GB2255200A - Prismatic probe head for attenuated total reflection spectroscopy - Google Patents
Prismatic probe head for attenuated total reflection spectroscopy Download PDFInfo
- Publication number
- GB2255200A GB2255200A GB9208843A GB9208843A GB2255200A GB 2255200 A GB2255200 A GB 2255200A GB 9208843 A GB9208843 A GB 9208843A GB 9208843 A GB9208843 A GB 9208843A GB 2255200 A GB2255200 A GB 2255200A
- Authority
- GB
- United Kingdom
- Prior art keywords
- probe head
- attenuated total
- optical spectroscopy
- chamfered
- radiation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/55—Specular reflectivity
- G01N21/552—Attenuated total reflection
Abstract
Apparatus for use in optical spectroscopy comprises an input fibre (21) for launching by way of a collimating lens (22) radiation towards a chamfered input surface (23) of a probe head (24) of sapphire and having at least five surfaces (25-29) exposable to a sample under test and a chamfered exit surface (30) positioned to direct said radiation towards a further lens (31) and an output fibre (32).
Description
OPTICAL PROBE HEADS
This invention relates to probe heads and, in particular, to probe heads utilising the mechanism of attenuated total reflectance for use in infra-red spectroscopy.
Attenuated Total Reflectance (ATR) crystals use the total internal reflectance to effect an interaction between a sample and beams of radiation of wavelengths suitable for infra-red spectroscopy.
Total internal reflection occurs when the crystal material is optically denser (i.e. has a greater refractive index) than the surrounding medium, provided that the angle of incidence a1 fulfills a certain condition.
The invention will now be particularly described with reference to the accompanying drawings, in which:
Figure 1 is an explanatory diagram;
Figure 2 is a series of graphs showing the variation of
penetration depth with incident angle,
refractive index and wavelength;
Figure 3 is a diagrammatic representation of a section
through an ATR head in accordance with a
specific embodiment of the invention; and
Figure 4 shows one form of apparatus envisaged by the
invention.
Figure 1 is an explanatory diagram which shows radiation incident at an angle a1 on an interface between an attenuated total reflectance crystal of refractive index n1 and a sample of refractive index n2. The penetration of the evanescent wave at an interface is given by
provided that sinai > n2/nl. If sinai < = n2/nl, then total internal reflection does not take place. Instead the ray is transmitted out of the crystal in accordance with Snell's law (n sinai = n2 sln2).
Typical samples may have indices in the region 1.3-1.5. For these, the minimum interface angle which will produce an acceptable penetration depth is dependent on the material used for the ATR crystal. Conventionally, high refractive index substances are used, such as zinc selenide, zinc sulphide, silicon or germanium. However, the mechanical and toxic qualities of these materials make them unsuitable for use in probe heads.
Referring now to Figure 2 of the drawings, a wide variety of different graphs can be constructed showing the variation of penetration depth with wavelength, angle, refractive indices etc. The series of plots shows the penetration depths obtained in sapphire against the refractive index of a sample under test for different values of al, n1 and A.
Sapphire possesses superior mechanical properties and is non-toxic. However, the minimum interface angle which will produce an acceptable penetration depth is 650. Below this angle, only samples with very low indices will exhibit total internal reflection.
For angles 650 and above total internal reflection may occur. The penetration depth, however, is such that several reflections (at least 4) are necessary to produce overall pathlengths large enough for good quality spectra.
Due to these requirements, traditional ATR crystal shapes are not suitable for sapphire.
The internal angles of an octagon are 135". If a light ray is reflected internally between faces, this corresponds to a1 = 67.50. Thus suitable sapphire ATR crystals may be based on the geometry of an octagon.
A four-reflection crystal would accommodate parallel input and output beams. However, these will necessarily be very close to the sides of the crystal, making the mounting of both the launching optics and the crystal itself very difficult unless a very large crystal is used. We have found that this problem may be overcome by using a five-reflection crystal, desirably, with chamfered input and output faces.
According to the present invention there is provided a probe head for use in attenuated total reflectance optical spectroscopy incorporating a prism having surfaces adapted to provide at least five interfaces with a sample of a material under test at which substantially total internal reflection of a beam of radiation may take place successively.
Figure 3 shows diagrammatically the path followed by an incident beam of radiation I which is refracted at an input face 10 and totally internally reflected at five probe head-sample interfaces 11-15 before being refracted at an output surface 16.
If the input and output face angles are suitably determined, the input and output rays can be deflected to be parallel.
By controlling the distance L between the first reflection and the chamfered faces, the relative displacement of the exit beam and the entrance beams is controlled.
Five reflections are sufficient to give an acceptable total path length in the region 1-5pm of the infra-red.
Figure 4 is an isometric view of a practical embodiment of the apparatus. Radiation 20 from an input optical fibre 21 passes by way of a collimating lens 22 to the input face 23 of- a probe head 24. Reflections take place internally at surfaces 25-29, after which the beam passes by way of exit surface 30 to a further lens 31 and output fibre32.
The chamfered faces allow the dimensions of the crystal to be minimised and matched to the size of the coupling optics.
Furthermore, the reflecting faces can be cut into a basic cylinder shaped crystal, facilitating airtight mounting and sealing of the crystal.
Claims (6)
1. A probe head for use in attenuated total reflectance optical spectroscopy incorporating a prism having surfaces adapted to provide at least five interfaces with a sample of a material under test at which substantially total internal reflection of a beam of radiation may take place successively.
2. A probe head for use in attenuated total reflectance optical spectroscopy as claimed in claim 1 having chamfered input and output faces for said beam of radiation.
3. A probe head for use in attenuated total reflectance optical spectroscopy as claimed in claim 1 wherein the reflecting faces are be cut into a substantially cylindrically-shaped crystal.
4. A probe head as claimed in any one of claims 1 to 3 and made of sapphire.
5. Apparatus for use in optical spectroscopy comprising an input fibre for launching by way of a collimating lens radiation towards a chamfered input surface of a probe head having at least five surfaces exposable to a sample under test and a chamfered exit surface positioned to direct said radiation towards a further lens and an output fibre.
6. Apparatus for use in optical spectroscopy including a probe head as claimed in any one of claims 1 to 4.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB919108974A GB9108974D0 (en) | 1991-04-26 | 1991-04-26 | Optical probe heads |
Publications (3)
Publication Number | Publication Date |
---|---|
GB9208843D0 GB9208843D0 (en) | 1992-06-10 |
GB2255200A true GB2255200A (en) | 1992-10-28 |
GB2255200B GB2255200B (en) | 1994-07-13 |
Family
ID=10693969
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB919108974A Pending GB9108974D0 (en) | 1991-04-26 | 1991-04-26 | Optical probe heads |
GB9208843A Expired - Fee Related GB2255200B (en) | 1991-04-26 | 1992-04-23 | Prismatic probe heads for attenuated total reflectance spectroscopy |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB919108974A Pending GB9108974D0 (en) | 1991-04-26 | 1991-04-26 | Optical probe heads |
Country Status (6)
Country | Link |
---|---|
US (1) | US5440126A (en) |
EP (1) | EP0581809B1 (en) |
JP (1) | JPH06506772A (en) |
DE (1) | DE69224635T2 (en) |
GB (2) | GB9108974D0 (en) |
WO (1) | WO1992019956A1 (en) |
Families Citing this family (21)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE4418180C2 (en) * | 1994-06-27 | 1997-05-15 | Emmrich Roland | Probe arrangement for measuring the spectral absorption in liquids, gases or solids |
JP2001337036A (en) * | 2000-05-25 | 2001-12-07 | Masao Karube | Differential spr sensor and measuring method using the same |
GB0021502D0 (en) * | 2000-09-01 | 2000-10-18 | Central Research Lab Ltd | An attenuated total reflectance sensing head |
US7655475B2 (en) * | 2001-01-23 | 2010-02-02 | Fluorocap Limited | Luminescence based sensor using protuberances to redirect light |
JP2002286637A (en) * | 2001-03-27 | 2002-10-03 | Matsushita Electric Ind Co Ltd | Plastic discriminating device |
CA2463151A1 (en) * | 2001-10-11 | 2003-04-17 | Sentelligence, Inc. | Low-cost on-line and in-line spectral sensors based on solid-state source and detector combinations |
US7459713B2 (en) * | 2003-08-14 | 2008-12-02 | Microptix Technologies, Llc | Integrated sensing system approach for handheld spectral measurements having a disposable sample handling apparatus |
US7382458B2 (en) * | 2004-04-01 | 2008-06-03 | Custom Sample Systems, Inc. | Fiber optic fluid probe |
JP5252892B2 (en) * | 2007-11-20 | 2013-07-31 | オリンパス株式会社 | Optical unit |
KR100981215B1 (en) * | 2008-08-07 | 2010-09-10 | 한국오므론전장주식회사 | Rain sensor |
KR100957421B1 (en) | 2008-08-27 | 2010-05-11 | 한국오므론전장주식회사 | Rain sensor |
US8284815B2 (en) * | 2008-10-21 | 2012-10-09 | Cymer, Inc. | Very high power laser chamber optical improvements |
US8488122B2 (en) * | 2010-05-05 | 2013-07-16 | Ysi Incorporated | Turbidity sensors and probes |
US8664938B2 (en) | 2010-05-05 | 2014-03-04 | Ysi Incorporated | Replaceable probe head |
US9170132B2 (en) | 2010-05-05 | 2015-10-27 | Ysi Incorporated | Replaceable probe head having an operational amplifier |
JP5839641B2 (en) * | 2013-10-11 | 2016-01-06 | Dic株式会社 | ATR element, immersion probe, and spectrophotometer |
WO2016077328A1 (en) | 2014-11-10 | 2016-05-19 | In-Situ, Inc. | Compact sensor for measuring turbidity or fluorescence in a fluid sample |
US20160349175A1 (en) * | 2015-05-28 | 2016-12-01 | Microaeth Corporation | Apparatus for receiving an analyte, method for characterizing an analyte, and substrate cartridge |
US10365097B2 (en) | 2015-12-22 | 2019-07-30 | In-Situ, Inc. | Sonde having orientation compensation for improved depth determination |
ITUA20161345A1 (en) * | 2016-03-04 | 2017-09-04 | Eltek Spa | SENSOR DEVICE FOR CONTAINERS OF LIQUID SUBSTANCES |
US10631733B2 (en) | 2017-03-13 | 2020-04-28 | Go!Foton Holdings, Inc. | Lens combination for an optical probe and assembly thereof |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0206433A2 (en) * | 1985-06-25 | 1986-12-30 | The Dow Chemical Company | Methods for measuring the light absorbance of a fluid medium |
Family Cites Families (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1032565A (en) * | 1963-11-20 | 1966-06-08 | Gen Instr Company Ltd | Improvements in and relating to attenuated total reflection spectrometers |
US3393603A (en) * | 1965-04-01 | 1968-07-23 | Philips Corp | Vertical double-pass multiple reflection cell for internal reflection spectroscopy |
GB1264326A (en) * | 1968-06-20 | 1972-02-23 | ||
DE2121744A1 (en) * | 1971-05-03 | 1972-11-09 | Siemens Ag | Optoelectronic device for measuring and controlling the concentration of solutions |
US3669545A (en) * | 1971-05-06 | 1972-06-13 | Wilks Scientific Corp | Apparatus and method for analysis by attenuated total reflection |
US4595833A (en) * | 1983-09-20 | 1986-06-17 | Sting Donald W | Multiple internal reflection cell optical system for use in infrared spectrophotometry of liquid and fluidized samples |
US4602869A (en) * | 1983-12-05 | 1986-07-29 | Harrick Nicolas J | Internal reflection prism liquid cell |
CH665033A5 (en) * | 1985-07-01 | 1988-04-15 | Prutec Ltd | WAVEGUIDE FOR USE AS AN OPTICAL PROBE IN SPECTROSCOPIC ANALYSIS WITH INTERNAL REFLECTION. |
JPS6275230A (en) * | 1985-09-26 | 1987-04-07 | チバ−ガイギ− アクチエンゲゼルシヤフト | Analyzing method |
US4730882A (en) * | 1986-02-10 | 1988-03-15 | Spectra-Tech, Inc. | Multiple internal reflectance spectroscopy system |
CH674082A5 (en) * | 1987-07-10 | 1990-04-30 | Ciba Geigy Ag | Attenuated total reflection cell for spectro-chemical soln. analysis - has collinear entry and exit at opposite ends of bi-prism between liq. and air spaces |
JPH0219745A (en) * | 1988-07-07 | 1990-01-23 | Ricoh Co Ltd | Measuring instrument for physical property value of liquid |
-
1991
- 1991-04-26 GB GB919108974A patent/GB9108974D0/en active Pending
-
1992
- 1992-04-23 DE DE69224635T patent/DE69224635T2/en not_active Expired - Fee Related
- 1992-04-23 EP EP92908850A patent/EP0581809B1/en not_active Expired - Lifetime
- 1992-04-23 WO PCT/GB1992/000744 patent/WO1992019956A1/en active IP Right Grant
- 1992-04-23 GB GB9208843A patent/GB2255200B/en not_active Expired - Fee Related
- 1992-04-23 US US08/140,013 patent/US5440126A/en not_active Expired - Fee Related
- 1992-04-23 JP JP4508059A patent/JPH06506772A/en active Pending
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0206433A2 (en) * | 1985-06-25 | 1986-12-30 | The Dow Chemical Company | Methods for measuring the light absorbance of a fluid medium |
Also Published As
Publication number | Publication date |
---|---|
GB9108974D0 (en) | 1991-06-12 |
DE69224635D1 (en) | 1998-04-09 |
WO1992019956A1 (en) | 1992-11-12 |
EP0581809A1 (en) | 1994-02-09 |
US5440126A (en) | 1995-08-08 |
GB9208843D0 (en) | 1992-06-10 |
EP0581809B1 (en) | 1998-03-04 |
JPH06506772A (en) | 1994-07-28 |
DE69224635T2 (en) | 1999-02-04 |
GB2255200B (en) | 1994-07-13 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20000423 |