. Two images representing mutually perpendicular components of refractive index gradients may be viewed simultaneously on screen. Two lasers having wave lengths in the visible range but separated by about 1000 angstroms are utilized to provide beams which are collimated into a beam containing components of the different wave lengths. The collimated beam is passed through a test volume of the transparent substance. The collimated beam is then separated into components of the different wave lengths and focused onto a pair of knife edges arranged mutually perpendicular to produce and project images onto the screen

Owen, R. B.

Witherow, W. K.

English

NASA Technical Reports Server

States Patent t191 
Owen et d. 
D11, 4,391,518 
WI Jul. 5, 1983 
[54] DUAL LASER OPTICAL SYSTEM AND 
METHOD FOR STUDYING FLUID FLOW 
[75] Inventors: Robert B. Owen; William K. 
[73] Assignee: The United States of America as 
Witherow, both of Huntsville, Ala. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 224,232 
[22] Filed: Jan. 12,1981 
[51] Int. CI.3 ............................................. GOlN 21/41 
[52] U.S. Cl. .................................................... 356/129 
[58] Field of Search ................. 356/128, 129, 361, 32; 
73/147 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,623,361 11/1971 Funk ................................... 356/129 
3,625,619 12/1971 Scholdstrom ....................... 356/128 
3,822,098 7/1974 Rudder et al. ...................... 356/407 
FOREIGN PATENT DOCUMENTS 
Shock Tube Laser Schlieren System”, Rev. Sci. In- 
strum., vol. 45, No. 6, Jun. 1974, pp. 773-775. 
Primary Examiner-R. A. Rosenberger 
Attorney, Agent, or Firm-’. H. Beumer; J. R. Manning; 
L. D. Wofford, Jr. 
t571 ABSTIUCT 
A dual laser optical system and method is disclosed for 
visualization of phenomena in transparent substances 
which induce refractive index gradients such as fluid 
flow and pressure and temperature gradients in fluids 
and gases. According to the invention two images 68 
and 70 representing mutually perpendicular compo- 
nents of refractive index gradients may be viewed si- 
multaneously on screen 66. Two lasers 10 and 12 having 
wave lengths in the visible range but separated by about 
lo00 angstroms are utilized to provide beams 14 and 20 
which are collimated into a beam 32 containing compo- 
nents of the different wave lengths. The collimated 
beam 32 is passed through a test volume 33 of the trans- 
parent substance. The collimated beam is then separated 
into components of the different wave lengths and fo- 
1236232 3/1967 Fed. Rep. of Germany ...... 356/129 cused on to a pair of knife edges arranged mutually 
188061 12/1966 U.S.S.R. .............................. 356/129 
199491 11/1967 U.S.S.R. .............................. 356/129 onto Screen 66. 
perpendicular to produce and project images 68 and 70 
OTHER PUBLICATIONS 
Diebold et al., “Differential Photodiode Detector for a 6 Claims, 1 Drawing Figure 
/ \ 
6526 A 
70 
https://ntrs.nasa.gov/search.jsp?R=19830021409 2020-03-22T01:16:11+00:00Z
U.S. Patent Jul. 5 ,  1983 4,391,5 18 
20 
r - 
32 - 
r 30 
z 32 
4,3913 18 
1 
DUAL LASER OPTICAL SYSTEM AND METHOD 
FOR STUDYING FLUID FLOW 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the U.S. Government and may be manufactured 
and used by or for the Government for governmental 
purposes without the payment of any royalties thereon 
or therefor. 
BACKGROUND OF THE INVENTION 
Heretofore, an optical system commonly known as 
the Schlieren system has been utilized to study density 
gradients in transparent substances by viewing refrac- 
tive index gradients. In the Schlieren method, light 
from a slit is collimated from a lens and focused onto a 
knife edge by a second lens. The text volume being 
studied is placed between the two lenses and the deflec- 
tion pattern that results is viewed on a screen placed 
behind the knife edge. The deflection is related to the 
refractive index gradients which is, in turn, related to 
the density gradient in the test volume. A more com- 
plete discussion of Schlieren apparatus may be found in 
Liepmann and Roshko, Elements of Gas Dynamics, 
Wiley & Sons, Inc., New York, 1957. However, the 
conventional system is capable of visualizing only one 
component of the index gradient at a time. 
It is advantageous to be able to observe two perpen- 
dicular components simultaneously in a dynamic situa- 
tion so that both components can be correlated. With- 
out such correlation, it is impossible to tell which physi- 
cal features are causing which phenomena. For exam- 
ple, in a moving fluid, information would be lost when 
adjustment is made from one knife edge position show- 
ing one gradient component to another knife edge posi- 
tion showing a different gradient component. The 
image changes during this time period, and this would 
be true in any dynamic situation wherein a test volume 
displays the images of the perpendicular components of 
the refractive index gradients. 
Apparatus for carrying out the method of the inven- 
tion preferably includes a helium-neon laser and an 
5 argon laser and two mutually perpendicular knife edges 
combined with conventional optical apparatus so ar- 
ranged to carry out the method according to the inven- 
tion. 
is changing its refractice index in some way. In such a ._ 
situation, it is impossible to track one particular  art of 
10 DESCRIPTION O F  THE DRAWING 
The construction designed to carry out the invention 
will be hereinafter described, together with other fea- 
tures thereof. 
The invention will be more readily understood from 
l5 a reading of the following specification and by refer- 
ence to the accompanying drawings forming a part 
thereof, wherein an example of the invention is shown 
and wherein: 
FIG. 1 is a schematic diagram illustrating an optical 
*O system and system for simultaneously visualizing per- 
pendicular components of a refractive index-density 
gradient according to the invention. 
DESCRIPTION OF PREFERRED EMBODIMENT 
Referring now to the drawing, an optical system and 
method for simultaneously visualizing perpendicular 
components of refractive index gradients is illustrated as 
including a pair of conventional lasers 10 and 12, 
3o wherein laser 10 is preferably a helium-neon laser hav- 
ing a wave length of 6328 angstroms and laser 12 is an 
argon laser having a wave length of 5145 angstroms. 
The laser beam 14 from laser 10 is directed 90" by a 
mirror 16 toward a beam splitter 18. The laser beam 20 
3s from laser 12 is reflected and directed by a mirror 22 to 
beam splitter 18 which combines beams 14 and 20 into 
beam 24 which is directed to a spatial filter 26. The 
combined beam 24 is expanded by the spatial filter at 28 
and directed to a collimating lens 30. The spatial filter 
26 may include a conventional expansion lens and pin- 
*' 
the fluid flow image and to correlate i t  with thd other 
image showing a different concentration gradient com- 
ponent. Either the density is changing, fluid motion is 
occurring, or some changes are being made in the speci- 
men during the observation period; the material speci- 
men is being stressed so that it is changing. 
SUMMARY OF THE INVENTION 
Accordingly, an important object of the present in- 
vention is to provide an optical system and method for 
visualizing perpendicular components of refractive 
index gradients simultaneously in studying fluid flow 
phenomena. 
According to the present invention, the objectives 
are accomplished by providing a pair of lasers having a 
wave length in the visible length range separated by at 
least 1,OOO angstroms, combining the beams followed by 
expanding the beams through a spatial filter whereupon 
the combined expanded beam is collimated and directed 
through the test volume. After passing through the test 
volume, the resulting beam is focused onto a transmis- 
sion grating which separates the combined beam into 
separate beams of the different wave length components 
which are focused and directed to a pair of knife edges 
arranged mutually perpendicular to each other. The 
beams and any resulting deflection of the image pattern 
are directed by means of mirrors onto a screen which 
45 
50 
55 
60 
65 
hole arrangement. The pinhole is- located at the focal 
point of collimating lens 30 which may be any conven- 
tional double convex lens. Lens 30 collimates the beam 
28 and the collimated beam 32 is directed to a mirror 34 
which reflects the beam toward a test volume 36 which 
is the subjected of analysis. 
The beam 32, passing through the test volume, is 
reflected by a mirror 38 to focus lens 40. The focus lens 
40 focuses the beam at 42 through a conventional trans- 
mission grating 44 such as a high frequency linear grat- 
ing which separates combined beam 42 into beams 46 
and 48 of the above described two different wave length 
components. Components 46 and 48 are focused on 
knife edges 50 and 52 by means of suitable mirrors 54 
and 56, respectively. Knife edges 50 and 52 are located 
at the focal point of lens 40 by adjustment in a conven- 
tional manner. The knife edges can be separately manip- 
ulated for each component beam, and by setting the 
knife edges mutually perpendicular, the desired mutu- 
ally perpendicular refractive index gradients can be 
viewed simultaneously. The resulting beams 58 and 60 
passed by the knife edges 52 and 50, respectively, are 
reflected and directed by mirrors 62 and 64 onto a 
screen 66 where images 68 and 70 of the mutually per- 
pendicular components of the refractive index are 
viewed simultaneously. 
Any suitable constant wave length lasers may be 
utilized at 10 and 12 as long as the difference in wave 
4,39 1,5 18 
4 
lengths between the two lasers is at least lo00 angstroms 2. The method of claim 1 wherein said wave lengths 
and stays in the visible wave length range. This enables are in the visible wave length range. 
grating 44 to separate the beams adequately to allow 3. The method of claim 2 wherein the difference in 
spatial arrangement of mirrors 54, 56, 62, 64, and effi- wave length between said two beams is equal to or 
cient transmission of the images on screen. Reflective 5 greater than about one-thousand angstroms. 
mirrors of any suitable type may be utilized such as flat 4. The method of claim 1 including expanding said 
surface aluminum mirrors. The lenses are illustrated as single combined beam P*or to collimating said beam. 
conventional double convex lens. 5. A dual laser optical system for producing and visu- 
B~~~ splitter 18 may be any suitable beam splitter alizing simultaneous images of perpendicular compo- 
such as a conventional refractive cube or While 10 nents of refractive index gradients in transparent sub- 
it is possible for the beam to be split by a reflective beam stances comprising: 
splitter, such a system would lead to increased optical a first laser lream having a predetermined wave 
abberations due to beam path asymmetrics. 
been described using specific terms, such description is 
for illustrative purposes only, and it is to be understood 
that changes and variations may be made without de- 
parting from the spirit or scope of the following claims. 
What is claimed is: 
1. A method of producing and visualizing simulta- 
neous images of perpendicular components of refractive 
index gradients in transparent substances comprising 
the steps of: 
length; 
15 length; 
While a preferred embodiment of the invention has a second laser beam having predetermined wave 
said wave lengths of said first and second laser beams 
being in the visible wave length range and being of 
different wave lengths from one another; 
means for combining and collimating said two laser 
beams into a single beam containing components of 
said two different wave lengths; 
for reflecting and directing said, 
collimated beam through a test volume of the sub- 
stance being studied; 
a pair of knife edges arranged mutually perpendicular 
with one another; 
grating 
nents of said collimated beam into a first separated 
beam and a second beam, respectively, of said dif- 
ferent wave lengths; 
second mirror means for focusing said separated 
beams onto said knife edges; and 
means for viewing images of the deflection patterns 
of said beams passed by said knife edges; 
third mirror means for projecting said beams onto 
said viewing means after passing said knife edge; 
and 
said viewing means producing images of a pair of 
mutually perpendicular components of refractive 
index gradients for simultaneous viewing of said 
images. 
6. The system of claim 5 wherein said first and second 
laser beams have wave lengths in the visible range, and 
said respective wave lengths are separated'by approxi- 
20 
first mirror 
providing two laser 
different wave length; 
combining and collimating said two laser beams into 
a single beam containing said two different wave 
length components; 
providing a test volume which includes said transpar- 30 
ent substance; 
passing said collimated beam through said test vol- 
ume; 
separating said collimated beam into two separate 
beams having said different wave lengths; 
providing two separate knife edges arranged mutu- 
ally perpendicular to one another; 
focusing a first of said separated beams on one of said 
knife edges and a second of said beams on the other 
of said knife edges; 
projecting light allowed to be passed by said knife 
edges onto a viewing means; and 
producing visual images of mutually perpendicular 
refractive index gradients passed by said knife 
edges on said viewing means for simultaneous -45 mately lo00 angstroms. 
viewing. 
each said beam having a 25 
for separating the individual 
35 
40 
* * * I *  
50 
55 
60 
65 


Dual laser optical system and method for studying fluid flow

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server