Spectral analyzer

A compact, lightweight, and inexpensive spectral analyzer (10) that creates a highly concentrated and collimated beam of light and that has a long optical path length that improves the analyzer's signal-to-noise ratio is disclosed. The spectral analyzer includes an optical collector assembly (12), a specimen holder (14), and an optical detector (16). The collector assembly includes a collector housing (18) having a plurality of spaced, internally reflective walls (22,24) and an exit aperture (26) through one of the walls, and a light source (20) positioned between the reflective walls. The light rays emitted from the light source are collected and collimated by the reflective walls into a highly concentrated beam of parallel light rays that is directed out of the exit aperture. The specimen holder is positioned adjacent the exit aperture of the collector for receiving the collimated beam. The collector assembly and specimen holder are positioned relative to one another so that the collimated beam is directed into the specimen holder at a pre-selected fixed angle. The specimen holder is polygonal in cross section and includes a plurality of internally reflective surfaces for reflecting the collimated beam at the pre-selected fixed angle along an optical path that is substantially longer than the specimen holder. The optical detector is positioned in or adjacent to the specimen holder for detecting the collimated beam after it has been reflected by the internally reflective surfaces of the specimen holder.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to spectral analyzers. More particularly, the 
invention relates to a lightweight and compact spectral analyzer that 
creates a highly concentrated and collimated beam of light and then 
reflects the beam along a relatively long optical path length for 
improving the analyzer's signal-to-noise ratio without the use of 
complicated and expensive optical imaging equipment. 
2. Description of the Prior Art 
Spectral analyzers are commonly used in the analysis of various types of 
gas, solid, and liquid specimens. Typical spectral analyzers include a 
specimen holder for receiving a specimen to be analyzed, a light source 
for directing light rays through the specimen holder and the specimen 
contained therein, and an optical detector for detecting the light rays 
after they have passed through the specimen and for producing 
representative signals. The detector signals are then analyzed to 
determine the effect that the specimen had upon the light rays to 
determine characteristics of the specimen such as the presence and/or 
concentration of a particular compound in the specimen. 
One significant problem associated with prior art spectral analyzers is 
that they suffer from low signal-to-noise ratios resulting from low 
detectable light levels and relatively short optical path lengths. One 
prior art solution to this problem is to focus more light energy through a 
short optical path length to increase the detectable light levels. This 
design, however, is limited by Beer-Lambert absorption problems. Other 
prior art attempts to solve this problem involve the use of complex and 
expensive imaging optical components coupled with reflective chambers. 
Although these devices have improved signal-to-noise ratios, they are too 
complicated and expensive for most applications. 
Accordingly, there is a need for a relatively compact, lightweight, and 
inexpensive spectral analyzer that achieves a relatively high 
signal-to-noise ratio without the use of complicated and expensive optical 
equipment. 
OBJECTS AND SUMMARY OF THE INVENTION 
The present invention solves the above-described problems and provides a 
distinct advance in the art of spectral analyzers. More particularly, the 
present invention provides a relatively compact, lightweight, and 
inexpensive spectral analyzer that achieves a high signal-to-noise ratio 
with a simple and cost-effective design. 
The spectral analyzer of the present invention broadly includes an optical 
collector assembly, a specimen holder, and an optical detector. The 
collector assembly includes a collector housing and a light source 
positioned within the housing. The collector housing includes a plurality 
of spaced, internally reflective walls with an exit aperture formed 
through one of the walls. The light source is positioned between the 
reflective walls so that light rays emitted therefrom reflect from the 
walls and are collected and collimated into a highly concentrated beam of 
parallel light rays that is directed out of the exit aperture. 
The specimen holder is configured for holding a liquid, gas, or solid 
sample and is positioned adjacent the exit aperture of the collector 
assembly for receiving the collimated beam. The collector assembly and 
specimen holder are positioned relative to one another so that the 
collimated beam is directed into the specimen holder at a pre-selected 
fixed angle. The specimen holder is preferably polygonal in cross section 
and includes a plurality of internally reflective surfaces for repeatedly 
reflecting the collimated beam at the pre-selected fixed angle along an 
optical path that is substantially longer than the specimen holder. 
The optical detector is positioned in or adjacent to the specimen holder 
for detecting the collimated beam after it has been reflected by the 
internally reflective surfaces of the specimen holder. The optical 
detector produces an electrical output representative of the energy level 
of the light impinging thereon. This electrical output may be fed to 
appropriate analysis equipment to determine certain characteristics of the 
sample within the specimen holder. 
By constructing a spectral analyzer as described herein, numerous 
advantages are realized. For example, by providing the spectral analyzer 
with an optical collector assembly that collimates the light rays from the 
light source into a highly concentrated beam, more light energy is focused 
through the specimen holder without the use of a higher intensity light 
source or expensive and complicated optical equipment. Additionally, by 
constructing the collector assembly and specimen holder so that the 
collimated beam enters the specimen holder at a fixed angle and then 
reflects repeatedly off the interior reflective walls of the specimen 
holder at this same fixed angle, a relatively long optical path length of 
a known length is created, thus improving the signal-to-noise ratio of the 
device without the need for expensive and complicated optical equipment. 
The combination of these features provides a spectral analyzer that is 
highly effective yet relatively compact, lightweight, and inexpensive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to FIGS. 1 and 2 of the drawing figures, a spectral analyzer 10 
constructed in accordance with a first preferred embodiment of the 
invention is illustrated. The spectral analyzer broadly includes an 
optical collector assembly 12, a specimen holder 14, and an optical 
detector 16. 
In more detail, the collector assembly 12 includes a substantially enclosed 
collector housing 18 and a light source 20 positioned therein. As 
illustrated in FIG. 1, the entire collector assembly of the first 
embodiment of the invention is preferably positioned within the confines 
of the specimen holder 14. 
The preferred collector housing 18 includes a first internal concave 
surface 22 that is spherical or elliptical in shape and an opposed second 
internal concave surface 24 that is preferably conical in shape. The first 
and second concave surfaces are coated with a reflective material so that 
the interior walls of the collector housing are highly reflective. The 
second reflective surface 24 includes an exit aperture 26 formed 
therethrough that is covered by a clear optical window 28. 
The light source 20 is positioned between the first and second concave 
reflective surfaces 22,24. The light source preferably produces light in 
the infrared spectrum and may be coupled with suitable optical filters 
(not shown) for narrowing the spectrum to a specific wavelength. Other 
suitable light sources may be used as a matter of design choice. The light 
source may be coupled with a modulator or chopping assembly for 
mechanically modulating or chopping the light beam. Similarly, the light 
source may be coupled with an electronic pulsing device for pulsing the 
light beam. 
The specimen holder 14 is preferably rectangular in cross section and 
includes a pair of generally parallel, spaced-apart sidewalls 30,32, a 
pair of generally parallel, spaced-apart end walls 34,36, and a pair of 
generally parallel, spaced-apart top and bottom walls 38,40 that together 
define an elongated, hollow fluid-receiving chamber 42 therebetween. As 
with the collector assembly, the interior surfaces of all of the walls of 
the specimen holder are coated with a reflective material so that they are 
highly reflective. 
The end wall 34 of the specimen holder 14 includes an inlet port 44 for 
introducing a specimen into the chamber 42, and the end wall 36 includes a 
corresponding outlet port 46 for discharging the specimen from the 
chamber. The specimen holder 14 may also be provided with a non-reflective 
aperture section (not shown) against which a specimen could be placed for 
permitting spectral analysis of the specimen. 
The specimen holder 14 is preferably formed of molded synthetic resin 
materials such as plastic, but may be formed of other suitable materials 
as a matter of design choice. The specimen holder illustrated in FIGS. 1 
and 2 is especially configured for the analysis of fluid specimens; 
however, it can also be used for the analysis of solid and gaseous 
samples. 
The optical detector 16 detects the collimated beam produced by the 
collector assembly 12 after it has been reflected in the specimen holder 
14. The optical detector may be positioned anywhere within or adjacent to 
the specimen holder 14 but is preferably positioned near the end wall 36 
opposite the collector assembly 12. The optical detector 16 is preferably 
a photodetector that is configured for detecting the specific wavelength 
band of light emitted by the light source 20 and for producing an 
electrical output representative of the energy level of the light 
impinging thereon. Other conventional detector devices can also be used 
with the present invention. In use, the optical detector may be coupled 
with appropriate analysis equipment that analyzes the electrical output to 
determine the characteristics of the compound within the specimen holder. 
In operation, a specimen to be analyzed is first introduced into the hollow 
chamber 42 of the specimen holder 14 through the inlet port 44. The light 
source 20 is then energized so that the light rays therefrom are directed 
toward the first and second reflective concave surfaces 22,24. The 
reflective surfaces reflect and collimate the light rays into a highly 
concentrated beam of parallel light rays as illustrated by the arrows 
within the collector assembly 12 in FIG. 1. 
The collimated beam is directed out of the exit aperture 26 of the 
collector assembly 12 and into the hollow chamber 42 of the specimen 
holder 14. The collector assembly and specimen holder are positioned 
relative to one another so that the collimated beam is directed into the 
specimen holder at a pre-selected, fixed angle of 45.degree. measured from 
the sidewalls 30,32. 
After the collimated beam enters the specimen holder 14, it impinges upon 
the internally reflective sidewall 30 and reflects toward the opposite 
sidewall 32 as illustrated by the dashed lines and arrows in FIG. 1. The 
beam continues to reflect between the sidewalls 30,32 until it impinges 
upon the interior surface of the generally perpendicular end wall 36 and 
reflects therefrom back to the sidewall 30 and toward the opposite end 
wall 34. The beam continues its path toward the end wall 34 until it 
reflects from the generally perpendicular exterior surface 48 of the 
collector assembly 12. The surface 48 reverses the direction of the beam 
and reflects it to the sidewall 30 so that it reflects between the 
sidewalls, 30,32 back toward the end wall 36 until it reaches the optical 
detector 16. 
The reflective action of the specimen holder 14 creates an optical pathway 
through the chamber 42 that is substantially longer than the length of the 
specimen holder itself. In the embodiment illustrated in FIGS. 1 and 2, 
the optical path length is approximately 3-4 times greater than the length 
of the specimen holder. Each time the light beam impinges upon one of the 
internally reflective surfaces of the specimen holder, it is reflected 
therefrom at the same fixed angle that the beam exits the reflective 
assembly. In the first embodiment of the invention, this angle is 
45.degree.. 
When the collimated beam impinges upon the optical detector 16, the 
detector detects the specific wavelength band of light and produces an 
electrical output representative of the energy level of the light 
impinging thereon. As discussed above, the optical detector may be coupled 
with appropriate analysis equipment that analyzes the electrical output to 
determine the characteristics of the compound within the specimen holder 
14. 
FIG. 3 illustrates a spectral analyzer 100 constructed in accordance with a 
second preferred embodiment of the invention in which the shape of the 
specimen holder 102 has been changed to alter the optical path of the 
collimated beam. Specifically, the specimen holder 102 includes two mating 
segments 104,106 that are generally V-shaped in cross section and that are 
joined to form an enclosed chamber 108 having end walls 110,112 each 
having a pair of generally perpendicular segments 114,116 and 118,120. In 
this embodiment, the collector assembly 122 and detector assembly 124 are 
positioned externally of the specimen holder 102 and coupled thereto with 
hollow optical passageways 126,128 to allow the collimated beam created by 
the collector assembly to reflect off of the perpendicular segments 
114-120 without interference from the collector and detector assemblies. 
The collimated beam entering the specimen holder 102 is reflected off of 
the perpendicular segments 114-120 as illustrated by the arrows and dashed 
lines in FIG. 3 until it reaches the optical detector 124. The specimen 
holder of this embodiment creates an optical path length that is 
approximately 7-8 times greater than the length of specimen holder itself. 
Although the invention has been described with reference to the preferred 
embodiment illustrated in the attached drawing figures, it is noted that 
equivalents may be employed and substitutions made herein without 
departing from the scope of the invention as recited in the claims. For 
example, although the drawing figures illustrate specific shapes for the 
specimen holder, the specimen holder may be formed in numerous shapes to 
yield an optical path of any desired length.