US 3542482 A
Description (OCR text may contain errors)
United States Patent Inventor Paul A. Wilks, Jr.
Darien, Connecticut Appl. No. 681,472
Filed Nov. 8, I967 Patented Nov. 24,1970
Assignee Wilks Scientific Corporation South Norwalk, Connecticut a corporation of Connecticut VARIABLE ANGLE INTERNAL REFLECTION ATTACHMENT 2 Claims, 10 Drawing Figs.
 References Cited UNITED STATES PATENTS 3,157,788 11/1964 Roche 356/244 3,332,315 7/1967 Wilks,.lr 356/244 3,240,111 3/1966 Sherman et all.
Primary Examiner- Ronald L. Wibert Assistant Examiner-V. P. McGraw Att0rney-Smythe & Moore US. Cl.. 356/244 Int. Cl ..G01n 21/16; GOlj 3/00 Field ofSearch 356/244, 74; ATR/Digest 1. VARIABLE ANGLE INTERNAL REFLECTION ATTACHMENT SPECIFICATION The present invention relates to internal reflection spectroscopy and more particularly to an attachment for varying the angle of incidence of a beam of radiation entering a sample wherein the beam is reflected within the sample a multhose wave lengths where the material absorbs energy. This attenuated radiation, when measured and plotted as a function of wave length by a spectrophotometer. will give an absorption spectrum characteristic of the material.
The depth to which the radiation penetrates is a function of: (l) The wave length oflight, (2) The refractiveindex-of both of incidence. Thcinternal reflection means is mounted on a member which is linearly movable on the platform by rotation of an adjusting knob. Themovable member and the reflecting surfaces are linked in pantographlike fashion by a scissorsjack assembly. By rotating the single adjusting knob, the reflecting surfaces are moved in synchronism with the internal reflection means mounted on the movable member so that the beam of the reflector and sample, and (3) The angleof incident radiation. If the depth of penetration versus angle of incidence is plotted in a region where there is maximum absorption by the sample. the penetration will increase most rapidly when the angle of incidence at the interface between the sample and prism is very near thecritical angle but it is relativelyslight at angles well removed from the critical angle.
Nearly all the energy goes into the sample when the critical angle is exceeded.
A typical'plot of the index of refraction of a material versus wave length in the vicinity of an absorption band willshow that the index of refraction undergoes radical variation in this region. There will be a point at which the index of the sample is greater than that of the reflector. At this'wave length, there is no angle of incidence at which internal reflection can take place and nearly allthe energy will pass into the sample. The recorded internal reflection absorption band will, thus, be very strong but broadened toward long wave length and, hence, greatly distorted as compared to that measured by transmission.
It will be apparent that in order to obtain internal reflection spectra that are nearly identical to transmissionspectra a rela radiation is held in focus on the entrance face of the plate at each angle of incidence.
Other objects, advantages and features of the present invention will become apparent upon'reference to the accompanying description and drawings, which are merely exemplary.
In the drawings: 1
,FIG. I.is a top plan view of the variable angle internal reflection attachment of the present invention;
FIG. 2 is a front elevational view ofthe apparatus of FIG. I;
FIG. 3 is a bottom plan view of the apparatus shown in FIG. I with the enclosure removed to illustrate the connecting linkage;
FIG. 4 is an elevational view of thc'apparatus illustrated in FIG. 3;
FIG. 5 is a top plan view ofthe apparatus of FIG. I but with the reflecting surfaces removed to illustrate the mounting means therefor;
FIG. 6 is a sectional view taken along the line 6.6 ofFlG. 3;
FIG. 7 is a sectional view taken along the line 7-7 of FIG. 3;
FIG. Sis a plan view ofa portion of the linkage illustrated in FIG. 3 with the links having the reflecting surfaces mounted thereon being shown in shaded lines and the remaining components ofthe linkagesystem shown in dash lines;
FIG. 9 is'a view similar to that of FIG. 8 but showing schematically the linkage system and the movement of the reflecting surface; and
FIG. 10 is a schematic view illustrating how movement of the reflecting surfaces varies the angle of incidence of a beam of radiation to the entrance of a sample for multiple internal tively high' index reflector should be used. Also, an overall Itis possible, however. to multiply the amount ofabsorption by multiplying the number of reflections. This is analogous to increasing the path length in transmission cells. The multiple reflection approach can thus produce undistorted spectra of any desired intensity provided there are enough reflections.
One of the objects of the present invention is to provide an improved apparatus for varying the angle of incident radiation with a multiple internal reflector plate.
Another of the objects of the present invention is to provide an apparatus for varying the angle of incident radiation onto a multiple internal reflection plate while holding the beam of radiation in focus at the entrance to the plate.
In one aspect ofthe invention there maybe provided a varition means. A plurality of reflecting surfacesare movably mounted. on the platform to reflect a beam of radiation into and out of the internal reflection means. Means operatively connect the internal reflection mean and the plurality of reflecting surfaces for holding a beam of radiation in focus on the entrance of the internal reflection mean at varying angles reflection therein.
Proceeding next to the drawings IYlIdI'tilI'! like reference symbols indicate the same parts throughout the -arious views a specific embodiment of the present invention will be described in detail.
As may be seen in FIGS. 1 and'2, the attachment according to the present invention is indicated generally at 10 and comprises a base 11 which is in the form of a casing or enclosure with an upper surface or platform 12.
A sample platform 13 ismovably mounted between fixed guides 14 and 15 secured to top face 12 with guide 14 having an index lothereon which registers with ascale of angles 17 on the sample platform. The angles of the scale 17 represent angles of incidence of a beam of radiation to a sample carried in a fixed plate sample holder (not shown in the drawings) but which ismounted on the movable sample platform 13.
Also'mounted on the top face 12 are reflecting surfaces I8,
19, 20 and 2I. Each of the reflecting surfaces are secured in adjusting knob 23 on the top thereof to adjust by rotation the reflecting surfaces.
Referring next to FIGS. 3 and 4, the adjusting mechanism for moving the reflecting surfaces in conjunction with the sample platform comprises a block 24 mounted on the underside of the sample platform and having, a threaded bore therethrough. A threaded shaft 25 is journaled at 26 and 27 within space 11 andis threadedly engaged with the threaded bore of block 24. The outer end of the shaft indicated at 28 maybe provided with an adjusting knob29 illustrated in FIGS.
. land 2.
' able angle multiple internal reflection apparatushaving a platform upon which there is movably mounted an internal reflec- The linkage system actually comprises two mirror opposite pantograph linkage arrangements which may be seen'in FIG. 3. The linkage comprises afirst link 30 which has one end pivotally mounted at 31 and a slot 32 in its other end. Pivot mount 31 is'a pin which projects above the top surface 12 and the reflectingsurfaces 18 and 21 are mounted thereon.
A second link 33 is provided which has a slot 34 in its inner end and a pivot pin 35 at its other end.
A connecting'link 36 is connected between the pivot point 31 and pivot pin 35. y
Pin 35 of second link 33 extends upwardly beyond the top surface through arcuate slot 37 and reflecting surfaces 19 and 20 are attached to these pins.
Links 38 and 39 are pivotally connected at 40 to the movable sample platform and link 38. is pivotally connected to pin 35. Link 39 is connected to pin 41 which is guided in slot 34 of link 33. There is-a link 42 connected between pin 41 and a pin 43 mounted on connecting links 36.
A link 44 is pivotally connected between pin 43 and a pin 45 which is guided in slot 32. There is a remaining link 46 pivotally connected between afixed pivot pin 47 and the pin 45.
As can be seen in H6. 6, movable sample platform 13 may be provided with vertical pins 48 upon which the sample holder is mounted. The platform is guided on the undersurface of the top surface 12 by antifriction ballbearings 49. Links 38 and 39 are separated by an antifriction surface 50 which may be ofa plastic such as teflon or the like. A further bearing 51 is provided surrounding pin 40 and mounted on the underside of the movable sample platform 13. A somewhat similar arrangement of antifriction bearings maybe used for the remaining pivotal and slot connections of the linkage assembly. Another such pivotal connection may be seen in FIG. 7. it can be seen that the link 33 is secured to the pin 35 by means of set screw 52.
'The movement of the various links which results in repositioning of the reflecting surfaces may be seen in FIGS. 8 and 9.
In FIG. 10, a beam of radiation is'indicated at 53 and is reflected from reflecting surface 18 onto reflecting surface 19 and then to entrance face 54 of a' sample 55 held between reflecting surfaces 56 and 57. 'The beam is multireflected within the sample as indicated schematically.
Movement of the reflecting surfaces 18 and 19 and of the sample platform 13 to vary the angle .of incidence will cause the beam of radiation to follow the path of the dash lines indicated at 58. It will be seen that the angle of incidence of beam 58 with entrance face 54 of the sample will be varied from that of beam 53.
It will be apparent that during the synchronousmovement of the reflecting surfaces and the sample platform, the distances between reflecting surfaces 18 and 19 and 21 and 20 will remain constant. Accordingly, the image of the radiation beam will be constantly focused on the entrance face of the sample. Further requirements of the optical system compris ing the reflecting surfaces and the sample are that the pcrpen dicular to reflecting surface 18 must bisect the angle between reflected from said first re the incoming beam and the reflecting beam going to reflecting surface 19. The perpendicular to reflecting surface 20 must bisect the angle from exit face of the sample to reflecting surface 20 and to reflecting surface 21. The perpendicular to reflecting surface 21 must bisect the angle formed by reflecting surfaces 21, 20 and the entrance slit of the spectrometer. The spectrometer may be positioned behind a plate 59 mounted on base 11 as shown in FIG. 1.
Thus it can be seen that the present invention provides an attachment for, making multiple intern-a1 reflection measurements at a continuously varying angle of incidence. The reflecting surfaces are interconnected by a linkage arrangement which. together with the sample platform, is moved to maintain the proper relationship between the reflecting surfaces and the sample platform.
It is to be understood that various details of construction and arrangement of parts may be'made'without departing from the spirit of the invention except as defined in the ap pended claims.
' 1. ln a variable' angle multiple internal reflection apparatus. the combination including a platform. a movable multiple internal reflection plate holding means, a first reflecting surface means adjustably mounted on said platform for receiving a beam of radiation. a second reflecting surface means-adjustably mounted on said latform for receivin the beam ecting surface and redlecting the beam to the entrance face of a multiple internal reflection plate means on said holding means, a third reflecting surface means adjustably mounted on said platform for receiving said beam from the exit face of said multiple internal reflection plate. a fourth reflecting surface means adjustably mounted on said platform for receiving the beam reflected from said third reflecting surface means and reflecting the beam outwardly of said apparatus, and linkage means connecting said mi ltiple reflection plate holding means and said four reflecting surface means, said linkage means being arranged to hold the distance constant between said first and second reflecting means and the distance constant between said third and fourth reflecting means and to hold said beam in focus relative to the entrance and exit faces of said multiple'internai plate means as the angle of incidence is changed by moving said mot able internal reflection plate meansand the angular relation of said reflect ing means to said internal reflection plate means.
2. An apparatus as claimed in claim 1 wherein the second and third reflecting surface means are mounted on pivot means which are also arcuatcly movable.