Small Detector Array For Infrared Imaging Microscope

Abstract

An infrared imaging microscope, particularly of the type used to carry out FT-IR measurement, has a detector in the form of a small detector array of individual detector elements. The outputs of the detector elements are fed in parallel to processing means which process the output signals. The use of a small array means that the outputs can be processed without the need for complex multiplexing or perhaps no multiplexing at all thus avoiding the reduction in signal to noise ratio which is associated with large scale multiplexing. The small detector array will generally have between 3 and 100 detector elements. Typically the upper limit will be 64 and a preferred arrangement has 16 detector elements.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a divisional patent application of pending U.S. patent application Ser. No. 09 / 942,131 for a “Small Detector Array For Infrared Imaging Microscope,” filed Aug. 29, 2001, which claims priority of European Patent Application No. 00307372.3 filed on Aug. 29, 2000, the content of which is incorporated herein by reference.FIELD OF THE INVENTION[0002]This invention relates to an infrared imaging microscope particularly of the type used to carry out FT-IR measurements.BACKGROUND OF THE INVENTION[0003]A known apparatus of this type is an FT-IR microscope which is used to analyse small samples of material. The microscope has a viewing configuration and a measurement configuration. In both configurations the microscope can be used either in a transmitting mode or a reflecting mode depending upon the nature of the sample. Typically such a microscope is used in conjunction with an IR spectrophotometer. A microscope of this type ge...

AI Technical Summary

Benefits of technology

[0005]In order to reduce measurement times microscopes have been designed which incorporate large detector arrays rather than single detector elements. One such arrangement uses an integrated array of 64.times.64 liquid nitrogen cooled photovoltaic MCT detectors each having an area of 60 microns square. This array is capable of acquiring a 64.times.64 pixel image simultaneously rather than sequentially as in the system referred to above. With such an arrangement it is possible to reduce considerably the measurements times and, for example, a 128.times.128 map can be acquired in around 5 to 7 minutes. Such arrangements however are extremely expensive and typically cost more than 3 times that of a microscope which employs a single detector. Part of this increased cost is due to the cost of the detector itself which is relatively expensive and another part is attributed to the fact that the slow read out of the multiplexed detector necessitates the use of a sophisticated spectrometer technology called step-scan.

[0006]Although such large arrays offer the advantage of speed of measurement through the acquisition of many pixels in parallel, currently available devices suffer from a loss of signal / noise ratio when compared with the projected performance based on a single array element. The loss arises from inefficiencies incurred in the multiplexing needed to handle the signals from such a large number of elements. In addition, the photovoltaic technology used in these arrays results in a reduced wavelength range when compared with the photoconductive devices used as single element detectors.

[0007]The present invention is concerned with a detector array which can be used with an infrared imaging microscope and can provide the benefits of reduced measurement times without the significant increase in costs associated with the large detector arrays referred to above.

[0009]Thus the present invention proposes using in an infrared imaging microscope a relatively small detector array whose outputs are sufficiently small in number that they can be processed without the need for complex multiplexing or perhaps any multiplexing at all. Thus the microscope does not incur the reduction in signal to noise ratio which is a feature of large scale multiplexing. Such a detector array can be used in such a way as to provide relatively low measurement times without any substantial increase in cost of either the detector array or the processing circuitry needed to process the outputs of the detector elements. In addition, it becomes more practical to employ photoconductive technology for the detector elements, permitting an increased range to longer wavelength. A small detector array will typically comprise between 3 and 100 detector elements. Typically the upper limit will be 64 and a preferred arrangement will have 16.

[0019]Another aspect of the present invention provides a detector array for use in an IR microscope, said detector array comprising a plurality of individual detector elements which are disposed in spaced relationship, the spacing between adjacent elements being substantially equal to a dimension or a multiple of the dimension of a detector element. A detector array of this structure in which the detector elements are spaced apart facilitates connections to the detector elements and because, at any particular stage position, the areas viewed by the detector elements correspond to the spaces between detector elements at a previous stage position, an effective fill-in factor can be achieved. This avoids the problem of prior art array elements where the entire sample area may not be mapped because of dead areas at the junctions of adjacent detectors.

Problems solved by technology

Such arrangements however are extremely expensive and typically cost more than 3 times that of a microscope which employs a single detector.

Part of this increased cost is due to the cost of the detector itself which is relatively expensive and another part is attributed to the fact that the slow read out of the multiplexed detector necessitates the use of a sophisticated spectrometer technology called step-scan.

Although such large arrays offer the advantage of speed of measurement through the acquisition of many pixels in parallel, currently available devices suffer from a loss of signal / noise ratio when compared with the projected performance based on a single array element.

The loss arises from inefficiencies incurred in the multiplexing needed to handle the signals from such a large number of elements.

In addition, the photovoltaic technology used in these arrays results in a reduced wavelength range when compared with the photoconductive devices used as single element detectors.

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