Rajpal Sirohi - Academia.edu (original) (raw)

Papers by Rajpal Sirohi

Springer proceedings in physics, 2017

Coloured fringes seen in white light when the two glass plates in near contact enclose a very sma... more Coloured fringes seen in white light when the two glass plates in near contact enclose a very small angle were first observed by Boyle and independently by Hooke in the later part of 17th century and the explanation given using wave theory of light could be taken as the starting point of optical interferometry. Wave theory used by Boyle and Hooke, and in much refined form as proposed by Huygens in 1690 remained unaccepted until Young in 1801 demonstrated the interference between two waves by a very simple but ingenious way. Fizeau (Acad Sci 66:429, 1862 [1]) carried out experiments with a pair of plates using Na light and showed that the fringe pattern disappears when a certain distance separates the plates, essentially sowing the seeds for interference spectroscopy. Michelson in 1891 carried out measurement of visibility of fringes as a function of path difference between the two beams derived from various sources and showed that except for cadmium, other spectral lines showed the variation in visibility. Fizeau is also accredited to have suggested in 1868 that interferometry may be used for measuring stellar dimensions: the idea being taken forward by Michelson by inventing stellar interferometer. The manuscript presents the chronology of development in interferometry. Some current applications may also be highlighted.

Asian Journal of Physics

Optical instruments are used for observation and spectroscopy apart from host of many other appli... more Optical instruments are used for observation and spectroscopy apart from host of many other applications. Both in observation and spectroscopy it is important to know how closely two objects, or two spectral lines can be resolved by the instruments. There had been a number of criteria of resolution: two most often used are Rayleigh criterion and Sparrow criterion. Rayleigh criterion of resolution has no mathematical support but is often used due to its simplicity. Sparrow criterion gives the lowest limit of resolution. Further in seeing, the nature of illumination of the object has profound effect on the limit of resolution. Rayleigh criterion tacitfully assumes incoherent illumination, while the Sparrow criterion can be applied to incoherent, partially coherent and coherent illuminations. Applicability of Rayleigh criterion can be extended to partially coherent and incoherent illuminations by a simple modification. The paper through the tutorial approach describes the resolution of optical instruments used for seeing and spectroscopy.

Asian Journal of Physics

The paper endeavours the history of light and optics from the early Greek period and discusses th... more The paper endeavours the history of light and optics from the early Greek period and discusses the contributions made by philosophers and later by scientists in understanding the properties of light. Many of the thoughts expressed by Philosophers and Scientists about the nature of light have been taken from the Internet.

Asian Journal of Physics

Optical interferometry is perhaps the oldest precision measurement technique that has evolved in ... more Optical interferometry is perhaps the oldest precision measurement technique that has evolved in its various variants due to the developments in optical sources and detector systems, and varied applications. Some of the variants are developed to enhance the accuracy of measurement and also the ease of measurement. This paper discusses the theory of multi-pass, multi-beam and multi-wavelength interferometries. ©

Asian Journal of Physics

Focal length of an imaging system is an important parameter as it determines its gathering power,... more Focal length of an imaging system is an important parameter as it determines its gathering power, numerical aperture and resolution. Its determination becomes very difficult as one of the planes is not physically accessible. A number of methods have been developed that measure either the effective focal length or the back focal length. The objective of the present paper is to discuss various methods that have been investigated and reported in the literature.

Asian Journal of Physics, 2019

A number of phase-shift algorithms exist in literature. These are categorized as 3-step, 4-step, ... more A number of phase-shift algorithms exist in literature. These are categorized as 3-step, 4-step, 5-step etc. with different but constant values of phase steps. In this paper, it is shown that many of them can be deduced from the generalized theory under each category in literature.

Field Guide to Optics Education: A Tribute to John Greivenkamp

Optik - International Journal for Light and Electron Optics, 2011

Optics Communications, 1996

Leendertz two-beam illumination and Duffy's two-aperture arrangements are two well establish... more Leendertz two-beam illumination and Duffy's two-aperture arrangements are two well established optical configurations in speckle interferometry for in-plane displacement measurement. However, the measurement sensitivities of both these techniques are quite different. In Leendertz method the interbeam angle between the two illumination beams determines the sensitivity, while in Duffy's arrangement, it is governed by the subtense formed by aperture separation at the object. In the present paper, we implement both these configurations simultaneously for in-plane displacement measurement. The proposed optical arrangement extends the range of in-plane displacement measurement considerably. Detailed theoretical and experimental results are presented.

Journal of the Optical Society of America A, 1988

Applied Optics, 1971

Ellipsometry is being used increasingly for the study of surfaces and/or films on the absorbing o... more Ellipsometry is being used increasingly for the study of surfaces and/or films on the absorbing or nonabsorbing substrates (Refs. 1 and 2 and the references cited therein). The technique is precise and can be employed in in situ studies and yields unique values of surface constants and dielectric film parameters. However, for an absorbing film an estimate of one of the three unknown param­ eters is required. The usual method for obtaining the surface constants involves the measurements of Δ (phase change) and ψ (amplitude diminu­ tion) values for a fixed and known value of the angle of incidence. The optical constants are then obtained by substituting these measured quantities in the following equations:

Asian Journal of Physics, 2014

The paper discusses the theory of digital shear speckle pattern interferometry (DSSPI). DSSPI is ... more The paper discusses the theory of digital shear speckle pattern interferometry (DSSPI). DSSPI is used mainly for nondestructive testing but can also be used for quantitative evaluation of strains, slopes and curvatures. Use of holo-and/or diffractive elements due to their multi-function capabilities makes their use in DSSPI attractive.

Asian Journal of Physics, 2015

Radius of curvature of spherical surfaces and the focal length of optical imaging systems are ver... more Radius of curvature of spherical surfaces and the focal length of optical imaging systems are very important parameters to be measured. Large number of techniques and methods have been developed over the years. They offer varying accuracy and ranges. However, the complexities of measurement increase depending on the desired accuracy and range. The paper presents a variety of techniques and methods that include contact type and non-contact type methods.

Asian Journal of Physics, 2019

A number of phase-shift algorithms exist in literature. These are categorized as 3-step, 4-step, ... more A number of phase-shift algorithms exist in literature. These are categorized as 3-step, 4-step, 5-step etc. with different but constant values of phase steps. In this paper, it is shown that many of them can be deduced from the generalized theory under each category in literature.

Asian Journal of Physics, 2022

Focal length of an imaging system is an important parameter as it determines its gathering power,... more Focal length of an imaging system is an important parameter as it determines its gathering power, numerical aperture and resolution. Its determination becomes very difficult as one of the planes is not physically accessible. A number of methods have been developed that measure either the effective focal length or the back focal length. The objective of the present paper is to discuss various methods that have been investigated and reported in the literature.

Asian Journal of Physics, 2019

The paper endeavours the history of light and optics from the early Greek period and discusses th... more The paper endeavours the history of light and optics from the early Greek period and discusses the contributions made by philosophers and later by scientists in understanding the properties of light. Many of the thoughts expressed by Philosophers and Scientists about the nature of light have been taken from the Internet.

Asian Journal of Physics, 2019

Optical interferometry is perhaps the oldest precision measurement technique that has evolved in ... more Optical interferometry is perhaps the oldest precision measurement technique that has evolved in its various variants due to the developments in optical sources and detector systems, and varied applications. Some of the variants are developed to enhance the accuracy of measurement and also the ease of measurement. This paper discusses the theory of multi-pass, multi-beam and multi-wavelength interferometries. ©

Asian Journal of Physics, 2021

Optical instruments are used for observation and spectroscopy apart from host of many other appli... more Optical instruments are used for observation and spectroscopy apart from host of many other applications. Both in observation and spectroscopy it is important to know how closely two objects, or two spectral lines can be resolved by the instruments. There had been a number of criteria of resolution: two most often used are Rayleigh criterion and Sparrow criterion. Rayleigh criterion of resolution has no mathematical support but is often used due to its simplicity. Sparrow criterion gives the lowest limit of resolution. Further in seeing, the nature of illumination of the object has profound effect on the limit of resolution. Rayleigh criterion tacitfully assumes incoherent illumination, while the Sparrow criterion can be applied to incoherent, partially coherent and coherent illuminations. Applicability of Rayleigh criterion can be extended to partially coherent and incoherent illuminations by a simple modification. The paper through the tutorial approach describes the resolution of optical instruments used for seeing and spectroscopy.

Light: Advanced Manufacturing, 2021

This paper presents the activities in the field of shearography in chronological order and highli... more This paper presents the activities in the field of shearography in chronological order and highlights the great potential of this holographic measurement technology. After a brief introduction, the basic theory of shearography is presented. Shear devices, phase-shift arrangements, and multiplexed shearography systems are described. Finally, the application areas where shearography has been accepted and successfully used as a tool are presented.

Springer proceedings in physics, 2017

Coloured fringes seen in white light when the two glass plates in near contact enclose a very sma... more Coloured fringes seen in white light when the two glass plates in near contact enclose a very small angle were first observed by Boyle and independently by Hooke in the later part of 17th century and the explanation given using wave theory of light could be taken as the starting point of optical interferometry. Wave theory used by Boyle and Hooke, and in much refined form as proposed by Huygens in 1690 remained unaccepted until Young in 1801 demonstrated the interference between two waves by a very simple but ingenious way. Fizeau (Acad Sci 66:429, 1862 [1]) carried out experiments with a pair of plates using Na light and showed that the fringe pattern disappears when a certain distance separates the plates, essentially sowing the seeds for interference spectroscopy. Michelson in 1891 carried out measurement of visibility of fringes as a function of path difference between the two beams derived from various sources and showed that except for cadmium, other spectral lines showed the variation in visibility. Fizeau is also accredited to have suggested in 1868 that interferometry may be used for measuring stellar dimensions: the idea being taken forward by Michelson by inventing stellar interferometer. The manuscript presents the chronology of development in interferometry. Some current applications may also be highlighted.

Asian Journal of Physics

Optical instruments are used for observation and spectroscopy apart from host of many other appli... more Optical instruments are used for observation and spectroscopy apart from host of many other applications. Both in observation and spectroscopy it is important to know how closely two objects, or two spectral lines can be resolved by the instruments. There had been a number of criteria of resolution: two most often used are Rayleigh criterion and Sparrow criterion. Rayleigh criterion of resolution has no mathematical support but is often used due to its simplicity. Sparrow criterion gives the lowest limit of resolution. Further in seeing, the nature of illumination of the object has profound effect on the limit of resolution. Rayleigh criterion tacitfully assumes incoherent illumination, while the Sparrow criterion can be applied to incoherent, partially coherent and coherent illuminations. Applicability of Rayleigh criterion can be extended to partially coherent and incoherent illuminations by a simple modification. The paper through the tutorial approach describes the resolution of optical instruments used for seeing and spectroscopy.

Asian Journal of Physics

The paper endeavours the history of light and optics from the early Greek period and discusses th... more The paper endeavours the history of light and optics from the early Greek period and discusses the contributions made by philosophers and later by scientists in understanding the properties of light. Many of the thoughts expressed by Philosophers and Scientists about the nature of light have been taken from the Internet.

Asian Journal of Physics

Optical interferometry is perhaps the oldest precision measurement technique that has evolved in ... more Optical interferometry is perhaps the oldest precision measurement technique that has evolved in its various variants due to the developments in optical sources and detector systems, and varied applications. Some of the variants are developed to enhance the accuracy of measurement and also the ease of measurement. This paper discusses the theory of multi-pass, multi-beam and multi-wavelength interferometries. ©

Asian Journal of Physics

Focal length of an imaging system is an important parameter as it determines its gathering power,... more Focal length of an imaging system is an important parameter as it determines its gathering power, numerical aperture and resolution. Its determination becomes very difficult as one of the planes is not physically accessible. A number of methods have been developed that measure either the effective focal length or the back focal length. The objective of the present paper is to discuss various methods that have been investigated and reported in the literature.

Asian Journal of Physics, 2019

A number of phase-shift algorithms exist in literature. These are categorized as 3-step, 4-step, ... more A number of phase-shift algorithms exist in literature. These are categorized as 3-step, 4-step, 5-step etc. with different but constant values of phase steps. In this paper, it is shown that many of them can be deduced from the generalized theory under each category in literature.

Field Guide to Optics Education: A Tribute to John Greivenkamp

Optik - International Journal for Light and Electron Optics, 2011

Optics Communications, 1996

Leendertz two-beam illumination and Duffy's two-aperture arrangements are two well establish... more Leendertz two-beam illumination and Duffy's two-aperture arrangements are two well established optical configurations in speckle interferometry for in-plane displacement measurement. However, the measurement sensitivities of both these techniques are quite different. In Leendertz method the interbeam angle between the two illumination beams determines the sensitivity, while in Duffy's arrangement, it is governed by the subtense formed by aperture separation at the object. In the present paper, we implement both these configurations simultaneously for in-plane displacement measurement. The proposed optical arrangement extends the range of in-plane displacement measurement considerably. Detailed theoretical and experimental results are presented.

Journal of the Optical Society of America A, 1988

Applied Optics, 1971

Ellipsometry is being used increasingly for the study of surfaces and/or films on the absorbing o... more Ellipsometry is being used increasingly for the study of surfaces and/or films on the absorbing or nonabsorbing substrates (Refs. 1 and 2 and the references cited therein). The technique is precise and can be employed in in situ studies and yields unique values of surface constants and dielectric film parameters. However, for an absorbing film an estimate of one of the three unknown param­ eters is required. The usual method for obtaining the surface constants involves the measurements of Δ (phase change) and ψ (amplitude diminu­ tion) values for a fixed and known value of the angle of incidence. The optical constants are then obtained by substituting these measured quantities in the following equations:

Asian Journal of Physics, 2014

The paper discusses the theory of digital shear speckle pattern interferometry (DSSPI). DSSPI is ... more The paper discusses the theory of digital shear speckle pattern interferometry (DSSPI). DSSPI is used mainly for nondestructive testing but can also be used for quantitative evaluation of strains, slopes and curvatures. Use of holo-and/or diffractive elements due to their multi-function capabilities makes their use in DSSPI attractive.

Asian Journal of Physics, 2015

Radius of curvature of spherical surfaces and the focal length of optical imaging systems are ver... more Radius of curvature of spherical surfaces and the focal length of optical imaging systems are very important parameters to be measured. Large number of techniques and methods have been developed over the years. They offer varying accuracy and ranges. However, the complexities of measurement increase depending on the desired accuracy and range. The paper presents a variety of techniques and methods that include contact type and non-contact type methods.

Asian Journal of Physics, 2019

A number of phase-shift algorithms exist in literature. These are categorized as 3-step, 4-step, ... more A number of phase-shift algorithms exist in literature. These are categorized as 3-step, 4-step, 5-step etc. with different but constant values of phase steps. In this paper, it is shown that many of them can be deduced from the generalized theory under each category in literature.

Asian Journal of Physics, 2022

Focal length of an imaging system is an important parameter as it determines its gathering power,... more Focal length of an imaging system is an important parameter as it determines its gathering power, numerical aperture and resolution. Its determination becomes very difficult as one of the planes is not physically accessible. A number of methods have been developed that measure either the effective focal length or the back focal length. The objective of the present paper is to discuss various methods that have been investigated and reported in the literature.

Asian Journal of Physics, 2019

The paper endeavours the history of light and optics from the early Greek period and discusses th... more The paper endeavours the history of light and optics from the early Greek period and discusses the contributions made by philosophers and later by scientists in understanding the properties of light. Many of the thoughts expressed by Philosophers and Scientists about the nature of light have been taken from the Internet.

Asian Journal of Physics, 2019

Optical interferometry is perhaps the oldest precision measurement technique that has evolved in ... more Optical interferometry is perhaps the oldest precision measurement technique that has evolved in its various variants due to the developments in optical sources and detector systems, and varied applications. Some of the variants are developed to enhance the accuracy of measurement and also the ease of measurement. This paper discusses the theory of multi-pass, multi-beam and multi-wavelength interferometries. ©

Asian Journal of Physics, 2021

Optical instruments are used for observation and spectroscopy apart from host of many other appli... more Optical instruments are used for observation and spectroscopy apart from host of many other applications. Both in observation and spectroscopy it is important to know how closely two objects, or two spectral lines can be resolved by the instruments. There had been a number of criteria of resolution: two most often used are Rayleigh criterion and Sparrow criterion. Rayleigh criterion of resolution has no mathematical support but is often used due to its simplicity. Sparrow criterion gives the lowest limit of resolution. Further in seeing, the nature of illumination of the object has profound effect on the limit of resolution. Rayleigh criterion tacitfully assumes incoherent illumination, while the Sparrow criterion can be applied to incoherent, partially coherent and coherent illuminations. Applicability of Rayleigh criterion can be extended to partially coherent and incoherent illuminations by a simple modification. The paper through the tutorial approach describes the resolution of optical instruments used for seeing and spectroscopy.

Light: Advanced Manufacturing, 2021

This paper presents the activities in the field of shearography in chronological order and highli... more This paper presents the activities in the field of shearography in chronological order and highlights the great potential of this holographic measurement technology. After a brief introduction, the basic theory of shearography is presented. Shear devices, phase-shift arrangements, and multiplexed shearography systems are described. Finally, the application areas where shearography has been accepted and successfully used as a tool are presented.