Due to rapid development in the field of photonics and optical communicating, assorted measuring techniques are developed utilizing the belongingss of optical maser. Research is besides in advancement to use these tools and techniques in the existent universe commercial scenarios. One of these scenarios is surface raggedness measurings with the aid of non-contact methods. In this respect, our work is concerned with the development of point diffraction interferometer home bases for industrial application of point diffraction interferometry in surface raggedness measuring.
We would wish to show our deep gratitude for Professor Lars Baath for supplying us with this chance and his uninterrupted support and suggestions for the design of PDI home bases. We are besides really thankful to Ms Sameera Atraqji, Ph.D. pupil under our supervisor, for her great support in all aspects.. We are besides grateful to Mr. Bengt Nilsson, MC2 lab, Chalmers University of Technology for turning our design into world by manufacturing these home bases.
The purpose of this Master ‘s Degree thesis undertaking is to plan and develop point diffraction interferometer home bases. In this undertaking the PDI home bases are re-designed, altering the design which was used in old undertakings in Halmstad University. The transparence of PDI home bases can be controlled by surfacing them with NiCr movie. First, four home bases with coating of different thickness of NiCr were developed. The relationship between transmission and the thickness of NiCr was established by proving these home bases for transmission and coefficient of reflection with the aid of a optical maser and an optical power metre.
The soaking up coefficient of clear substrates and contemplation of visible radiation is besides taken into history to accomplish the right consequences. The parametric quantities like the diameter of semi-transparent country around the pinholes and the size of pinholes is chosen after to the full understanding its application. The lay-out and description of design is besides included in the study.
Point Diffraction Interferometer
Nickel Chromium ( Nichrome )
Thickness of metal movie coating
Intensity of Incident visible radiation
Intensity of light go throughing through NiCr
Intensity of light go throughing through glass substrate
Intensity of Transmitted visible radiation
Reflected strength at Air-NiCr interface
Reflected strength at NiCr-Glass interface
Reflected strength at Glass-Air interface
Absorption Coefficient of NiCr
Absorption coefficient of glass
Thickness of NiCr Coating
Thickness of Glass substrate
Ratio between Reflected strength and Incident strength
Transmitted strength + Absorbed strength
Transmittance calculated in first experiment
Transmittance calculated in 2nd experiment
Ratio between focal length and the diameter of entryway student
Foreword _1842612680 ” I
Abbreviations _1842612680 ” three
Contentss _1842612680 ” iv
1 _1842612680 ” Introduction _1842612680 ” 1
2 _1842612680 ” PDI Interferometer System _1842612680 ” 3
3 _1842612680 ” PDI Plates _1842612680 ” 6
4 _1842612680 ” Fabrication Process _1842612680 ” 14
5 _1842612680 ” Experiments with semi-transparent home bases without holes _1842612680 ” 21
6 _1842612680 ” Decision _1842612680 ” 31
7 _1842612680 ” Mentions _1842612680 ” 32
List of Figures
In today ‘s universe where technological promotions are achieved in rapid sequence, there is intensive survey in advancement to develop microscopic mechanical constituents which will cut down the size of normal devices to nanometer graduated table. For this purpose one of the most of import demands is to hold really smooth metallic surfaces which have to be used in these mechanical systems. The raggedness on these surfaces is so little that it is really hard to mensurate it through conventional surface raggedness measuring techniques.
There are two sorts of surface raggedness measuring techniques i.e. contact method and non-contact method. Contact methods are limited in footings of declaration as they have a limited size of the point contact which is touching the surface. There exists contact methods with utmost spacial declaration ( down to atomic declaration ) e.g. scanning investigation microscopy, but these measurings are really clip devouring and non suited for probe of big countries. That is why nowadays most of the research is focused on developing more accurate non-contact methods. One of the most widely used non-contact methods is the optical method.
There are assorted optical methods of which 1 is optical interferometry. A figure of optical interferometry systems are developed and being used for surface raggedness measuring, but most of the systems are either really complex in design or really dearly-won.
Attempts are being made to do optical interferometers simpler in design and much more cost effectual on the other manus bettering the public presentation. One of these simple and cost effectual systems with high public presentation is the point diffraction interferometer.
PDI systems are used in many other optical applications and one of them is Real-time Flow Visualization. Julius E. Okopi has worked in this field under our Supervisor, Professor Lars Baath. Now, this same optical measuring technique is being used for surface raggedness measurings for mechanical technology utilizations. In this respect Sadi Khalid Abu Dalou has done his Maestro ‘s thesis undertaking. His thesis was about 3-D Imaging of Metal surfaces utilizing Point Diffraction Interferometry. There is a PhD undertaking in advancement under our supervisor in which Ms. Sameera Atraqji is working on the development of Hand-held Surface raggedness measuring equipment based on Point diffraction Interferometry.
The PDI system was proposed and developed by R N Smart in 1972 [ 6 ] . The chief constituent of PDI systems is the PDI home base. Previously PDI home bases were developed during Okopi ‘s undertaking in 1992. Now, nevertheless, these home bases are demoing marks of wear and tear and besides the readings are no longer dependable. So our undertaking is to re-design and develop these home bases and acquire these home bases fabricated. The home bases were fabricated at MC2 labs at Chalmers University of Technology.
The aim of this thesis undertaking is to develop and manufacture the PDI home bases for industrial applications. For this intent, we have analyzed the transmission through the PDI home bases, the contemplation of visible radiation and soaking up coefficient of the stuff. Initially, the transmission through simple, semi-transparent home bases was analyzed, which becomes the footing of the thickness of NiCr to be coated during the fiction procedure.
2 PDI Interferometer System
There are many experiments being performed, in different Fieldss, utilizing the point diffraction interferometer system. Here we will discourse the construct and working of point diffraction interferometer in the field of surface raggedness measuring by imaging the surface and analysing the image.
The instrument which measures the fluctuation of stage across a wave-front by interfering with the object beam and mention beam is called an “ interferometer ” . In this undertaking, we are specifically utilizing point diffraction interferometry.
The little distortions in the metal surface can be easy measured by the interferometers. Although many interferometry methods are in usage, one of the most normally used and most precise method is point diffraction interferometry. Common way interferometers are free from environmental restrictions. As they are utilizing a common way design, they are insensitive to the quivers in optical way.
Figure: Light moving ridges through PDI Plate [ 2 ]
The point diffraction interferometer is based on common way interferometry. Both the mention and object beams are transmitted along the same way. An object moving ridge forepart is generated. When any point discontinuity is created in the way of object moving ridge forepart, there will be a alteration in the stage of the object wave-front. Both of these beams will interfere with each other when they pass through the pinhole, harmonizing to the diffraction consequence. They will make a light strength form called an “ interferogram ” , which can be observed and analyzed for farther usage [ 7 ] .
2.2 Setup and working of Point Diffraction Interferometer system
Although different apparatuss have been used in old applications of PDI systems, we are traveling to utilize the same constellation used in the old Thesis of Mr Sadi Khalid Abu Dalou [ 2 ] .
The optical maser beam passes through a beam expander. From the beam expander, the beam passes through beam splitter and one portion of the beam is directed towards the focussing lenses and the other portion is directed towards trial surface. The beam, which strikes the trial surface, reflects back towards the focussing lens and through the PDI home base. This beam is called the “ object beam ” [ 5 ] .
There will be a stage alteration in the moving ridge forepart of the object beam as it strikes on the trial surface. When these beams pass through the PDI home base, the consequence is that they interfere with each other. After the PDI home base, the light beam, which consists of a mention beam and an object beam, creates a light strength intervention form, called an “ interferogram ” , and which is collected on to a recording medium. In our instance, the recording medium is a CCD camera.
Figure: Point Diffraction Interferometer System [ 2 ]
The most of import portion of the PDI system is the PDI home base. It is constructed as follows. The PDI home base is made from a clear substrate, and it is coated with a thin metal movie to do it semi-transparent. The thickness of the metal movie determines the transmission of the semi-transparent country. The last measure is to do a Pinhole in the Centre of the Semi-transparent country which creates a point discontinuity in the way of the incident wave-front. The whole fiction procedure is described in item in subdivision 4 of this study.
3 PDI Home plates
The nucleus constituent of point diffraction interferometer is the PDI home base. The PDI home bases are used to allow the stage beam and mention beam interfere, with the aid of the phenomenon of diffraction of visible radiation. “ When a beam of visible radiation is focused on the pinhole as depicted in figure 3, a little part of light base on ballss through the pinhole to bring forth a spherical wave-front, while the staying part of the incident visible radiation is transmitted through the semi transparent coating. The familial wave-front has the same stage as the incident moving ridge, but its amplitude is attenuated. The grade of fading is determined by the optical denseness of the home base. A Point Diffraction Interferogram which is observed at the image plane, is formed as a consequence of the intervention between the transmitted wave-front and the spherical wave-front. ” [ 1 ]
Figure: Periphery formation utilizing PDI home base [ 1 ]
The transmission of light through point diffraction interferometer plates depends upon assorted parametric quantities e.g. thickness of the NiCr coated on it, the soaking up coefficient of the NiCr, the soaking up coefficient of glass and the contemplation of visible radiation. To plan the point diffraction interferometer home bases, all parametric quantities should be taken into history. In this subdivision, we have taken an overview of all parametric quantities for an efficient design of point diffraction interferometer home bases.
3.2 Parameters for design of PDI home bases.
For an efficient design of a point diffraction interferometer, the parametric quantities like thickness of the metal movie coated on it, the soaking up coefficient of stuff, contemplation of visible radiation from the surface of point diffraction interferometer home bases and the diameter of the pin-hole and the country of the semi-transparent round part around the pinhole are discussed.
3.2.1 Transmittance through PDI home bases
As discussed earlier the transmission of point diffraction interferometer plates depends upon the thickness of the metal movie deposited on it and the soaking up coefficient of the stuff. We can utilize the undermentioned look,
x= Thickness of metal movie coating
Here in our undertaking, we used Nickel Chromium ( NiCr ) as surfacing stuff. Other stuffs like Gold ( Au ) may besides be used.
3.2.2 Thickness of metal movie coating
The thickness of the metal movie coated on to the clear substrate is an of import parametric quantity for finding the transmission through the point diffraction interferometer. A bed of metal, like NiCr, is deposited on the clear substrate which is used to command the transmission. The greater the thickness of the metal movie on the clear substrate, less will be the transmission of visible radiation. Initially, simple semitransparent home bases with the thickness 7.5nm, 34nm, 42nm and 60 nanometer for point diffraction interferometer were made merely for proving intents.
3.2.3 Absorption coefficient of stuff
When the light base on ballss through the material some of the visible radiation is absorbed. It is the features of the stuff which determines the extent to which visible radiation can perforate through any stuff. When the light base on ballss through any crystalline stuff, due to its interaction with atoms and molecules, some of it is lost. To gauge the transmission it is necessary to see the soaking up coefficient of stuff besides. In our undertaking we have measured the soaking up coefficient of the stuff by experimenting with the trial plates ( translucent home bases ) . The experimental set-up and measurings will be discussed in ulterior subdivisions.
The home bases with merely the semi-transparent coating were tested and the measurings were taken and the computations were done to gauge soaking up coefficient.
3.2.4 Area of semi transparent round part
Around the pin-hole, the metal movie is coated harmonizing to the coveted thickness. The translucent part becomes opaque by lodging the metal movie on it. When the light base on ballss through it, it produces the object wave-front. The country of translucent round part should be designed to be five times more than the topographic point size of the optical maser beam used. In our undertaking we suggested this translucent country to be 300Aµm in diameter.
3.2.5 Size of pin-hole
The fiction procedure of the point diffraction interferometer is finished when a round pin-hole is etched in the center of the translucent country. The size of the pin-hole depends upon the transmission through the coating of metal movie around it. A mathematical manner to make up one’s mind it is that it should be half the diameter of the Airy disc of the focussing lens. The Airy disc diameter of the lens is a map of F-number ( f # ) of the lens and wavelength ( I» ) of visible radiation used. It can be calculated as ;
Airy diameter = 2.44 A- f # A- I»
In our undertaking we suggested the size of pin-holes as 2.5Aµm, 3.5Aµm, 4.5Aµm and one without holes.
3.3 Description of proposed Design of PDI home bases
In this subdivision, inside informations are given of our proposed design. The specifications of the design are besides discussed in this subdivision.
3.3.1 Lay-out of PDI home bases
The base stuff used for the PDI home bases is Soda-Lime mask-blank. For this intent, we have used the 3in * 3in ( 75mm * 75mm ) Soda lime glass home base with 100nm Chromium ( Cr ) coating. It is divided into four equal quarters of equal dimensions and an equal figure of PDI units on each one-fourth. Each one-fourth has nine PDI devices i.e. nine round, semi-transparent countries with a pinhole in its centre. The size of all the pinholes in a individual one-fourth is the same and the size of all the semi-transparent countries in all four quarters is same i.e. 300I?m. In three quarters there are pinholes with sizes 2.5I?m, 3.5I?m and 4.5I?m severally, and in the 4th one-fourth there are no pinholes in the centre of the translucent country. This is done in order to hold a control subdivision for proving the transparence of the home base. A unsmooth design layout is shown in figure 4.
Figure: PDI plate design layout
3.3.2 The alliance of pin-holes
Here, we have proposed a design with point diffraction interferometer home bases in four quarters where each one-fourth has an equal figure of PDI units. There are three rows, and each row contains three point diffraction interferometers PDI units. All these units are equidistant from next PDI unit. The diameters of holes suggested were 2.5Aµm, 3.5Aµm, 4.5Aµm and one one-fourth with no holes. The 4th one-fourth in which we have merely semi-transparent countries are besides aligned in the same mode as the other three quarters.
3.3.3 Size of Semitransparent country
The translucent country is created by surfacing the metal. “ A good regulation of pollex to utilize in taking the semi-transparent part is to guarantee that the country is big plenty to do it seeable to the bare oculus and it should be a factor of 5 larger than the topographic point size of the optical maser used for the experiment. “ [ 1 ]
Figure: Size of semi-transparent country
3.3.4 Space between the centres of round translucent country
In our undertaking we suggested the infinite between centres of translucent countries is 5mm.This agencies that each semi-transparent country is 5mm apart from next PDI units as shown in figure 6. This spacing is done in order to turn up the PDI unit easy on the PDI home base. In the old design the procedure of turn uping the pinhole was really hard as it has to be located with the bare oculus by go throughing the optical maser through it. Now in our design it will be easier to turn up the pinhole by merely mounting the home base in the rail system through which we can accurately travel the home base in millimetres.
Figure: Spacing between the next PDI units
3.3.5 The arrangement of Markss
In our design, we placed the Markss ( + ) for alliance. It will go easy to find the exact centre after fiction, when the home base will be divided into four quarters of equal dimensions. These Markss will besides be utile for citing by the lithography machine for etching the pinholes right in the Centre of the semi-transparent countries. These Markss are shown in figure 7
Figure: E-beam Markss
4 Fabrication Procedure
The point diffraction interferometers home bases were manufactured at the nanoscience lab MC2, Chalmers University of Technology. A basic fiction procedure was used for the development of point diffraction interferometer home bases. In this subdivision, we will supply an overview of the fiction procedure.
4.1 Fabrication procedure of Semi-transparent home bases
We tested the four point diffraction interferometer home bases of different thicknesses of NiCr e.g.7.5nm, 34nm, 42nm and 60nm. First these home bases were fabricated in Chalmers University of Technology labs and forwarded to us for proving of their transmission. The testing was done in Halmstad University lab under the supervising of our supervisor, Professor Lars Baath. The inside informations of the experimental apparatus, measurings and computations on the footing of these measurings are described in the following subdivisions.
4.1.1 Coating of translucent stuff
The fiction of semitransparent home bases was done by metal coating on the clear substrate e.g. glass. Thicknesss of 34nm, 42nm, 60nm and 7.5nm of NiCr were deposited on the clear substrate. The intent of these assorted thicknesses is to gauge the proper thickness, with the aid of experiments, to be coated for the needed 2 % and 4 % transmission.
During the fiction procedure foremost of all, all the home bases were cleaned by ozone ( O3 ) , an allotropic signifier of O, for 20 proceedingss. After that, one of the home bases was mounted in the thermic vaporization system. 42 nm thickness of metal movie ( NiCr ) was deposited. After taking it from the thermic vaporization system, the same procedure was repeated for the staying three home bases e.g.7.5nm, 34nm and 60nm.
4.2 Fabrication procedure of PDI home bases
In this subdivision, the complete fiction procedure of PDI home bases is discussed. A four inch mask was foremost prepared with E-beam lithography. This mask merely contains empty infinites for Semi crystalline countries with 300I?m of Cr etched from the Cr coated Soda-Lime Mask-Blank. This home base was used as a stencil for the fiction of the original home bases. Four 3inch home bases were fabricated utilizing the four inch mask and photolithography. The intent of doing this 4 inch mask is to hold a stencil which can be used to do three inch home bases in big Numberss. Then, these three inch home bases are coated with NiCr harmonizing to the given specifications i.e. 40nm and 50nm. Finally, the pin hole is etched in the Centre of each semi-transparent country. This whole procedure is wholly described in the figures as follows.
4.2.1 Pattern readying
The first measure was to plan the layout in AutoCAD. There were some limitations for wholly interpreting our design into practical AutoCAD design which have to be used for the fiction. One of them was the form of pinhole, which in our design was round, had to be replaced by an octangular form. This was done, as the e-beam lithography machine is non able to compose the round form of this size ( 2.5I?m and etc. ) with utmost preciseness. So the closest form to a round form is an octagon and so it was replaced. Two beds were used as one bed for restricting apertures, light alliance and e-beam alliance by utilizing a photolithography mask home base and the 2nd bed for making the pinholes by utilizing the e-beam lithography. The basic design is shown in figure 9.
Figure: Pattern Preparation
Now our design in AutoCAD format was exported into the DXF ( Autodesk pulling exchange ) format, version R12-R14 and so it was converted to GDS form format. In e-beam lithography, a major trouble is declaration ; it may be limited by the sprinkling of negatrons. When negatrons hit the surface of resist they penetrate the implicit in substrate and a hit occurs. This causes to lose the energy of negatrons or they leave the stuff. This is called “ backscattering ” . Due to backscattering, negatrons can enlighten from the Centre of the exposure beam of the optical maser. This besides affects the adjacent irradiations ‘ . This phenomenon is known as the “ propinquity consequence ” [ 3 ] . To cut down the propinquity consequence in the fiction procedure, the pinhole bed was locked to a 50nm grid. Last, the GDS file was converted into JEOL51 e-beam ( machine readable ) format for JEOL equipment.
4.2.2 Preparation for PDI aperture exposure mask
For commercial intents, a 4-inch mask was developed before which was used as stencil or dye for fiction of home bases. A four inch sodium carbonate calcium hydroxide mask space was prepared with 100 nm Cr coating. The UV5 negatron beam resist was spin coated at 3000 r.p.m ensuing in a thicknesss of 0.8Aµm. The substrate was soft baked at 130C for 3 proceedingss on a hot plate. The ground for soft baking is to extinguish the dissolver in the resist.
Figure: 4-inch Photomask readying
Next, the file prepared for form in JEOL51 format was exposed in a JBX5DII negatron beam lithography system, holding the specifications 50KVA, 10nA, 300Aµm aperture, 0.25Aµm beam stairss and 12Aµc/cm2 exposure dosage. A station exposure bake was given to substrate at 130C for 12 proceedingss in the oven. After baking the substrate, MFA developer was used to develop for 60 seconds. The home bases were so rinsed in H2O. The home bases were baked in oven at 130C for 25 proceedingss to better the resist adhesion. Oxygen plasma was used to clean the surface. Subsequently the home base was dipped in H2O and etched for 65seconds in standard mask Cr-etch. The resist was striped by utilizing remover 1165 ( N-Methyl-Pyrrolidone ) overnight. The whole procedure is described in graphical manner in figure 10.
4.2.3 PDI aperture exposure lithography
A 3 inch sodium carbonate calcium hydroxide mask space is used with 100 nanometers of Cr coating. By spin surfacing S-1813 exposure resist is coated at 3000 revolutions per minute. A 1.5Aµm thick bed of exposure resist is deposited on the home base. The substrate was allowed to soft bake at 130C for 3 proceedingss on the hot plate.
Figure: PDI Aperture Photo Lithography
The PDI aperture form is exposed onto the 3-inch home base in Karl Suss MA6 mask aligner, utilizing the 4-inch exposure mask from the old measure. This substrate is so developed for 45 seconds in MF319 developer solution. After developing the resist the substrate is rinsed in H2O and so etched for 75 seconds in standard Cr etch. Then the resist is removed with the Remover 1165 and rinsed with H2O. The graphical account is given in figure 11.
4.2.4 Semi-transparent bed deposition
For this measure, the home bases prepared in the old measure with merely 300I?m of Cr etched are coated with NiCr surfacing. The thicknesses specified in our design are 50nm and 40nm for 2 % and 4 % severally. So two out of four home bases are coated with 40nm NiCr and two of them are coated with 50nm.
Figure: NiCr coating in Thermal vaporization system
First the home bases from the old measure are cleaned in ozone for 20 proceedingss. Then the home base is mounted in the thermic vaporization system and 40nm or 50nm NiCr is deposited as shown in figure 12. The thickness of the NiCr surfacing depends on vaporization clip. The home base is so removed from the system and the procedure is repeated for other home bases.
4.2.5 PDI pin-hole E-beam lithography
To make the pinholes in the translucent part e-beam lithography is used. UV5 negatron beam resist was spin coated at 3000 r.p.m ensuing in a thickness of 0.8Aµm. These substrates were baked at 130C for 3 proceedingss. Now propinquity corrected “ PDI pin-hole bed “ was exposed in the JBX5DII negatron beam lithography system at 50KV, 0.25nA, 300Aµm aperture 0.05Aµm beam measure, 12Aµc/ exposure dosage. Mark sensing is used to aline the pinholes right in the centre of the apertures as shown in figure 12.
A station exposure baking of the substrate at 130C for 12 proceedingss was carried out. This station baked substrate was developed for 55 seconds in MF24A developer and was so rinsed with H2O. This substrate is allowed to bake at 130C for 25 proceedingss in the oven to better the resist adhesions. Oxygen plasma is used to clean the surface. Then once more it is rinsed with H2O. It is now dipped in Cr-etch for 25 seconds for etching off the NiCr. Then the resist was stripped in remover 1165 ( N-Methyl-pyrrolidone ) for one hr. After being taking out from remover it was once more rinsed with H2O. Graphic representation of the procedure is given in figure 12.
Figure: Pinholes fabricated by e-beam lithography
4.2.6 Cutting of the home bases
Finally, when the fiction procedure was completed the home base was mounted onto a tape-ring and so placed in the Disco DAD3350 diamond proverb. The 3 inch home base was divided into separate devices as shown in Figure 13.
Figure: Film editing of the home bases
5 Experiments with semi-transparent home bases without holes
5.1 Testing for the relationship between transmission and thickness of NiCr.
In this portion, we have studied the relationship between transmission through point diffraction interferometer and above specified thicknesses to gauge the soaking up coefficient of NiCr. This will be used in gauging the needed thickness of NiCr to be deposited to acquire 2 % and 4 % transmission.
5.1.1 Experimental apparatus
In our experiment, we passed the Helium Neon ( HeNe ) optical maser through the power regulator and so through the NiCr coated trial home bases. The familial strength of visible radiation is measured by Thorlabs optical power metre. By linking the detector to the strength metre, we observed different strengths of optical maser for different PDI home bases at the strength metre. We took two sets of measurings by puting the initial strength of the optical maser through the power regulator.
5.1.2 Equations for soaking up coefficient of NiCr.
Here, we calculate the soaking up coefficient of NiCr by taking two sets of readings. We have taken into consideration all the reflected strengths, transmitted strengths and power losingss due to absorption coefficient of NiCr and Glass. The computation of soaking up coefficient ( ) and transmission is done as follows.
Figure: Factors lending to the transmission of light through semi-transparent home base
From Figure 14, we can decently understand the whole procedure through which the visible radiation transmits through a semi-transparent home base. When incident visible radiation ( I0 ) strikes the NiCr surface, a portion of it is reflected back which is denoted as IR1 and portion of it is transmitted through NiCr with some losingss due to its soaking up coefficient I±1. It is denoted as I1, and it is given as ;
When this IA1 work stoppages on the interface of NiCr and glaze some of it is reflected back i.e. IR2. The portion of it transmitted through the NiCr substrate, with some losingss due to absorption coefficient I±1, is known as “ I2 ” . It is given as
When this I2 comes out of glass and enters air, portion of it is reflected back, denoted as IR3 ; the other portion is absorbed in the glass ( I±2 ) transmitted out as Ix, which is given as,
We approximated the soaking up coefficient of glass ( I±2 ) to zero as ideally there is no soaking up loss in glass.
All the invariables in the above equation are taken as a individual invariable, B, given as,
The measurings are taken by utilizing the apparatus described in subdivision 5.1.1. There is a power regulator in forepart of HeNe gas optical maser which is used to command the power of optical maser visible radiation, which strikes the semi-transparent home base. The following two tabular arraies are prepared by mensurating the end product optical maser strength which is passed through the semi-transparent home base. In first set of measurings the initial strength ( I0 ) is taken as 1002I?W and in the 2nd set, the initial strength is taken as 2003I?W.
Thickness of NiCr,
Power ( without Plate ) , I0, I?W
Power ( With Plate ) ,
( ratio )
Thickness of NiCr,
Power ( without Plate ) , I0, I?W
Power ( With Plate ) ,
( ratio )
The undermentioned two graphs are obtained by plotting the values of thickness against the transmissions from the tabular arraies above. These graphs are foremost plotted and so fitted to the exponential look:
As it is shown that the above two graphs have really similar values, to acquire a mean or mean value of both graphs, both sets of measurings have to be plotted in the same graph. To obtain a combined graph, the old two sets of measurings are combined in the undermentioned tabular array.
Thickness of NiCr,
Power ( without Plate ) , I0, I?W
Power ( With Plate ) ,
( ratio )
This graph is obtained by unifying the values of table 1 and table 2 to acquire an mean value of the exponential tantrum.
When the values in the merged graph are fitted exponentially, we get an exponential equation depicting the form in the values. This equations is as follows
y = 0.6237e-0.068x
By comparing it with the equation
We can acquire I±= 0.068 Garand rifle
By utilizing these values of B and I± , we can gauge the thickness of NiCr to be coated for 2 % and 4 % transmission.
For 2 % :
By seting the values of I± and B in the above equation, we will acquire the value of thickness of NiCr as
For 4 % :
By seting the values of I± and B in above equation, we will acquire the value of thickness of NiCr as
These are the needed thicknesses of the semitransparent plates to be prepared.
5.2 Testing for relationship between coefficient of reflection and thickness of NiCr.
In this subdivision, we are traveling to set up a relationship between thickness of NiCr and the contemplation of visible radiation through translucent point diffraction interferometer home bases. An experimental apparatus is described below to happen the relationship.
5.2.1 Experimental apparatus
To happen the contemplation we passed the visible radiation through a power regulator.The visible radiation passed from the regulator and was allowed to hit the surface of the PDI home base. After contemplation, the beam of visible radiation goes to Thorlabs light strength detector. By utilizing the strength metre we observe the different reflected strengths of visible radiation for different home bases. Three sets of readings were obtained in this exercising.
The measurings are taken by utilizing the apparatus described above. There is a power regulator in forepart of the HeNe Gas optical maser which is used to command the power of optical maser visible radiation which strikes the semi-transparent home base. The undermentioned three tabular arraies are prepared by taking the measuring of end product optical maser strength which is reflected against the semi-transparent home base. In first set of measurings the initial strength ( I0 ) is set at 2mW and in the 2nd set the initial strength is taken as 1.454mW and, in the 3rd set of measurings, the initial strength is 1.567mW.
The measurings are shown in tabular signifier in the undermentioned tabular arraies.
Thickness of Plate
( nanometer )
Initial Intensity, I0
( mW )
Reflected Intensity, IR
( mW )
Thickness of Plate
( nanometer )
Initial Intensity, I0
( mW )
Reflected Intensity, IR
( mW )
Thickness of Plate
( nanometer )
Initial Intensity, I0
( mW )
Reflected Intensity, IR
( mW )
5.2.3 Calculations for contemplation of visible radiation from tabular arraies
To cipher the contemplation of light, we used the tabular arraies above. From all the three tabular arraies the values of the ratio between initial and reflected strengths for the mirror and 7.5nm home base are non considered as the mirror has about 100 % coefficient of reflection, and the transmission for 7.5nm home base is really high.
We know that
We can cipher the value of “ R ” by taking the average values of 34nm, 42nm and 60nm severally. So by taking the mean values from three mentioned tabular arraies we have,
n=9 and X=0.385, 0.414, 0.393, 0.406, 0.4368, 0.4133, 0.3795, 0.4095, 0.388
The average value of the above informations therefore becomes:
This is the needed value of “ R ” .
The value of “ C ” can be calculated by utilizing above look we derived,
Similarly, we can cipher the Standard divergence by utilizing the undermentioned expression ;
SD ( I? ) =0.0181
5.3 Consequences and treatment
From the measurings in the last two experiments, it becomes clear that the transmission of visible radiation is diminishing as the thickness of NiCr is increasing.
From our computations in first experiment, we got the value for changeless ( B ) of 0.6237 and a value of Absorption coefficient ( I± ) of 0.068m-1. From these values, we can propose that, for 2 % and 4 % transmission, the thickness of NiCr should be 50.587nm and 40.394nm. From the computations in the 2nd experiment, we got the value of C as 0.59271.
If we look at the look of transmission from first experiment, which is:
To happen the ideal transmittal we can presume soaking up coefficient for NiCr peers zero, which gives us the ideal transmittal from the first experiment as follows
From 2nd experiment we have,
Let us presume, for ideal transmittal, loss due to soaking up ( A ) is zero so,
If we compare transmittal from the first experiment ( T1 ) and transmission from the 2nd experiment ( T2 ) , we can comfortably state that both are about equal within the mistake scope which is calculated as A±0.0181 ( standard divergence ) . This consequence shows the consistence of our informations.
We have forwarded our demands to the MC2 lab for the fiction of the PDI plates harmonizing to our design and specifications.
Our chief end, to plan and develop new PDI home bases for the bing PDI system, is achieved, as it was antecedently discussed that the old PDI home base is broken and unable to give us accurate readings.
The complete designing and developing procedure was discussed in item. The first measure was to prove the semi-transparent home bases for obtaining the relationship between the transmission of visible radiation and the thickness of the NiCr coating. In this measure, we have foremost measured the transmission of visible radiation through trial home bases with the thicknesses 7.5nm, 34nm, 42nm and 60nm. These measurings were used to cipher the soaking up coefficient I± of NiCr, which was found to be 0.068m-1, and the value of the invariable B which amounts to 0.6237. In the 2nd experiment, the value of the changeless, C, was calculated from coefficient of reflection measurings on the trial plates. The value came out to be 0.5927.
In the 2nd measure, the design was made harmonizing to the consequences deduced in the first measure. There were some basic alterations in the physical design from the old home base made in 1992. These alterations assure better public presentation and more accurate readings. It besides assures easier handling and experiment apparatus. Our design has besides ensured easier commercial production of the PDI home bases in the hereafter, as the basic 4-inch mask is present with the proper design specification in the graphical format.
These home bases will be used in the undertaking for mensurating surface raggedness for mechanical technology applications in the close hereafter.