数字全息显微术与白光相移干涉法的比较
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dard 8 bits black and white CCD camera with 4.65 lm pixel
size. Each reference arm is adjusted carefully to match the optical path length of the corresponding object arm, in order to create an interference pattern on the CCD for both wavelengths. By tilting the mirror M1 for the first wavelength reference beam and the pair of mirrors M2 and M3 for the second one as shown in Fig. 1a, one can find finely tune each k-vector incident upon the CCD camera. The CCD camera records the digital hologram that result from the interference between the object wave O1 and the reference wave R1. And also, the interference between
2. Experimental setup
The optical setup is depicted in Fig. 1a, with the laser diodes sources at k1 ¼ 635 nm and k2 ¼ 675 nm, yielding
a synthetic wavelength K = 10.72 lm. The key concept of
Keywords: Digital holography Interferometry Phase shifting
abstract
This paper presents a quantitative comparison between off-axis digital holographic microscopy (DHM) and on-axis phase-shifting interferometry (PSI) for surface micro topography
Biblioteka Baidu
beam pair in different reference arms, while combining them in an object arm. Fig. 1b illustrates the schematic diagram of the dual-wavelength, off-axis DHM. Results presented here have been obtained with a microscope objective (MO) of magnification 4Â with a NA of 0.25 and working distance WD of 10.6 mm. After reflection on the sample as shown in Fig. 1b, both collinear object wave-fronts are collected by the MO (infinity-corrected), and the object images are formed by an imaging lens about 50 mm behind the CCD plane. The CCD camera is a stan-
principle of the main setup of Fig. 1a is described in details for macro scale in Refs. [3,4]. In case of single shot, dualwavelength, off-axis DHM, the procedure for hologram processing, in particular for phase reconstruction, is described
measurement. The comparison has been applied on an object of a 1.34 lm nominal step
height. The experimental results show that single shot, dual-wavelength, off-axis DHM surpasses on dual-wavelength, on-axis PSI in terms of accuracy and repeatability.
applied on an object of a 1.34 lm nominal step height.
Off-axis DHM and on-axis PSI configurations used for the present study are shown in Fig. 1b and c, respectively. The
D.G. Abdelsalam
Engineering and Surface Metrology Lab., National Institute of Standards, Tersa St., El Haram, El Giza, Egypt
article info
Article history: Received 17 March 2013 Received in revised form 5 July 2013 Accepted 15 July 2013 Available online 25 July 2013
Measurement 46 (2013) 4121–4126
Contents lists available at ScienceDirect
Measurement
journal homepage: www.elsevier.com/locate/measurement
A comparison of digital holographic microscopy and on-axis phase-shifting interferometry for surface profiling
in detail in Refs. [5–7]. In case of in-line PSI, 4p/2 phase-
shifted frames performed using piezoelectric transducer (PZT) has been stored for each wavelength separately. The process of image acquisition with phase shifting is carried out with a homemade program. The four-step phase shifting algorithm has been used to reconstruct the phase object for each wavelength separately. The flat fielding method has been used to suppress the noise in phase contrast image [8–11]. The independent phase maps after noise suppression are subtracted and a phase map for the beat-wavelength is obtained and converted to height map. The experimental results show that single shot, dual-wavelength, off-axis DHM offers higher performance in terms of accuracy and repeatability.
the proposed scheme is to separate each wave wavelength
4122
D.G. Abdelsalam / Measurement 46 (2013) 4121–4126
Fig. 1. Optical arrangement, (a) the proposed schematic diagram, (b) schematic diagram of the dual-wavelength, off-axis DHM, and (c) schematic diagram of the dual-wavelength in-line PSI.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Optical methods have been used as metrological tools for a long time [1]. Among these optical methods, Digital holographic microscopy (DHM) and phase-shifting interferometry (PSI) have received much interest for surface micro topography measurement. Compared to classical phaseshifting interferometric techniques, DHM enables the extraction of both amplitude and phase information of a wave diffracted by a specimen sample from a single hologram with high resolution [2–4]. One of the compelling advantages of DHM is that the measurements are performed much faster, as the complete description of the complex wave-front is obtained from a single hologram capture, while at least three acquisitions are required with phase shifting techniques. This signifies that the DHM technique is less sensitive to the external perturbations (vibration and ambient light), since the capture time is reduced to a few microseconds. In this paper, we present a quantitative comparison between off-axis DHM and on-axis PSI methods
E-mail address: shosho_dahi@yahoo.com
0263-2241/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2013.07.026
size. Each reference arm is adjusted carefully to match the optical path length of the corresponding object arm, in order to create an interference pattern on the CCD for both wavelengths. By tilting the mirror M1 for the first wavelength reference beam and the pair of mirrors M2 and M3 for the second one as shown in Fig. 1a, one can find finely tune each k-vector incident upon the CCD camera. The CCD camera records the digital hologram that result from the interference between the object wave O1 and the reference wave R1. And also, the interference between
2. Experimental setup
The optical setup is depicted in Fig. 1a, with the laser diodes sources at k1 ¼ 635 nm and k2 ¼ 675 nm, yielding
a synthetic wavelength K = 10.72 lm. The key concept of
Keywords: Digital holography Interferometry Phase shifting
abstract
This paper presents a quantitative comparison between off-axis digital holographic microscopy (DHM) and on-axis phase-shifting interferometry (PSI) for surface micro topography
Biblioteka Baidu
beam pair in different reference arms, while combining them in an object arm. Fig. 1b illustrates the schematic diagram of the dual-wavelength, off-axis DHM. Results presented here have been obtained with a microscope objective (MO) of magnification 4Â with a NA of 0.25 and working distance WD of 10.6 mm. After reflection on the sample as shown in Fig. 1b, both collinear object wave-fronts are collected by the MO (infinity-corrected), and the object images are formed by an imaging lens about 50 mm behind the CCD plane. The CCD camera is a stan-
principle of the main setup of Fig. 1a is described in details for macro scale in Refs. [3,4]. In case of single shot, dualwavelength, off-axis DHM, the procedure for hologram processing, in particular for phase reconstruction, is described
measurement. The comparison has been applied on an object of a 1.34 lm nominal step
height. The experimental results show that single shot, dual-wavelength, off-axis DHM surpasses on dual-wavelength, on-axis PSI in terms of accuracy and repeatability.
applied on an object of a 1.34 lm nominal step height.
Off-axis DHM and on-axis PSI configurations used for the present study are shown in Fig. 1b and c, respectively. The
D.G. Abdelsalam
Engineering and Surface Metrology Lab., National Institute of Standards, Tersa St., El Haram, El Giza, Egypt
article info
Article history: Received 17 March 2013 Received in revised form 5 July 2013 Accepted 15 July 2013 Available online 25 July 2013
Measurement 46 (2013) 4121–4126
Contents lists available at ScienceDirect
Measurement
journal homepage: www.elsevier.com/locate/measurement
A comparison of digital holographic microscopy and on-axis phase-shifting interferometry for surface profiling
in detail in Refs. [5–7]. In case of in-line PSI, 4p/2 phase-
shifted frames performed using piezoelectric transducer (PZT) has been stored for each wavelength separately. The process of image acquisition with phase shifting is carried out with a homemade program. The four-step phase shifting algorithm has been used to reconstruct the phase object for each wavelength separately. The flat fielding method has been used to suppress the noise in phase contrast image [8–11]. The independent phase maps after noise suppression are subtracted and a phase map for the beat-wavelength is obtained and converted to height map. The experimental results show that single shot, dual-wavelength, off-axis DHM offers higher performance in terms of accuracy and repeatability.
the proposed scheme is to separate each wave wavelength
4122
D.G. Abdelsalam / Measurement 46 (2013) 4121–4126
Fig. 1. Optical arrangement, (a) the proposed schematic diagram, (b) schematic diagram of the dual-wavelength, off-axis DHM, and (c) schematic diagram of the dual-wavelength in-line PSI.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Optical methods have been used as metrological tools for a long time [1]. Among these optical methods, Digital holographic microscopy (DHM) and phase-shifting interferometry (PSI) have received much interest for surface micro topography measurement. Compared to classical phaseshifting interferometric techniques, DHM enables the extraction of both amplitude and phase information of a wave diffracted by a specimen sample from a single hologram with high resolution [2–4]. One of the compelling advantages of DHM is that the measurements are performed much faster, as the complete description of the complex wave-front is obtained from a single hologram capture, while at least three acquisitions are required with phase shifting techniques. This signifies that the DHM technique is less sensitive to the external perturbations (vibration and ambient light), since the capture time is reduced to a few microseconds. In this paper, we present a quantitative comparison between off-axis DHM and on-axis PSI methods
E-mail address: shosho_dahi@yahoo.com
0263-2241/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2013.07.026