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Papers by abhijit patil

Research paper thumbnail of EFFECT OF L-ARGININE ON BICALUTAMIDE COMPLEXATION WITH HYDROXYPROPYL-β-CYCLODEXTRIN

... Abhijit Patil*, Yogesh Pore, Bhanudas Kuchekar Department of Pharmaceutical Chemistry, Govern... more ... Abhijit Patil*, Yogesh Pore, Bhanudas Kuchekar Department of Pharmaceutical Chemistry, Government College of Pharmacy, Karad, Maharashtra, India, 415124 ... In IR spectra of inclusion complex (d) the peaks of bicalutamide at 3057 cm-1, 2939 cm-1, 2893 cm-1, 3577 cm-1 ...

Research paper thumbnail of Phase determination in holographic Moiré in presence of nonsinusoidal waveforms and random noise

Optics Communications, 2006

This paper proposes a subspace parameter estimation method which besides allowing for accommodati... more This paper proposes a subspace parameter estimation method which besides allowing for accommodating multiple PZTs in an optical interferometer permits for extracting in real time values of phase shifts between data frames at each pixel point. The technique enables to freely choose values ...

Research paper thumbnail of A stochastic method for generalized data reduction in holographic moir

Optics Communications, 2005

A novel generalized phase shifting method is described in this paper. The method enables the simu... more A novel generalized phase shifting method is described in this paper. The method enables the simultaneous determination of phase information carried in both moiré and carrier in holographic moiré. In holographic moiré, two simultaneous phase shifts are required for the recording of a frame. A direct stochastic algorithm for global search is applied for the exact determination of these simultaneously applied phase steps. The phase steps are varied by changing the path lengths in the interferometer by means of PZT devices, which in general show a nonlinear response. The algorithm can be utilized to characterize the nonlinear response of the PZTs and the determined phase steps are subsequently applied in a linear regression technique for the simultaneous extraction of phase information in holographic moiré. The evaluation of the algorithm has been carried out using computer generated moiré fringes.

Research paper thumbnail of Phase-shifting interferometry by a covariance-based method

Applied Optics, 2005

A novel generalized approach to phase-shifting interferometry in which phase distribution in an i... more A novel generalized approach to phase-shifting interferometry in which phase distribution in an interferogram is evaluated in the presence of nonsinusoidal waveforms and piezoactuator device miscalibration is proposed. The approach is based on the underlying rotational invariance of signal subspaces spanned by two temporally displaced data sets. The advantage of the proposed method lies in its ability to identify arbitrary phase-step values pixelwise from an interference signal buried in noise. The robustness of the proposed method is investigated by addition of white Gaussian noise during the simulations.

Research paper thumbnail of Resolution-enhanced Fourier transform method for the estimation of multiple phases in interferometry

Optics Letters, 2005

A phase shifting method based on high-resolution frequency estimation and Fourier transform techn... more A phase shifting method based on high-resolution frequency estimation and Fourier transform technique is introduced. This method, also referred to as the eigenvector method, draws on the complementary strengths of both these methods. The salient feature of the method lies in its ability to handle nonsinusoidal wave-forms, multiple piezoelectric transducers, and arbitrary phase steps in an optical configuration. The method does not need the addition of carrier fringes to separate the spectral contents in the intensity fringes. The proposed concept thus overcomes the limitations of methods based on Fourier transform techniques. The robustness of the proposed method is studied in the presence of noise.

Research paper thumbnail of Maximum-likelihood estimator for dual phase extraction in holographic moire

Optics Letters, 2005

A maximum-likelihood (ML) method based on spectral estimation theory for the extraction of dual p... more A maximum-likelihood (ML) method based on spectral estimation theory for the extraction of dual phase distributions in holographic moire in the presence of nonsinusoidal waveforms, noise, and the miscalibration of piezoelectric (PZT) devices is proposed. The extraction of these phases requires incorporating two PZTs into the moire setup. ML estimators are asymptotically efficient for sufficient data samples. The approach presented uses a direct stochastic algorithm called probabilistic global search Lausanne for minimizing the ML function.

Research paper thumbnail of Approaches in generalized phase shifting interferometry

Optics and Lasers in Engineering, 2005

A sample of phase-shifting algorithms suitable for accommodating arbitrary phase steps is passed ... more A sample of phase-shifting algorithms suitable for accommodating arbitrary phase steps is passed in review. Although not exhaustive in nature, the paper describes a wide range of concepts which have been applied to generalized phase shifting interferometry. Linear phase shift miscalibrations and nonlinear sensitivity of the piezo electric device are known to introduce errors in phase measurement. The study reveals that of the various algorithms proposed most are suitable for compensating only one of these two error sources. Application of a direct search stochastic algorithm would appear to be a promising step towards characterizing the nonlinear response of the PZT. r

Research paper thumbnail of Introduction of stochastic methods to phase-shifting interferometry

Journal of Modern Optics, 2005

1. Introduction Phase-shifting interferometry (PSI) has been used over the years because of its a... more 1. Introduction Phase-shifting interferometry (PSI) has been used over the years because of its ability to yield highly accurate phase measurements. In PSI using conventional phase-shifting techniques, the phase difference between an object and the refer-ence beam is varied ...

Research paper thumbnail of A state space approach in phase shifting interferometry

Optics Communications, 2006

The paper proposes a state space approach for the determination of phase distribution in an inter... more The paper proposes a state space approach for the determination of phase distribution in an interferogram in the presence of a nonsinusoidal waveform, random noise, and the miscalibration of the piezoelectric device. In this approach we first estimate the phase step imparted to the piezoelectric transducer (PZT) before determining the phase distribution. A denoising procedure is applied with the knowledge of the state-feedback matrix prior to the extraction of the phase step. This step ensures a good estimation of the phase distribution even at low signal-to-noise ratios. The other salient features of the proposed concept lie in its ability to compensate the detector non-linearity and in the use of non-collimated beams. The comparison of the proposed method with other bench-marking algorithms shows that our approach is efficient and robust. The experimental results show the feasibility of the proposed approach.

Research paper thumbnail of Moving ahead with phase

Optics and Lasers in Engineering, 2007

Research paper thumbnail of Chirp estimation in phase-shifting interferometry

Optics Letters, 2006

We propose a new approach for estimating the phase in the presence of a nonlinear response of a p... more We propose a new approach for estimating the phase in the presence of a nonlinear response of a phase-shifting device: a piezoelectric transducer (PZT). The method is complemented well by the high resolution and the maximum likelihood estimation techniques in the estimation of the phase step and the nonlinear coefficient. The advantage of the proposed method is that it can be extended to the extraction of multiple phases in configurations involving multiple PZTs in the presence of nonlinearity. Symmetricity in the phase steps is not required in this method. Hence hysteresis of the PZT does not have any influence on the accuracy of the phase estimation. The effectiveness of the method is shown by experimental results.

Research paper thumbnail of A min-norm approach for estimating phase distribution in an interferogram

Journal of Modern Optics, 2006

Phase distribution in an interferogram is usually computed from several phase shifted intensity i... more Phase distribution in an interferogram is usually computed from several phase shifted intensity images acquired temporally by means of a CCD camera. These phase shifts are commonly accomplished by translation of a mirror with a piezoelectric transducer (PZT). In reality the PZT motion is not exact. Thus the aim of this paper is to present a novel approach for estimating

Research paper thumbnail of Model-based processing of a holographic moir

Optics Letters, 2005

A state space model for the determination of dual phase distributions in a holographic moiré in t... more A state space model for the determination of dual phase distributions in a holographic moiré in the presence of nonsinusoidal waveforms, random noise, and miscalibration of the piezoelectric (PZT) devices is proposed. The extraction of these phase terms requires incorporating two PZTs into the moiré setup. A Toeplitz approximation method (TAM) is applied for phase determination, and modification to the Toeplitz covariance matrix formed from the phase-shifted moiré fringes by application of a denoising step in the state-feedback matrix is proposed. This step ensures that the phase terms can even be estimated at a signal-to-noise ratio much lower than that of the original TAM or by our previously suggested polynomial based method.

Research paper thumbnail of Phase-shifting interferometry in the presence of nonlinear phase steps, harmonics, and noise

Optics Letters, 2006

A phase-shifting piezo device commonly employed in phase-shifting interferometry exhibits a nonli... more A phase-shifting piezo device commonly employed in phase-shifting interferometry exhibits a nonlinear response to applied voltage. Hence, a method for estimation of phase distribution in the presence of nonlinear phase steps is presented. The proposed method compensates for the harmonics present in the intensity fringe, allows the use of arbitrary phase-step values between 0 and tau rad, and does not impose constraints on the selection of particular phase-step values for minimizing nonlinearity and compensating for the harmonics. The comparison of the proposed method with other well-known benchmarking algorithms shows that our method is highly efficient and also works well in the presence of noise.

Research paper thumbnail of Nonlinear regression technique applied to generalized phase-shifting interferometry

Journal of Modern Optics, 2005

Abstract. We develop a new approach involving nonlinear regression in phase-shifting interferomet... more Abstract. We develop a new approach involving nonlinear regression in phase-shifting interferometry with the hope of improving the accuracy of phase measurement in the presence of first-order piezoelectric transducer (PZT) calibration errors. The approach that uses the Levenberg– ...

Research paper thumbnail of Predicting phase steps in phase-shifting interferometry in the presence of noise and harmonics

Applied Optics, 2006

A novel method for estimating pixelwise phase step values in phase-shifting interferometry is pre... more A novel method for estimating pixelwise phase step values in phase-shifting interferometry is presented. The method is based on the linear prediction property of the intensity fringes recorded temporally at a pixel on the charged-coupled device. The salient features of the method lie in their ability to handle linear miscalibration errors, to compensate for the presence of harmonics in an optical configuration and detector nonlinearity, and to allow for the use of arbitrary phase steps. The robustness of the proposed method is studied in the presence of noise and a comparison with several benchmarking algorithms is performed. The simulation results show the efficiency of the algorithm in retrieving the wrapped phase.

Research paper thumbnail of Statistical study of generalized nonlinear phase step estimation methods in phase-shifting interferometry

Applied Optics, 2007

Signal processing methods based on maximum-likelihood theory, discrete chirp Fourier transform, a... more Signal processing methods based on maximum-likelihood theory, discrete chirp Fourier transform, and spectral estimation methods have enabled accurate measurement of phase in phase-shifting interferometry in the presence of nonlinear response of the piezoelectric transducer to the applied voltage. We present the statistical study of these generalized nonlinear phase step estimation methods to identify the best method by deriving the Cramér-Rao bound. We also address important aspects of these methods for implementation in practical applications and compare the performance of the best-identified method with other bench marking algorithms in the presence of harmonics and noise.

Research paper thumbnail of Phase shifting interferometry using a robust parameter estimation method

Optics and Lasers in Engineering, 2007

The paper proposes a maximum-likelihood (ML) method based on spectral estimation theory for the e... more The paper proposes a maximum-likelihood (ML) method based on spectral estimation theory for the estimation of phase distribution in interferometry in the presence of nonsinusoidal waveforms, noise, and the miscalibration of the piezoelectric device. The proposed method also allows the use of arbitrary phase steps. ML estimators are asymptotically efficient for large number of data samples. The method is complemented well by the incorporation of global search algorithm known as Probabilistic Global Search Lausanne for minimizing the ML function. The performance of the proposed method is studied in the presence of noise. r

Research paper thumbnail of A novel approach for characterizing the nonlinear phase steps of the PZT in interferometry

Optics and Lasers in Engineering, 2007

We propose a novel approach to estimate the phase distribution in the presence of nonlinear respo... more We propose a novel approach to estimate the phase distribution in the presence of nonlinear response of the PZT. The proposed method is an outcome of two different concepts based on the discrete chirp Fourier transform (DCFT) and the maximum-likelihood estimator for the estimation of nonlinear phase step. The robustness of the proposed method is tested for various magnitudes of nonlinearity and harmonics. Comparison of our proposed method with the bench marking algorithm by Hibino et al.'s six and nine sample algorithm in the presence of noise shows that our method is highly efficient. r

Research paper thumbnail of Statistical study and experimental verification of high-resolution methods in phase-shifting interferometry

Journal of The Optical Society of America A-optics Image Science and Vision, 2007

Research paper thumbnail of EFFECT OF L-ARGININE ON BICALUTAMIDE COMPLEXATION WITH HYDROXYPROPYL-β-CYCLODEXTRIN

... Abhijit Patil*, Yogesh Pore, Bhanudas Kuchekar Department of Pharmaceutical Chemistry, Govern... more ... Abhijit Patil*, Yogesh Pore, Bhanudas Kuchekar Department of Pharmaceutical Chemistry, Government College of Pharmacy, Karad, Maharashtra, India, 415124 ... In IR spectra of inclusion complex (d) the peaks of bicalutamide at 3057 cm-1, 2939 cm-1, 2893 cm-1, 3577 cm-1 ...

Research paper thumbnail of Phase determination in holographic Moiré in presence of nonsinusoidal waveforms and random noise

Optics Communications, 2006

This paper proposes a subspace parameter estimation method which besides allowing for accommodati... more This paper proposes a subspace parameter estimation method which besides allowing for accommodating multiple PZTs in an optical interferometer permits for extracting in real time values of phase shifts between data frames at each pixel point. The technique enables to freely choose values ...

Research paper thumbnail of A stochastic method for generalized data reduction in holographic moir

Optics Communications, 2005

A novel generalized phase shifting method is described in this paper. The method enables the simu... more A novel generalized phase shifting method is described in this paper. The method enables the simultaneous determination of phase information carried in both moiré and carrier in holographic moiré. In holographic moiré, two simultaneous phase shifts are required for the recording of a frame. A direct stochastic algorithm for global search is applied for the exact determination of these simultaneously applied phase steps. The phase steps are varied by changing the path lengths in the interferometer by means of PZT devices, which in general show a nonlinear response. The algorithm can be utilized to characterize the nonlinear response of the PZTs and the determined phase steps are subsequently applied in a linear regression technique for the simultaneous extraction of phase information in holographic moiré. The evaluation of the algorithm has been carried out using computer generated moiré fringes.

Research paper thumbnail of Phase-shifting interferometry by a covariance-based method

Applied Optics, 2005

A novel generalized approach to phase-shifting interferometry in which phase distribution in an i... more A novel generalized approach to phase-shifting interferometry in which phase distribution in an interferogram is evaluated in the presence of nonsinusoidal waveforms and piezoactuator device miscalibration is proposed. The approach is based on the underlying rotational invariance of signal subspaces spanned by two temporally displaced data sets. The advantage of the proposed method lies in its ability to identify arbitrary phase-step values pixelwise from an interference signal buried in noise. The robustness of the proposed method is investigated by addition of white Gaussian noise during the simulations.

Research paper thumbnail of Resolution-enhanced Fourier transform method for the estimation of multiple phases in interferometry

Optics Letters, 2005

A phase shifting method based on high-resolution frequency estimation and Fourier transform techn... more A phase shifting method based on high-resolution frequency estimation and Fourier transform technique is introduced. This method, also referred to as the eigenvector method, draws on the complementary strengths of both these methods. The salient feature of the method lies in its ability to handle nonsinusoidal wave-forms, multiple piezoelectric transducers, and arbitrary phase steps in an optical configuration. The method does not need the addition of carrier fringes to separate the spectral contents in the intensity fringes. The proposed concept thus overcomes the limitations of methods based on Fourier transform techniques. The robustness of the proposed method is studied in the presence of noise.

Research paper thumbnail of Maximum-likelihood estimator for dual phase extraction in holographic moire

Optics Letters, 2005

A maximum-likelihood (ML) method based on spectral estimation theory for the extraction of dual p... more A maximum-likelihood (ML) method based on spectral estimation theory for the extraction of dual phase distributions in holographic moire in the presence of nonsinusoidal waveforms, noise, and the miscalibration of piezoelectric (PZT) devices is proposed. The extraction of these phases requires incorporating two PZTs into the moire setup. ML estimators are asymptotically efficient for sufficient data samples. The approach presented uses a direct stochastic algorithm called probabilistic global search Lausanne for minimizing the ML function.

Research paper thumbnail of Approaches in generalized phase shifting interferometry

Optics and Lasers in Engineering, 2005

A sample of phase-shifting algorithms suitable for accommodating arbitrary phase steps is passed ... more A sample of phase-shifting algorithms suitable for accommodating arbitrary phase steps is passed in review. Although not exhaustive in nature, the paper describes a wide range of concepts which have been applied to generalized phase shifting interferometry. Linear phase shift miscalibrations and nonlinear sensitivity of the piezo electric device are known to introduce errors in phase measurement. The study reveals that of the various algorithms proposed most are suitable for compensating only one of these two error sources. Application of a direct search stochastic algorithm would appear to be a promising step towards characterizing the nonlinear response of the PZT. r

Research paper thumbnail of Introduction of stochastic methods to phase-shifting interferometry

Journal of Modern Optics, 2005

1. Introduction Phase-shifting interferometry (PSI) has been used over the years because of its a... more 1. Introduction Phase-shifting interferometry (PSI) has been used over the years because of its ability to yield highly accurate phase measurements. In PSI using conventional phase-shifting techniques, the phase difference between an object and the refer-ence beam is varied ...

Research paper thumbnail of A state space approach in phase shifting interferometry

Optics Communications, 2006

The paper proposes a state space approach for the determination of phase distribution in an inter... more The paper proposes a state space approach for the determination of phase distribution in an interferogram in the presence of a nonsinusoidal waveform, random noise, and the miscalibration of the piezoelectric device. In this approach we first estimate the phase step imparted to the piezoelectric transducer (PZT) before determining the phase distribution. A denoising procedure is applied with the knowledge of the state-feedback matrix prior to the extraction of the phase step. This step ensures a good estimation of the phase distribution even at low signal-to-noise ratios. The other salient features of the proposed concept lie in its ability to compensate the detector non-linearity and in the use of non-collimated beams. The comparison of the proposed method with other bench-marking algorithms shows that our approach is efficient and robust. The experimental results show the feasibility of the proposed approach.

Research paper thumbnail of Moving ahead with phase

Optics and Lasers in Engineering, 2007

Research paper thumbnail of Chirp estimation in phase-shifting interferometry

Optics Letters, 2006

We propose a new approach for estimating the phase in the presence of a nonlinear response of a p... more We propose a new approach for estimating the phase in the presence of a nonlinear response of a phase-shifting device: a piezoelectric transducer (PZT). The method is complemented well by the high resolution and the maximum likelihood estimation techniques in the estimation of the phase step and the nonlinear coefficient. The advantage of the proposed method is that it can be extended to the extraction of multiple phases in configurations involving multiple PZTs in the presence of nonlinearity. Symmetricity in the phase steps is not required in this method. Hence hysteresis of the PZT does not have any influence on the accuracy of the phase estimation. The effectiveness of the method is shown by experimental results.

Research paper thumbnail of A min-norm approach for estimating phase distribution in an interferogram

Journal of Modern Optics, 2006

Phase distribution in an interferogram is usually computed from several phase shifted intensity i... more Phase distribution in an interferogram is usually computed from several phase shifted intensity images acquired temporally by means of a CCD camera. These phase shifts are commonly accomplished by translation of a mirror with a piezoelectric transducer (PZT). In reality the PZT motion is not exact. Thus the aim of this paper is to present a novel approach for estimating

Research paper thumbnail of Model-based processing of a holographic moir

Optics Letters, 2005

A state space model for the determination of dual phase distributions in a holographic moiré in t... more A state space model for the determination of dual phase distributions in a holographic moiré in the presence of nonsinusoidal waveforms, random noise, and miscalibration of the piezoelectric (PZT) devices is proposed. The extraction of these phase terms requires incorporating two PZTs into the moiré setup. A Toeplitz approximation method (TAM) is applied for phase determination, and modification to the Toeplitz covariance matrix formed from the phase-shifted moiré fringes by application of a denoising step in the state-feedback matrix is proposed. This step ensures that the phase terms can even be estimated at a signal-to-noise ratio much lower than that of the original TAM or by our previously suggested polynomial based method.

Research paper thumbnail of Phase-shifting interferometry in the presence of nonlinear phase steps, harmonics, and noise

Optics Letters, 2006

A phase-shifting piezo device commonly employed in phase-shifting interferometry exhibits a nonli... more A phase-shifting piezo device commonly employed in phase-shifting interferometry exhibits a nonlinear response to applied voltage. Hence, a method for estimation of phase distribution in the presence of nonlinear phase steps is presented. The proposed method compensates for the harmonics present in the intensity fringe, allows the use of arbitrary phase-step values between 0 and tau rad, and does not impose constraints on the selection of particular phase-step values for minimizing nonlinearity and compensating for the harmonics. The comparison of the proposed method with other well-known benchmarking algorithms shows that our method is highly efficient and also works well in the presence of noise.

Research paper thumbnail of Nonlinear regression technique applied to generalized phase-shifting interferometry

Journal of Modern Optics, 2005

Abstract. We develop a new approach involving nonlinear regression in phase-shifting interferomet... more Abstract. We develop a new approach involving nonlinear regression in phase-shifting interferometry with the hope of improving the accuracy of phase measurement in the presence of first-order piezoelectric transducer (PZT) calibration errors. The approach that uses the Levenberg– ...

Research paper thumbnail of Predicting phase steps in phase-shifting interferometry in the presence of noise and harmonics

Applied Optics, 2006

A novel method for estimating pixelwise phase step values in phase-shifting interferometry is pre... more A novel method for estimating pixelwise phase step values in phase-shifting interferometry is presented. The method is based on the linear prediction property of the intensity fringes recorded temporally at a pixel on the charged-coupled device. The salient features of the method lie in their ability to handle linear miscalibration errors, to compensate for the presence of harmonics in an optical configuration and detector nonlinearity, and to allow for the use of arbitrary phase steps. The robustness of the proposed method is studied in the presence of noise and a comparison with several benchmarking algorithms is performed. The simulation results show the efficiency of the algorithm in retrieving the wrapped phase.

Research paper thumbnail of Statistical study of generalized nonlinear phase step estimation methods in phase-shifting interferometry

Applied Optics, 2007

Signal processing methods based on maximum-likelihood theory, discrete chirp Fourier transform, a... more Signal processing methods based on maximum-likelihood theory, discrete chirp Fourier transform, and spectral estimation methods have enabled accurate measurement of phase in phase-shifting interferometry in the presence of nonlinear response of the piezoelectric transducer to the applied voltage. We present the statistical study of these generalized nonlinear phase step estimation methods to identify the best method by deriving the Cramér-Rao bound. We also address important aspects of these methods for implementation in practical applications and compare the performance of the best-identified method with other bench marking algorithms in the presence of harmonics and noise.

Research paper thumbnail of Phase shifting interferometry using a robust parameter estimation method

Optics and Lasers in Engineering, 2007

The paper proposes a maximum-likelihood (ML) method based on spectral estimation theory for the e... more The paper proposes a maximum-likelihood (ML) method based on spectral estimation theory for the estimation of phase distribution in interferometry in the presence of nonsinusoidal waveforms, noise, and the miscalibration of the piezoelectric device. The proposed method also allows the use of arbitrary phase steps. ML estimators are asymptotically efficient for large number of data samples. The method is complemented well by the incorporation of global search algorithm known as Probabilistic Global Search Lausanne for minimizing the ML function. The performance of the proposed method is studied in the presence of noise. r

Research paper thumbnail of A novel approach for characterizing the nonlinear phase steps of the PZT in interferometry

Optics and Lasers in Engineering, 2007

We propose a novel approach to estimate the phase distribution in the presence of nonlinear respo... more We propose a novel approach to estimate the phase distribution in the presence of nonlinear response of the PZT. The proposed method is an outcome of two different concepts based on the discrete chirp Fourier transform (DCFT) and the maximum-likelihood estimator for the estimation of nonlinear phase step. The robustness of the proposed method is tested for various magnitudes of nonlinearity and harmonics. Comparison of our proposed method with the bench marking algorithm by Hibino et al.'s six and nine sample algorithm in the presence of noise shows that our method is highly efficient. r

Research paper thumbnail of Statistical study and experimental verification of high-resolution methods in phase-shifting interferometry

Journal of The Optical Society of America A-optics Image Science and Vision, 2007