Optics 1

OPTICS As I understand, purpose of our meeting here is to work out a frame- work of a syllabus which can provide a comprehensive education which provides for both the core study of a subject as also selective study of more restricted topics of the subject through elective courses. Optics is a subject which has been neglected in graduation and to the best of my knowledge non-existent at M.Sc.

This is in-spite of the fact that the subject has one of the widest base in modern technology! Let me make it clear right in the beginning that I have almost no experience in teaching either at graduate or at post-grad. level, and none in syllabus framing. Most of you here are much better qualified in that respect. So, I will just give a broad picture of scope of optics as in optical engineering and pure science.

Although the physical nature of light is described as a wave, so far as the its applications go by far most of them are covered under ‘ray optics’, which we call ‘Geometrical Optics’. This must be kept in mind when we consider framing early stage elective course. A more advanced course in geometrical optics would be dealing with properties of lens combinations like various types of eye- pieces, camera lenses, vignetting, etc.; various prism devices.

Then there is a large field in biophysics that needs optics, the physiology of ‘vision’ As an interesting side line, I may mention one of the strong objection to Darwin’s theory of evolution raised by proponents ‘ intelligent design’ was “how could have such an intricate mechanism like an eye have evolved only through selection and mutations?” One large area of application of optics is in the field of ‘colours and dyes’ and

which needs understanding the light scattering and absorption by pigment particles. Except for the ‘scattering and absorption’, all these applications that I narrated are concerned with only the ‘Ray Optics’ Let us now turn to specific wave aspects. The concepts of image formation and image resolution have undergone a vast change in modern optics, which I doubt whether it finds place in our current

teaching of optics. The Fourier optics and the treatment of image formation on the basis of the Fourier components takes now the center stage. I will give an example of why one needs a more sophisticated treatment of image resolution. Our usual criterion for image resolution considers resolution of a ‘point’ objecct. Now let us consider detecting a faint point source located close to a bright point source. One now needs to ‘modify’ the classical Airy diffraction. This is what

“ Apodization” achieves- literally meaning ‘ removing the feet!” Applications to astro- nomy are,1) detecting a faint star close to a very bright star, detecting an extra-solar planet. Apodization is achieved by suitably modifying transmission of light across the telescope aperture, there by suitably modifying the appropriate Fourier components of the image. Let us now consider the most challenging application of the Fourier imaging-forming a milli-arc sec image of an astronomical

object by interferomerically combining light from separate telescopes. { Image resolution D/ λ is actually Base line/ λ }. Interestingly, in spite of much larger value of wavelength of radio waves very high resolution by interferometric methods was first achieved in radio, this was because radio waves are detected primarily as ‘wave amplitude’, in optics one normally detects |Amp| 2 . In the optical region it has been achieved only very recently.

I jumped from the industrial optics straight the most advanced topics in modern optics! Let me come back to some ‘not so advanced’ topics. Let us consider polarization of light. Polarization has application in analyzing stress distribution in a structure, which is well known. It also is a powerful tool in minerology- a topic known as optical minerology. This leads to the propagation of light in anisotropic media-which you teach as propagation in uniaxial and biaxial

Crystals. Related topic is the ‘chirality’- propagation in certain structures with phase velocities for the right and left circularly polarized light.{ As a digression it is amazing that the life on the earth has amino acids and sugars with specific chirality: all sugars in living systems are right handed, all amino acids are left handed. On the other hand, in space one finds all these molecules with equal probability for both right and left handed varieties. A deep mystery!}

Optical anisotropy can also be induced by applying a magnetic field. The associated electro- and magneto-optical effects have been very useful in designing fast light modulators. Related topic is of liquid crystal displays. How to describe propagation of polarized light and how to quantify light beam in terms of its polarization property. I do not know how the topic is dealt within your texts, but the current method makes use of matrix methods : polarized light is

described using (complex) 2x2 Jones Jones matrices, partially polarized light is dealt with using 4x4 real element Mueller matrices. Any light beam polarized, unpolarized or partially polarized; is fully described by its 4 stokes parameters. Mueller marices describe operation of optical devices which operate on Stokes parameters of the in-coming light, to transform it to the out going light beam.

Lasers, non-linear optics and holography comprises again a vast arena in optics, but I have not touched it in my talk. The purpose of the talk was to give a broad picture of scope of Optics in industry, as a tool in pure science related studies, and as a branch of science itself. I leave it to your collective wisdom to frame a course suitably broken up into core and electives. In my opinion, elective courses must be Designed such that qualifies a person

for a specific profession like say optometrist at a more basic level or a designer in instrument manufacturing etc.

Optics 1

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Optics 1