- Email: [email protected]
Study of non-classical light imaging technology
Nuclear Instruments and Methods in Physics Research A 637 (2011) S130–S133
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Study of non-classical light imaging technology Ming-rui Chen a,b,, Si-wen Bi a, Xi-bo Dou a,b, Wang-yun Liu a a b
State Key Laboratory of Transient Optics and Photonics, Chinese Academy of Sciences, Xi’an, 710119, China Graduate University of Chinese Academy of Sciences, Beijing, 100049, China
a r t i c l e in f o
a b s t r a c t
Available online 10 February 2010
Non-classical light that generates through the optical parametric down-conversion process by using an optical parametric oscillator is introduced, and the imaging system based on the light is built. The characteristics of the light and the spatial resolution of the image are studied. The light irradiates directly on the object plate, producing a mass of signal photons, then the signal photons are collected by the charge-coupled device. The output electrical signal is collected by a high-speed data collection card and processed with software. Finally, the object image is acquired, and its revised image is obtained by image processing. The results indicate that the resolution of the image based on the non-classical infrared light is 1.43 times that of infrared coherent light. The non-classical light can be widely used for high-resolution imaging, spectrum analysis, and micro-biological sample detection. & 2010 Elsevier B.V. All rights reserved.
Keywords: Imaging technology Non-classical light High-resolution Parametric down-conversion
1. Introduction In the last few years, there has been an increased interest in high-resolution and high signal-to-noise ratio imaging technology. Photoelectric imaging detection systems [1], such as surveillance, search, capture, and tracking, function as passive imaging detection. The passive imaging systems do not work well when the reflected signal energy is very weak. The shortcomings may be overcome by using an artificial optical radiation source [2,3]. However, the resolution of the imaging system cannot be improved continually because of the influence of the classical diffraction limit and quantum noise limit. From a quantum point of view, they must be described by a quantum state that spans over as many transverse modes as pixels [4]. Most quantum imaging ideas and experiments aim to generate the non-classical states of light that are needed in imaging [5,6]. Squeezed light is an important non-classical light that can overcome the laser shotnoise and quantum noise [7]. Recent proposals include the use of squeezed light beams. These beams display a quantum noise reduction in several portions of the transverse section in order to increase the resolution of image detection [8]. Additionally, squeezed light beams offer the possibility of quantum teleportation [9] or, in general, quantum computation [10] and parallel teleportation of quantum information by using either local squeezing or local entanglement [11].
Corresponding author at: State Key Laboratory of Transient Optics and Photonics, Chinese Academy of Sciences, Xi’an, 710119, China. Fax: + 86 29 88887603. E-mail address: [email protected] (M.-r. Chen).
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.02.039
An ideal candidate for generating squeezed light is parametric down-conversion by utilizing a nonlinear crystal, such as the periodically poled KTiOPO4, LiNbO3, KNbO3, and so forth [12]. The phase difference caused by diffraction is compensated by a nonlinear optical coefficient, and the walk-off effect of the crystal is also suppressed. Moreover, the KTiOPO4 crystal, with a larger spectral bandwidth and high transform coefficient, may be used at room temperature. The paper focuses on active imaging technology with nonclassical light. The generation of the light source, structure of the imaging system, working principle, and spatial resolution are also introduced. A target object image of non-classical light is acquired, and its revised image is obtained by image processing. The spatial resolution of this system can reach 10 LP/mm, as tested with a resolution board. The system can be widely used for very faint luminescence detecting, biological luminescence, and weak light detection.
2. Experiment setup A schematic of the imaging system is shown in Fig. 1. The system consists of a laser, a series of non-classical generating equipment, a double glue lens, a hyper-hemispherical submersed lens, a charge-coupled device (CCD), and a laptop computer. The output of the laser is fed into a pumped parametric oscillator (OPO), which provides the near infrared. The light irradiates directly on the object plate, producing a mass of signal photons, then the signal photons are collected by the CCD. The output electrical signal is collected by a high-speed data collection card
M.-r. Chen et al. / Nuclear Instruments and Methods in Physics Research A 637 (2011) S130–S133
S131
OPO Laser
Signal collected&processed
OPO
R2 Object Lens
CCD
H 4 FR
PC
H5
f4
M1
M2
Nd:YAG Laser
Fig. 1. Imaging system with squeezed light.
f1
H1
f2
f3
H 2 P2 H 3
P1
FP
Nonlinear crystal bˆ p
aˆi
aˆs
R1
Fig. 3. System of squeezed light.
Fig. 2. Generation of squeezed light.
and processed with software. Finally, the object image is acquired, and its revised image is obtained by image processing.
O
n’ R
2.1. Non-classical light source Fig. 2 shows the generation of squeezed light. A parametric down-converter essentially consists of two modes, usually called the signal mode and idler mode, coupled through a nonlinear crystal with a w(2) coefficient [13]. Here, a^ and b^ are the annihilation operators for the signal and pump modes, respectively. The Hamiltonian for degenerate parametric down-conversion is: ^ ^ ¼ ‘ oa^ þ a^ þ ‘ op b^ þ b^ þ i‘ wð2Þ ða^ 2 b^ þ a^ þ 2 bÞ: H
n B A
L’ L Fig. 4. Photoelectron detection with a hyper-hemispherical lens.
ð1Þ
In the parametric approximation, the pump field is treated classically, and the pump depletion is neglected. We assume that þ b^ and b^ are beiwp t and b eiwp t , respectively. The Hamiltonian in Eq. (1) becomes: ^ ðPAÞ ¼ ‘ oa^ þ a^ þ i‘ ðZ a^ 2 eiwp t Za^ þ 2 eiwp t Þ H
ð2Þ
(2)
where Z = w b. The Hamiltonian for the degenerate parametric down-converter, in the interaction picture, is: ^ I ðtÞ ¼ i‘ ½Z a^ 2 eiðop 2oÞt Za^ þ 2 eiðop 2oÞt : H
ð3Þ
Fig. 5. Data-collected software.
When the pump and signal frequencies satisfy op = 2o, we have: ^ I ¼ i‘ ðZ a^ 2 Za^ þ 2 Þ: H
ð4Þ
We then obtain: ^ I t=‘ Þ ¼ expðZ t a^ 2 Zt a^ þ 2 Þ: U^ I ðt; 0Þ ¼ expðiH Assuming that x = 2Zt, we can write: 1 1 ^ xÞ: x a^ 2 xa^ þ 2 ¼ Sð U^ I ðt; 0Þ ¼ exp 2 2
ð5Þ
ð6Þ
It is clear from Eq. (6) that squeezing is presented in the nonlinear optical processes. The laser is an amplified Nd:YAG continuous wave, single frequency system (INNOLIGHT DIABOLO) that delivers a beam at 1064 nm with 400 mW of average power and a beam at 532 nm with 800 mW of average power. The frequency stability is less than 2 MHz/min, and the long-term stability of the beam is less than 70.5%, respectively. The power of the light is controlled by optical equipment that consists of a half wave plate and a beam splitter. The infrared and the green light are fed into a synchronously pumped parametric oscillator that provides a signal beam at 1064 nm with 20 uW of average power and an
idler beam near 532 nm (not used). A schematic of the experiment setup is shown in Fig. 3. The curvature radius of the input mirror, M1, is 30 mm; the reflection of infrared light is 99.5%; and the transmission of green light is about 70%. The plane has a high transmission with both beams. The curvature radius of the output mirror, M2, is also 30 mm; the transmission of infrared light is 13.5%; and the reflection of green light is about 90%. The plane has a high transmission with infrared light. The size of the periodically polarized KTiOPO4 is l 2 12 mm. A piezoelectric transducer (PZT) is attached to mirror M1 for scanning of the cavity length. The distortion of the PZT can be utilized in the frequency stabilizing of the OPO cavity to keep the center of its resonant frequency unchanged.
2.2. Characteristics of the hyper-hemispherical submersed lens The hyper-hemispherical submersed lens in front of the CCD is used to improve the signal-to-noise ratio of the camera and to
S132
M.-r. Chen et al. / Nuclear Instruments and Methods in Physics Research A 637 (2011) S130–S133
Fig. 6. Images of the resolution test. (a) 7 LP/mm (squeezed), (b) 7 LP/mm (coherent), (c) 10 LP/mm (squeezed), and (d) 10 LP/mm (coherent).
optimize the optical system. If the lens has an index of refraction n and is surrounded by a medium of index n0 , the object and image distances are L and L0 , and the radius of the surface is R, respectively. Fig. 4 shows the relationship between a ray incident on the lens and the refracted rays that result. The ray is refracted by the surface and intersects the axis at point A, and it is directed toward point B, where it would intersect the optical axis if the ray was extended. By applying the formula relating the object and image distances for a complete lens system [14], we get: n0 n n0 n : ¼ R L0 L
ð7Þ
The magnification is given by:
b¼
nL0 : n0 L
ð8Þ
The spherical aberration, coma, and astigmatism can be eliminated at the aplanatic point of the single surface. We get: L¼
n0 þ n R n
L0 ¼
n0 þ n R: n0
ð9Þ
ð10Þ
By substituting Eqs. (9) and (10) into Eq. (8), the magnification is: n2 : ð11Þ n0 2 Thus, n = 1, and we get b ¼ n10 2 :The size of the CCD is decreased by n0 2 times, and signal-to-noise ratio is improved by n0 2 times at the same time. The length of the optical path is shortened and the structure is more compact when the hyper-hemispherical
b¼
submersed lens is used. Moreover, the optical signal from every direction may be collected, and the efficiency is also improved.
2.3. Image detecting and saving The imaging instrument consists of the CCD, an IEEE1394 card, and a laptop computer. The CCD camera contains 1600 1200 pixels, with an effective size of 4.4 4.4 mm. It is sensitive in the wavelength range of 190–1100 nm. Its lowest measurable signal is 0.4 nW/cm2, the saturation intensity is 0.3 uW/cm2, and the damage threshold is 50 W/cm2, so it must be used carefully. With the included FireWire cable, the camera is connected to the notebook PC’s connector. An external power supply may be required, so a special IEEE-1394 cable must be connected from the notebook to the in-line power supply cable. Next, the powered IEEE-1394 cable should be connected to the camera. The image of the collected interface is shown in Fig. 5. Before a camera can be used to collect data, appropriate files must be selected by clicking the button options and using the drop-down arrow. Next, a vertical and horizontal pixel scale value appropriate for our optical system and camera is entered. The Pixel Units value that applies to the entered value is then selected. Because the camera is fitted with a lens, the Gamma setting should also be checked. In order to have this camera selected for subsequent sessions, the setup configuration should be saved. The collection of data from the camera begins when the ‘‘Start’’ menu item is clicked. Data frames can be saved or appended in the frame buffer. The image is exported with a BMP format. The test board is widely used to evaluate imaging systems and magnification techniques. The sector test board is 0.41, and it consists of various lead thicknesses. Lead thicknesses are limited
M.-r. Chen et al. / Nuclear Instruments and Methods in Physics Research A 637 (2011) S130–S133
by the resolution, with a maximum thickness of 0.03 mm for the board. Each test board is enclosed in plastic. The resolution range for our board is 1.5–20 LP/mm. The limiting resolution is determined by inspecting the finished graph. The experiment is conducted in a dark environment to decrease the influence of background light. Although the background light cannot be absolutely eliminated, the source is mainly non-classical light. The pinhole diaphragm is used as baffles to reduce scattered light. The positive lens (with f-number= 20 cm) may also be used to focus a collimated beam. To enable accurate adjustment of the resolution board and the CCD camera, both are located on the miniature linear stages that provide the XYZ configurations. The active imaging system with non-classical light is available. The resolution test experiment is used to test the feasibility of our scheme. The test is conducted with infrared squeezed light and infrared coherent light, respectively. As illustrated in Fig. 6(a) and (b), both images can be resolved when the LP number is 7 LP/mm. As shown in Fig. 6(c) and (d), the image formed by the nonclassical light can just be seen, while the image formed by the coherent infrared source cannot be distinguished when the LP number is increased to 10 LP/mm. The experimental results indicate that the resolution of active imaging with the infrared squeezed light is 1.43 times that of the infrared coherent light.
3. Conclusions The non-classical light is produced by crystal KTiOPO4 by using the OPO cavity. The active imaging technology with non-classical light has been studied. The results presented here confirm that
S133
the imaging system is available. Moreover, the resolution of the system with the non-classical light is about 1.43 times that of the infrared coherent light. The designed active imaging system based on non-classical light can meet the requirements of highresolution detection. High-resolution imaging with multimode quantum light that eliminates the effect of background light will be actively studied in the near future.
Acknowledgments This work was supported by the Knowledge Innovation Project and the Frontiers Discipline Arrangement Project, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, under Grant NO. 0654311213. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
V. Aebi, P. Vallianos, Laser Focus World 36 (9) (2000) 147. P.H. Merritt, M.A. Kramer, Proc. SPIE 3086 (1997) 2. B.L. Ulich, et al., Proc. SPIE 3059 (1997) 95. M.I. Kolobov, Rev. Mod. Phys. 71 (5) (1999) 1539. L.A. Lugiato, J. Opt. Soc. Am. B 14 (1997) 225. M. Martinelli, et al., Phys. Rev. A 67 (2) (2003) 023808. D. Sotler, Phys. Rev. D. 1 (12) (1970) 3217. M.I. Kolobov, C. Fabre, Phys. Rev. Lett. 85 (2000) 3789. A. Furusawa, et al., Science 282 (706) (1998). N.C. Menicucci, et al., Phys. Rev. Lett. 97 (11) (2006) 110501. I. Sokolov, M.I. Kolobov, A. Gatti, L.A. Lugiato, Opt. Commun. 193 (2001) 175. H.L. Ma, D. Wei, C.G. Ye, et al., Acta Phys. Sin. 54 (8) (2005) 3637. C. Gerry, et al., Introductory Quantum Optics, Vol. 1, Cambridge University Press, 2005. [14] Y.Y. An, X.D. Zeng, Principle of Photoelectron Detection, Pub House of Xidian University, 2004.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Study of non-classical light imaging technology Ming-rui Chen a,b,, Si-wen Bi a, Xi-bo Dou a,b, Wang-yun Liu a a b
State Key Laboratory of Transient Optics and Photonics, Chinese Academy of Sciences, Xi’an, 710119, China Graduate University of Chinese Academy of Sciences, Beijing, 100049, China
a r t i c l e in f o
a b s t r a c t
Available online 10 February 2010
Non-classical light that generates through the optical parametric down-conversion process by using an optical parametric oscillator is introduced, and the imaging system based on the light is built. The characteristics of the light and the spatial resolution of the image are studied. The light irradiates directly on the object plate, producing a mass of signal photons, then the signal photons are collected by the charge-coupled device. The output electrical signal is collected by a high-speed data collection card and processed with software. Finally, the object image is acquired, and its revised image is obtained by image processing. The results indicate that the resolution of the image based on the non-classical infrared light is 1.43 times that of infrared coherent light. The non-classical light can be widely used for high-resolution imaging, spectrum analysis, and micro-biological sample detection. & 2010 Elsevier B.V. All rights reserved.
Keywords: Imaging technology Non-classical light High-resolution Parametric down-conversion
1. Introduction In the last few years, there has been an increased interest in high-resolution and high signal-to-noise ratio imaging technology. Photoelectric imaging detection systems [1], such as surveillance, search, capture, and tracking, function as passive imaging detection. The passive imaging systems do not work well when the reflected signal energy is very weak. The shortcomings may be overcome by using an artificial optical radiation source [2,3]. However, the resolution of the imaging system cannot be improved continually because of the influence of the classical diffraction limit and quantum noise limit. From a quantum point of view, they must be described by a quantum state that spans over as many transverse modes as pixels [4]. Most quantum imaging ideas and experiments aim to generate the non-classical states of light that are needed in imaging [5,6]. Squeezed light is an important non-classical light that can overcome the laser shotnoise and quantum noise [7]. Recent proposals include the use of squeezed light beams. These beams display a quantum noise reduction in several portions of the transverse section in order to increase the resolution of image detection [8]. Additionally, squeezed light beams offer the possibility of quantum teleportation [9] or, in general, quantum computation [10] and parallel teleportation of quantum information by using either local squeezing or local entanglement [11].
Corresponding author at: State Key Laboratory of Transient Optics and Photonics, Chinese Academy of Sciences, Xi’an, 710119, China. Fax: + 86 29 88887603. E-mail address: [email protected] (M.-r. Chen).
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.02.039
An ideal candidate for generating squeezed light is parametric down-conversion by utilizing a nonlinear crystal, such as the periodically poled KTiOPO4, LiNbO3, KNbO3, and so forth [12]. The phase difference caused by diffraction is compensated by a nonlinear optical coefficient, and the walk-off effect of the crystal is also suppressed. Moreover, the KTiOPO4 crystal, with a larger spectral bandwidth and high transform coefficient, may be used at room temperature. The paper focuses on active imaging technology with nonclassical light. The generation of the light source, structure of the imaging system, working principle, and spatial resolution are also introduced. A target object image of non-classical light is acquired, and its revised image is obtained by image processing. The spatial resolution of this system can reach 10 LP/mm, as tested with a resolution board. The system can be widely used for very faint luminescence detecting, biological luminescence, and weak light detection.
2. Experiment setup A schematic of the imaging system is shown in Fig. 1. The system consists of a laser, a series of non-classical generating equipment, a double glue lens, a hyper-hemispherical submersed lens, a charge-coupled device (CCD), and a laptop computer. The output of the laser is fed into a pumped parametric oscillator (OPO), which provides the near infrared. The light irradiates directly on the object plate, producing a mass of signal photons, then the signal photons are collected by the CCD. The output electrical signal is collected by a high-speed data collection card
M.-r. Chen et al. / Nuclear Instruments and Methods in Physics Research A 637 (2011) S130–S133
S131
OPO Laser
Signal collected&processed
OPO
R2 Object Lens
CCD
H 4 FR
PC
H5
f4
M1
M2
Nd:YAG Laser
Fig. 1. Imaging system with squeezed light.
f1
H1
f2
f3
H 2 P2 H 3
P1
FP
Nonlinear crystal bˆ p
aˆi
aˆs
R1
Fig. 3. System of squeezed light.
Fig. 2. Generation of squeezed light.
and processed with software. Finally, the object image is acquired, and its revised image is obtained by image processing.
O
n’ R
2.1. Non-classical light source Fig. 2 shows the generation of squeezed light. A parametric down-converter essentially consists of two modes, usually called the signal mode and idler mode, coupled through a nonlinear crystal with a w(2) coefficient [13]. Here, a^ and b^ are the annihilation operators for the signal and pump modes, respectively. The Hamiltonian for degenerate parametric down-conversion is: ^ ^ ¼ ‘ oa^ þ a^ þ ‘ op b^ þ b^ þ i‘ wð2Þ ða^ 2 b^ þ a^ þ 2 bÞ: H
n B A
L’ L Fig. 4. Photoelectron detection with a hyper-hemispherical lens.
ð1Þ
In the parametric approximation, the pump field is treated classically, and the pump depletion is neglected. We assume that þ b^ and b^ are beiwp t and b eiwp t , respectively. The Hamiltonian in Eq. (1) becomes: ^ ðPAÞ ¼ ‘ oa^ þ a^ þ i‘ ðZ a^ 2 eiwp t Za^ þ 2 eiwp t Þ H
ð2Þ
(2)
where Z = w b. The Hamiltonian for the degenerate parametric down-converter, in the interaction picture, is: ^ I ðtÞ ¼ i‘ ½Z a^ 2 eiðop 2oÞt Za^ þ 2 eiðop 2oÞt : H
ð3Þ
Fig. 5. Data-collected software.
When the pump and signal frequencies satisfy op = 2o, we have: ^ I ¼ i‘ ðZ a^ 2 Za^ þ 2 Þ: H
ð4Þ
We then obtain: ^ I t=‘ Þ ¼ expðZ t a^ 2 Zt a^ þ 2 Þ: U^ I ðt; 0Þ ¼ expðiH Assuming that x = 2Zt, we can write: 1 1 ^ xÞ: x a^ 2 xa^ þ 2 ¼ Sð U^ I ðt; 0Þ ¼ exp 2 2
ð5Þ
ð6Þ
It is clear from Eq. (6) that squeezing is presented in the nonlinear optical processes. The laser is an amplified Nd:YAG continuous wave, single frequency system (INNOLIGHT DIABOLO) that delivers a beam at 1064 nm with 400 mW of average power and a beam at 532 nm with 800 mW of average power. The frequency stability is less than 2 MHz/min, and the long-term stability of the beam is less than 70.5%, respectively. The power of the light is controlled by optical equipment that consists of a half wave plate and a beam splitter. The infrared and the green light are fed into a synchronously pumped parametric oscillator that provides a signal beam at 1064 nm with 20 uW of average power and an
idler beam near 532 nm (not used). A schematic of the experiment setup is shown in Fig. 3. The curvature radius of the input mirror, M1, is 30 mm; the reflection of infrared light is 99.5%; and the transmission of green light is about 70%. The plane has a high transmission with both beams. The curvature radius of the output mirror, M2, is also 30 mm; the transmission of infrared light is 13.5%; and the reflection of green light is about 90%. The plane has a high transmission with infrared light. The size of the periodically polarized KTiOPO4 is l 2 12 mm. A piezoelectric transducer (PZT) is attached to mirror M1 for scanning of the cavity length. The distortion of the PZT can be utilized in the frequency stabilizing of the OPO cavity to keep the center of its resonant frequency unchanged.
2.2. Characteristics of the hyper-hemispherical submersed lens The hyper-hemispherical submersed lens in front of the CCD is used to improve the signal-to-noise ratio of the camera and to
S132
M.-r. Chen et al. / Nuclear Instruments and Methods in Physics Research A 637 (2011) S130–S133
Fig. 6. Images of the resolution test. (a) 7 LP/mm (squeezed), (b) 7 LP/mm (coherent), (c) 10 LP/mm (squeezed), and (d) 10 LP/mm (coherent).
optimize the optical system. If the lens has an index of refraction n and is surrounded by a medium of index n0 , the object and image distances are L and L0 , and the radius of the surface is R, respectively. Fig. 4 shows the relationship between a ray incident on the lens and the refracted rays that result. The ray is refracted by the surface and intersects the axis at point A, and it is directed toward point B, where it would intersect the optical axis if the ray was extended. By applying the formula relating the object and image distances for a complete lens system [14], we get: n0 n n0 n : ¼ R L0 L
ð7Þ
The magnification is given by:
b¼
nL0 : n0 L
ð8Þ
The spherical aberration, coma, and astigmatism can be eliminated at the aplanatic point of the single surface. We get: L¼
n0 þ n R n
L0 ¼
n0 þ n R: n0
ð9Þ
ð10Þ
By substituting Eqs. (9) and (10) into Eq. (8), the magnification is: n2 : ð11Þ n0 2 Thus, n = 1, and we get b ¼ n10 2 :The size of the CCD is decreased by n0 2 times, and signal-to-noise ratio is improved by n0 2 times at the same time. The length of the optical path is shortened and the structure is more compact when the hyper-hemispherical
b¼
submersed lens is used. Moreover, the optical signal from every direction may be collected, and the efficiency is also improved.
2.3. Image detecting and saving The imaging instrument consists of the CCD, an IEEE1394 card, and a laptop computer. The CCD camera contains 1600 1200 pixels, with an effective size of 4.4 4.4 mm. It is sensitive in the wavelength range of 190–1100 nm. Its lowest measurable signal is 0.4 nW/cm2, the saturation intensity is 0.3 uW/cm2, and the damage threshold is 50 W/cm2, so it must be used carefully. With the included FireWire cable, the camera is connected to the notebook PC’s connector. An external power supply may be required, so a special IEEE-1394 cable must be connected from the notebook to the in-line power supply cable. Next, the powered IEEE-1394 cable should be connected to the camera. The image of the collected interface is shown in Fig. 5. Before a camera can be used to collect data, appropriate files must be selected by clicking the button options and using the drop-down arrow. Next, a vertical and horizontal pixel scale value appropriate for our optical system and camera is entered. The Pixel Units value that applies to the entered value is then selected. Because the camera is fitted with a lens, the Gamma setting should also be checked. In order to have this camera selected for subsequent sessions, the setup configuration should be saved. The collection of data from the camera begins when the ‘‘Start’’ menu item is clicked. Data frames can be saved or appended in the frame buffer. The image is exported with a BMP format. The test board is widely used to evaluate imaging systems and magnification techniques. The sector test board is 0.41, and it consists of various lead thicknesses. Lead thicknesses are limited
M.-r. Chen et al. / Nuclear Instruments and Methods in Physics Research A 637 (2011) S130–S133
by the resolution, with a maximum thickness of 0.03 mm for the board. Each test board is enclosed in plastic. The resolution range for our board is 1.5–20 LP/mm. The limiting resolution is determined by inspecting the finished graph. The experiment is conducted in a dark environment to decrease the influence of background light. Although the background light cannot be absolutely eliminated, the source is mainly non-classical light. The pinhole diaphragm is used as baffles to reduce scattered light. The positive lens (with f-number= 20 cm) may also be used to focus a collimated beam. To enable accurate adjustment of the resolution board and the CCD camera, both are located on the miniature linear stages that provide the XYZ configurations. The active imaging system with non-classical light is available. The resolution test experiment is used to test the feasibility of our scheme. The test is conducted with infrared squeezed light and infrared coherent light, respectively. As illustrated in Fig. 6(a) and (b), both images can be resolved when the LP number is 7 LP/mm. As shown in Fig. 6(c) and (d), the image formed by the nonclassical light can just be seen, while the image formed by the coherent infrared source cannot be distinguished when the LP number is increased to 10 LP/mm. The experimental results indicate that the resolution of active imaging with the infrared squeezed light is 1.43 times that of the infrared coherent light.
3. Conclusions The non-classical light is produced by crystal KTiOPO4 by using the OPO cavity. The active imaging technology with non-classical light has been studied. The results presented here confirm that
S133
the imaging system is available. Moreover, the resolution of the system with the non-classical light is about 1.43 times that of the infrared coherent light. The designed active imaging system based on non-classical light can meet the requirements of highresolution detection. High-resolution imaging with multimode quantum light that eliminates the effect of background light will be actively studied in the near future.
Acknowledgments This work was supported by the Knowledge Innovation Project and the Frontiers Discipline Arrangement Project, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, under Grant NO. 0654311213. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
V. Aebi, P. Vallianos, Laser Focus World 36 (9) (2000) 147. P.H. Merritt, M.A. Kramer, Proc. SPIE 3086 (1997) 2. B.L. Ulich, et al., Proc. SPIE 3059 (1997) 95. M.I. Kolobov, Rev. Mod. Phys. 71 (5) (1999) 1539. L.A. Lugiato, J. Opt. Soc. Am. B 14 (1997) 225. M. Martinelli, et al., Phys. Rev. A 67 (2) (2003) 023808. D. Sotler, Phys. Rev. D. 1 (12) (1970) 3217. M.I. Kolobov, C. Fabre, Phys. Rev. Lett. 85 (2000) 3789. A. Furusawa, et al., Science 282 (706) (1998). N.C. Menicucci, et al., Phys. Rev. Lett. 97 (11) (2006) 110501. I. Sokolov, M.I. Kolobov, A. Gatti, L.A. Lugiato, Opt. Commun. 193 (2001) 175. H.L. Ma, D. Wei, C.G. Ye, et al., Acta Phys. Sin. 54 (8) (2005) 3637. C. Gerry, et al., Introductory Quantum Optics, Vol. 1, Cambridge University Press, 2005. [14] Y.Y. An, X.D. Zeng, Principle of Photoelectron Detection, Pub House of Xidian University, 2004.