Spectrometer for the simultaneous measurement of intensity in various spectral regions

A polychromator in a Paschen-Runge mounting in which intensity measurements are made by means of a row of photodiodes. The spectral intensity distribution of at least two spectral regions on the Rowland circle is transmitted to the row of photodiodes by image conductors and is measured there.

REFERENCE TO RELATED APPLICATIONS 
This application claims the priority of Federal Republic of Germany 
application Ser. No. P 38 33 602.2 filed Oct. 3rd, 1988, which is 
incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
In pulsed light sources or for time-critical applications, it is generally 
necessary to examine a spectrum simultaneously in various spectral 
regions. Polychromators including concave gratings in a Paschen-Runge 
mounting are customarily employed for this purpose. These polychromators 
have adjustable slits in which masks are arranged and the light intensity 
at the location of the slit is measured by means of photodetectors. The 
photodetectors measure the respective total intensity. The information 
about spectral resolution in the vicinity of the spectral line at the slit 
is lost. 
In complicated spectra, the selected spectral lines may be interfered with 
considerably by lines from the same or another element being examined by 
the light source, and additionally, continuous radiation may contribute an 
amount to the total radiation which cannot be neglected. In these cases, 
knowledge of the spectral resolution in the vicinity of the spectral line 
is absolutely necessary since only in that way can the net line intensity 
of the selected line be determined. 
A single spectral region can be measured simultaneously by means of one row 
of photodiodes having a high spectral and time resolution and accuracy. 
However, a respective additional row of photodiodes is needed for each 
other spectral region. 
A row of photodiodes includes up to 2048 photodiodes which are arranged at 
spacings of 25 .mu.m. These photodiodes simultaneously measure the light 
intensity present at their locations. In this way, a measurement is taken 
of the spectral intensity distribution of a spectral region. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to simultaneously 
measure the spectral intensity distribution of several different spectral 
regions with one row of photodiodes. 
This is accomplished according to the invention by means of a row of 
photodiodes with which the intensity distribution of at least two spectral 
regions on the Rowland circle is transmitted at least in part by means of 
image conductors, to the row of photodiodes. With this arrangement, it is 
possible in an advantageous manner to measure the spectral intensity 
distributions of different, even widely separated spectral regions by 
means of a single row of photodiodes. 
If it is not possible to transmit all spectral regions of interest from the 
Rowland circle to the row of photodiodes by means of image conductors, the 
row of photodiodes is placed directly on the Rowland circle in the 
spectral region in which image conductors are not suitable, with the 
spectral intensity distribution of the remaining spectral regions of 
interest being transferred to the row of photodiodes by means of image 
conductors. 
For changing applications, i.e. if the spectral intensity distribution of 
different spectral regions is to be analyzed from measurement to 
measurement, it is of advantage for the image conductors to be movably 
arranged on the Rowland circle in a manner similar to the manner in which 
the photodetectors are moved in a Paschen-Runge mounting. The image 
conductors may then be arranged in such a manner in each case that the 
intensity distributions of the spectral regions of interest are imaged on 
the row of photodiodes. The image conductors are placed either manually or 
by a microprocessor controlled drive according to the spectral regions of 
interest in each case. 
To realize optimum utilization of the light intensity on the Rowland 
circle, the image conductor is advantageously configured as a cross 
section converter in which the individual fibers at the Rowland circle are 
arranged in a matrix having a rectangular cross section whose height 
corresponds to the height of the slit on the Rowland circle, each column 
of fibers of the matrix corresponding to a single photodiode and a single 
slit. Opposite the row of photodiodes, the image conductor advisably has a 
rectangular cross section corresponding to the cross section of the 
individual photodiodes. Moreover, for optimum transmission of the light 
intensity, the aperture number of each individual fiber must be considered 
so that all of the light of an image conductor can be received by the 
photodiode within its acceptance angle. 
If the image conductor, which is composed of one or a plurality of 
individual fibers, cannot be made sufficiently thin at the Rowland circle 
due to the thickness of the individual fiber, or the cross section of the 
image conductor is not small enough at the row of photodiodes, the 
transmission of light is advantageously optimized by intermediate imaging. 
The intermediate imaging enlarges the image of the entrance slit on the 
Rowland circle corresponding to the cross section of the image conductor 
and reduces the effective cross section of the image conductor at the row 
of photodiodes so that all of the light from the image conductor is 
received completely by a single photodiode of the row of photodiodes. 
Additionally, the intermediate imaging of the image of the entrance slit 
permits the selection of a different resolution from spectral region to 
spectral region. In this way it is possible, for example, to optimize the 
number of photodiodes required. 
The number of photodiodes required in the row of photodiode increases with 
the number and size of the desired spectral regions so that, under certain 
circumstances, several rows of photodiodes are required. To ensure 
simultaneous intensity measurements of all spectral regions of interest, 
these rows of photodiodes must all be actuated simultaneously.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing figures, there is shown a polychromator with a 
Paschen-Runge mounting wherein light to be analyzed is directed through an 
entrance slit 1 on a Rowland circle 2 onto a concave diffraction grating 
3, and slits 4a-4e on the Rowland circle for the spectral regions of 
interest receive the diffracted light. A row 5 of photodiodes is shown in 
two parts so as to more clearly represent image conductors and optical 
systems between slits 4b-4e and the row of photodiodes not present between 
slit 4a and the row of photodiodes. At slit 4a, the row 5 of photodiodes 
is disposed directly on the Rowland circle. The spectral regions at slits 
4b to 4e are imaged on the row of photodiodes 5 by means of respective 
image conductors 8 each of which is formed, for example, of one or a 
column of optical fibers. The image conductor 8b associated with slit 4b 
is provided with optical systems 6 and 7 for intermediate imaging since 
the grating spacing of image conductor 8b is 100 .mu.m while the diameter 
of a photodiode in the row of photodiodes is 25 .mu.m. Optical system 6 
coupling the slit 4b with the entrance cross section of the image 
conductor 8b and, the optical system 7 coupling the image conductor 8b and 
a corresponding photodiode images the exit cross section of the image 
conductor 8b on the respective photodiode. 
Alternatively to the optical systems 6 and 7, the cross sections of the 
respective image conductors 8b may be set at then respective opposite ends 
to perform the same function as the optical systems. That is, the image 
conductors 8 themselves may function as cross section converters by having 
one end 9 with a cross section equal to an acceptance cross section of the 
photodiode and an opposite end 10 with a height equal to the height of the 
spectral region on the Rowland Circle, i.e., the height of the respective 
output slit. 
The light to be analyzed enters the polychromator at entrance slit 1, and 
is diffracted at grating 3 so that the spectrum is reproduced on Rowland 
circle 2. The spectral region of interest in slit 4a is imaged directly on 
the row of photodiodes while the spectral regions in slits 4b to 4e are 
imaged on the row of photodiodes by way of image conductors 8. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.