Infrared optical part and measuring instrument

Details Infrared optical part and measuring instrument Infrared optical part and measuring instrument

1994-06-06

1996-10-29

Hannaher, Constantine

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

25033907, 25033911, 25033912, 2503412, G01N 2127, G02B 102

Patent

active

055699219

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to optical parts primarily for use in infrared spectral analysis and, more particularly, to an ATR (attenuated total reflectance) prism capable of measuring ATR spectra only by bringing the prism into pressure contact with a measuring object. The present invention also relates to parts such as sample plates for holding a sample to be used in measuring absorption spectra of small-quantity impurities or small portions of organic substances with a microscope type infrared spectrometer.


PRIOR ART

In a conventional infrared ATR spectrometer, first, with the use of a prism 1 as shown in FIG. 1, a sample 2, processed into a thin piece, is put into contact with a prism surface 3, on which measuring light 4 is incident. Then, upon total reflection of the light by an interface 3 between the sample and the prism, there occurs a penetration which causes an absorption unique to the sample. By measuring the spectrum of transmitted light 5 that has undergone the absorption, the sample and impurities contained therein are measured. It is to be noted that details of this method are as described in "Development of Transparent Optical Parts for Large Output CO.sub.2 Laser," by Takeo Miyata.
Conventionally, as the material of this prism 1 for infrared ATR spectral analysis, such substances as shown in Table 1 have been available. As the material of the prism 1, among other natural diamonds, the optimum one is called type IIa, which exhibits no absorption in the infrared region.


TABLE 1 __________________________________________________________________________ Characteristic Transmission Refractive Thermal region index at conductivity Material (.mu.m) 10.6 .mu.m W/cmk Problems __________________________________________________________________________ Ge 1.8-23 4.02 0.59 Transmission region narrow CdTe 0.9-30 2.69 0.06 Toxic, low in thermal conductivity GaAs 0.9-18 3.30 0.48 Transmission region narrow ZnSe 0.5-22 2.40 0.18 Transmission region narrow, liable to be damaged KBr 0.2-30 1.54 0.048 Deliquescent, liable to be damaged KCl 0.2-24 1.47 0.065 Deliquescent, liable to be damaged KRS-5 0.5-40 2.38 0.054 Deliquescent, soft, toxic Natural IIa 0.25- 2.38 20.0 Almost unavailable in large diamond size __________________________________________________________________________
However, as shown in Table 1, conventionally available substances except diamonds have had some problems such as: (1) narrow transmission region; (2) toxic; (3) liable to damage; and (4) deliquescent.
On account of the above defects, it has hitherto been quite difficult to conduct measurement in non-air-conditioned, poor-environment rooms, or at any places outdoors. Moreover, their insufficiency in durability or strength makes it difficult to push the prism into direct contact with the sample itself for measurement, which requires the sample to be formed into a thin piece and put into contact with the prism by using a special holder.
On the other hand, whereas diamonds have almost no defects in terms of material quality, the type suitable for infrared spectral analysis among diamonds is the one so called type IIa that shows no absorption in the infrared region. This type of diamond is as small in quantity as 1-2% of the total yield of natural diamonds, such that those of large size, as much as several millimeters, a size sufficient of diamond to be used as prisms, are very rare in yield and, almost unavailable in actual cases.


SUMMARY OF THE INVENTION

The present invention provides an infrared optical part and a measuring instrument employing the same which solves the above described problems and which allows ATR spectral analysis to be conducted only by pushing a prism into contact with a measuring object for measurement at any places with poor environment, measurement of structures themselves, or measurement of samples that have stuck to cloths or the like.
As a result of vigorous studies to solve the forgoing problems, the present inventors have found

REFERENCES:
patent: 5057691 (1991-10-01), Kaihara et al.
patent: 5245189 (1993-09-01), Satoh et al.

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