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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 3 — Jan. 30, 2012
  • pp: 2772–2778
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Stand-alone system for high-resolution, real-time terahertz imaging

Maria I. Amanti, Giacomo Scalari, Mattias Beck, and Jerome Faist  »View Author Affiliations


Optics Express, Vol. 20, Issue 3, pp. 2772-2778 (2012)
http://dx.doi.org/10.1364/OE.20.002772


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Abstract

In this work we present a stand-alone, portable system for high resolution real-time THz imaging. The total weight of the apparatus is less than 15 kg and its physical dimension is of ~(65 cm)3. A quantum cascade laser emitting at 3.4 THz laser based on a third-order distributed feedback cavity is used as source. It operates in continuous-wave at 50 K with more than 1 mW output power and less than 300 mW of power consumption. High resolution real-time THz imaging is reported: resolution of 2.5 times the wavelength is demonstrated.

© 2012 OSA

1. Introduction

THz imaging systems are interesting both for research and commercial applications. For instance the unique transitions of molecules in THz range, due to rotational and vibration levels, can be exploited to study specific functions of the samples or as fingerprint for security reasons [1

1. H. Zhong, A. Redo-Sanchez, and X.-C. Zhang, “Identification and classification of chemicals using terahertz reflective spectroscopic focal-plane imaging system,” Opt. Express 14(20), 9130–9141 (2006). [CrossRef] [PubMed]

4

4. Y. C. Shen, T. Lo, P. F. Taday, B. E. Cole, R. Tribe, and M. C. Kemp, “Detection and identification of explosives using terahertz pulsed spectroscopic imaging,” Appl. Phys. Lett. 86(24), 241116 (2005). [CrossRef]

]. Moreover, thanks to the low photon energies, the use of THz radiation in biomedical applications could prevent the screening exposure of biological tissues to harmful radiations such as x-rays [5

5. S. M. Kim, F. Hatami, J. S. Harris, A. W. Kurian, J. Ford, D. King, G. Scalari, M. Giovannini, N. Hoyler, J. Faist, and G. Harris, “Biomedical terahertz imaging with a quantum cascade laser,” Appl. Phys. Lett. 88(15), 153903 (2006). [CrossRef]

,6

6. R. M. Woodward, V. P. Wallace, D. D. Arnone, E. H. Linfield, and M. Pepper, “Terahertz pulsed imaging of skin cancer in the time and frequency domain,” J. Biol. Phys. 29(2/3), 257–259 (2003). [CrossRef]

]. The good transparency to the THz radiation of non-metallic materials, such as plastics, ceramics and polymers and the high penetration depth, makes this radiation valuable for applications as non-destructive material quality control and homeland security [3

3. K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express 11(20), 2549–2554 (2003). [CrossRef] [PubMed]

,7

7. N. Karpowicz, H. Zhong, C. Zhang, K.-I. Lin, J.-S. Hwang, and X. C. Zhang, “Depth-resolving THz imaging with tomosynthesis,” Opt. Express 17, 9558–9570 (2009). [CrossRef]

9

9. D. Mittleman, Sensing with Terahertz Radiation (Springer Series in Optical Sciences, vol. 85 2003).

].

The main requirements for THz systems in most of the applications are high resolution images and fast detection. In addition, in order to be able to bring the THz imaging out of the laboratory environment, compactness and portability of the measurements apparatus are key elements. In this work we will show that it is possible to combine these properties, presenting a stand-alone system of less than 15 kg of weight, which can achieve a resolution of 200 µm (2.2 times the wavelength) for real time acquisition.

Among the different realizations of THz imaging systems two basic principles can be distinguished: either ultra-short pulses are used to generate a broadband THz radiation or sharp continuous-wave sources are employed [10

10. A. M. Sinyukov, Z. Liu, Y. L. Hor, K. Su, R. B. Barat, D. E. Gary, Z.-H. Michalopoulou, I. Zorych, J. F. Federici, and D. Zimdars, “Rapid-phase modulation of terahertz radiation for high-speed terahertz imaging and spectroscopy,” Opt. Lett. 33(14), 1593–1595 (2008). [CrossRef] [PubMed]

].

In the first case coherent imaging is achieved by raster scanning a sample trough the focus of the THz beam and full spectroscopic information is recorded for each pixel. However this approach is far to be compact and it is inherently slow: few minutes are needed to acquire an image of 400x400 pixels in the fastest systems [10

10. A. M. Sinyukov, Z. Liu, Y. L. Hor, K. Su, R. B. Barat, D. E. Gary, Z.-H. Michalopoulou, I. Zorych, J. F. Federici, and D. Zimdars, “Rapid-phase modulation of terahertz radiation for high-speed terahertz imaging and spectroscopy,” Opt. Lett. 33(14), 1593–1595 (2008). [CrossRef] [PubMed]

]. On the other side, thanks to optimized optical schemes based on the confocal principle, spatial resolution of ~2λ has been demonstrated for these systems [11

11. N. N. Zinov’ev and A. V. Andrianov, “Confocal terahertz imaging,” Appl. Phys. Lett. 95(1), 011114 (2009). [CrossRef]

]; values close to λ have been reported with quasi-near-field techniques [12

12. X. Wang, Y. Cui, D. Hu, W. Sun, J. Ye, and Y. Zhang, “Terahertz quasi-near-field real time imaging,” Opt. Commun. 282(24), 4683–4687 (2009). [CrossRef]

]. To overcome the speed limitation of the measurement apparatus based on ultra-short pulses, promising results have been reported using a compressing sensing scheme [13

13. W. L. Chan, K. Charan, D. Takhar, K. F. Kelly, R. G. Baraniuk, and D. M. Mittleman, “A single-pixel terahertz imaging system based on compressed sensing,” Appl. Phys. Lett. 93(12), 121105 (2008). [CrossRef]

], where random acquisition and special reconstruction routines can reduce the acquisition time of the 70%; however this is still far from a real time measurement.

To achieve real time operation and frequency-sensitive measurements, imaging systems based on continuous wave sources and an incoherent system of detection, as micro-bolometer arrays, have been developed. The possible sources of radiation available are solid-state frequency multipliers at sub-millimeter-wave frequencies, far-infrared gas laser, two colors external-cavity lasers [14

14. M. Scheller, J. M. Yarborough, J. V. Moloney, M. Fallahi, M. Koch, and S. W. Koch, “Room temperature continuous wave milliwatt terahertz source,” Opt. Express 18(26), 27112–27117 (2010). [CrossRef] [PubMed]

] or quantum cascade lasers (QCL). Because of their compact size, QCLs are one of the most attractive sources. However, these lasers are generally limited in performance in terms of combination of low power consumption, beam quality, spectral control and output optical power, limiting their use in compact systems for THz imaging. Good results for real time imaging using QCLs have been reported in references [15

15. A. W. M. Lee, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Real-time imaging using a 4.1-THz quantum cascade laser and a 320 X 240 microbolometer focal-plane array,” IEEE Photon. Technol. Lett. 18(13), 1415–1417 (2006). [CrossRef]

,16

16. B. N. Behnken, G. Karunasiri, D. R. Chamberlin, P. R. Robrish, and J. Faist, “Real-time imaging using a 2.8 THz quantum cascade laser and uncooled infrared microbolometer camera,” Opt. Lett. 33(5), 440–442 (2008). [CrossRef] [PubMed]

] and in reference [17

17. A. W. M. Lee, Q. Qin, S. Kumar, B. S. Williams, Q. Hu, and J. L. Reno, “Real time terahertz imaging over a standoff distance (> 25 meters),” Appl. Phys. Lett. 89(14), 141125 (2006). [CrossRef]

] over long distance (> 25 m), but the highest resolution reported is 7.2 λ [15

15. A. W. M. Lee, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Real-time imaging using a 4.1-THz quantum cascade laser and a 320 X 240 microbolometer focal-plane array,” IEEE Photon. Technol. Lett. 18(13), 1415–1417 (2006). [CrossRef]

] and the systems were not optimized for portability. Promising results based on raster scanning acquisition and QCLs have been demonstrated for compact apparatus in reference [18

18. H. Richter, M. Greiner-Bär, S. G. Pavlov, A. D. Semenov, M. Wienold, L. Schrottke, M. Giehler, R. Hey, H. T. Grahn, and H. W. Hübers, “A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler,” Opt. Express 18(10), 10177–10187 (2010). [CrossRef] [PubMed]

] and for dual-frequency imaging in reference [19

19. P. Dean, N. K. Saat, S. P. Khanna, M. Salih, A. Burnett, J. Cunningham, E. H. Linfield, and A. G. Davies, “Dual-frequency imaging using an electrically tunable terahertz quantum cascade laser,” Opt. Express 17(23), 20631–20641 (2009). [CrossRef] [PubMed]

].

In this work we present the successful implementation of a stand-alone set-up for real-time THz imaging using as source a THz QCL emitting at 3.4 THz [20

20. M. I. Amanti, G. Scalari, R. Terazzi, M. Fischer, M. Beck, J. Faist, A. Rudra, P. Gallo, and E. Kapon, “Bound-to-continuum terahertz quantum cascade laser with a single quantum well phonon extraction/injection stage,” New J. Phys. 11(12), 125022 (2009). [CrossRef]

], based on a third order distributed-feedback cavity [21

21. M. I. Amanti, M. Fischer, G. Scalari, M. Beck, and J. Faist, “Low-divergence single-mode terahertz quantum cascade laser,” Nat. Photonics 3(10), 586–590 (2009). [CrossRef]

]. Thanks to this laser geometry, improved performance of the laser are obtained; we demonstrate high resolution imaging using a single lens with a high numerical aperture and a single frame acquisition. Images and movies of imaging in the THz of more extended sample but with lower resolution are also presented.

2. Experimental set up and laser source

Experimental set-up

The THz imaging system presented in this work includes as source a THz QCL operating in a thermo-mechanical cryo-cooler (Sunpower, CryoteTel CT) at a temperature of 50K and a duty cycle of 50%. The detector is a commercial available un-cooled micro-bolometer camera (INO, IRXCAM) with 160 x 120 elements (pixel pitch is 52 µm), optimized for operation at 3 THz. The Noise equivalent power of the system is evaluated by the manufacturer in Ref [22

22. M. Bolduc, M. Terroux, B. Tremblay, L. Marchese, E. Savard, M. Doucet, H. Oulachgar, C. Alain, H. Jerominek, and A. Bergeron, “Noise-equivalent power characterization of an uncooled microbolometer-based THz imaging camera” Proc. of SPIE, 8023, art. no 80230C, 201, 2011.

] to a value ~80 pW using an high-resistive Si objective with f/0.95. The single frame used in the measurements is 0.033 seconds. The camera is connected to a computer laptop for the acquisition of the images; the laptop controls as well the cryo-cooler. The optical elements are diffractive and made in high-density polyethylene.

The electrical power dissipation of the entire system is around 265 W: 206 W for the cryo-cooler, 150 mW for the laser, 8 W for the camera and an average of 50 W for the computer. The total weight of all the elements is less than 15 kg: 5 kg for the cryo-cooler, 4.5 kg for the laser power supply, 1 kg for the cryo-cooler power supply, 0.5 kg for the camera and 0.05 kg for the optical elements. Moreover the physical dimensions of the elements are such that the entire system could be compacted in a parallelepiped of 70 cm x 60 cm x 60cm (See Fig. 1a
Fig. 1 Photos of the stand-alone system for THz imaging. a) Detailed vision of all the elements. b) Packed version operating in transmission mode
). In Fig. 1b is shown a packed version of the system, where the cryo-cooler and the power supplies are placed together.

The limited power consumption, the small weight load and the compactness of the THz imaging system presented in this work demonstrate its portability and its validity as stand-alone system.

Laser source

The laser source is a THz QCL emitting at 3.4 THz. The active region is based on a four well design with an extraction mechanism based on the emission of LO phonons [18

18. H. Richter, M. Greiner-Bär, S. G. Pavlov, A. D. Semenov, M. Wienold, L. Schrottke, M. Giehler, R. Hey, H. T. Grahn, and H. W. Hübers, “A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler,” Opt. Express 18(10), 10177–10187 (2010). [CrossRef] [PubMed]

]. The sample has been processed following standard double metal procedure and a third-order distributed feedback cavity has been engineered for it [21

21. M. I. Amanti, M. Fischer, G. Scalari, M. Beck, and J. Faist, “Low-divergence single-mode terahertz quantum cascade laser,” Nat. Photonics 3(10), 586–590 (2009). [CrossRef]

].

As shown in reference [23

23. M. I. Amanti, G. Scalari, F. Castellano, M. Beck, and J. Faist, “Low divergence Terahertz photonic-wire laser,” Opt. Express 18(6), 6390–6395 (2010). [CrossRef] [PubMed]

], thanks to this cavity design, it is possible to improve the out-coupling efficiency of the laser and to achieve good beam quality, high output optical power and spectral control of the laser emission. Moreover the device presented in this work has been processed in very narrow waveguides (15 µm wide, 800 µm long) in order to reduce the power consumption in the laser.

In Fig. 2a
Fig. 2 a) Measured optical power versus electrical power dissipation of the THz quantum cascade laser at different temperatures. Inset: measured frequency emission. b) Measured beam pattern of the laser. A FWHM of 22° X 30° for the laser emission is demonstrated
is reported the measured emitted optical power of the laser in continuous wave mode versus the dissipated power, for different temperatures. It is clear that this kind of devices have less stringent requirements for the cooling power needed for operation and compact cryo-cooler can be employed. It is also important to notice that there is almost no difference in the laser performance at 10 K and 50 K. The output optical power at high temperature, despite of the limited power consumption, is comparable to devices dissipating more power [24

24. B. S. Williams, S. Kumar, Q. Hu, and J. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13(9), 3331–3339 (2005). [CrossRef] [PubMed]

].

In Fig. 2b is reported the measured emission beam of the laser output any intermediate optical element. Despite of the subwavelength lateral dimensions of the device, thanks to the third order grating, a narrow beam of full-width-half-maximum of 22° x 30° is demonstrated.

3. Experimental results

The materials studied in this work are different kinds of plastics such as polyethylene, polypropylene and polystyrene. Similar results have been obtained for all these materials so in the following we show mainly the results for plastics opaque in the visible. These materials are extremely interesting due to their large use in very different applications. Polyethylene and high density polyethylene are used, for instance, for milk container, shampoo and detergent bottles, food container and dishware, water pipes; polypropylene is used for auto parts, soft drinks bottles, food container and dishware; polystyrene is used for disposable cups and plates, packing materials and CD cases.

We studied either the contrast given by the difference in thickness in the plastic itself or the contrast due to objects hidden in the plastic. All the images presented in the following have been obtained by single frame acquisition and real time movie are reported in the multimedia files Media 1, Media 2, Media 3, Media 4, and Media 5. Compared to the single frame images, real time acquisition takes advantage of the integration ability of the eye and the pattern recognition function of the brain, reaching a higher quality of the images.

We used two different schemes of the optical elements to perform THz imaging. The first one is for high resolution images: the sample is illuminated directly from the laser light and the image is collected from a single lens with short focal length (See Fig. 3
Fig. 3 Single-frame THz imaging of some shapes imprinted in different kinds of plastics (details presented in the first column of the figure). The real time imaging of the second row is reported in the file Media 1. The last row presents a characterization of the system resolution with 10 slits of varying widths cut out on a metal piece (widths are, from left to right: 1mm, 500 −370-280-210-160-120-90-70-50 µm). The three THz images are relative to the 1 mm and 0.5 mm, the 370-280-210-160 µm and the 160-120-90-70-50 µm. On the top: schematic of the experimental set-up
). The lens parameters are: focal length f = 30 mm and the diameter is d = 40 mm; the distance a between the object and the lens is 6 cm and the distance b between the lens and the camera is 6 cm. The numerical aperture (NA) of the system is 0.32 (sin(arctan(d/2/a))). The highest resolution achievable is then 220 µm, according to Abbe’s theory (0.82λ/NA). The experimental results are shown in Fig. 3, where the THz images of some shapes imprinted in different plastics are reported. Objects separated by distance of ~220 µm can be clearly resolved, attending the expected resolution. The illuminated area in this configuration is 3 mm x 6 mm. In this configuration the single frame signal-to-noise ratio of the system is 5 and is obtained by measuring the average value of the voltage readout of the individual pixel when the laser source is switched on and off.

A further characterization of the resolution achievable from the system has been performed by imaging a set of 10 slits of different widths (1mm, 500 −370-280-210-160-120-90-70-50 µm) cut out by laser machining on a metallic foil. As visible from Fig. 3, bottom row, we are able to see transmitted THz through all the slits and to resolve the size change down to to the 5th slit from the left, which has a width of 210 µm. This confirms our resolution claim for the setup in this configuration.

In the second configuration we used two lenses of focal length f = 30 mm and f1 = 95 cm (See Fig. 4
Fig. 4 First column: Images in the visible. Second and third columns: single-frame THz transmission images. First row: metallic blade in polystyrene. Second row: Lead pencil in polystyrene. Third row: Water droplets in high- density polyethylene bottle. Fourth row: writing “ETH” inside a DVD box. The real time imaging is in the multimedia: Media 2, Media 3, Media 4, and Media 5, respectively. On the top: schematic of the experimental set-up
). The object is placed in between the two lenses where a nearly parallel beam is expected. The image is then focused on the camera by the second lens. The illuminated area in this case is 1.1 cm x 1.4 cm. The experimental results are presented in Fig. 4. Good contrast is demonstrated for metallic object hidden in plastic but also for non-conducting small element as a pencil lead. Liquids in a bottle can also clearly be measured, presenting the potentiality of this system for the detection of different substances in container opaque in the visible. A writing cut out from standard paper has been concealed in a DVD box: transmitted signal through the two box surfaces allows to clearly distinguish the hidden writing “ETH”. Imaging of larger features imprinted in the plastic, compared to what shown in Fig. 3, is also demonstrated. These data is also presented as movies in the multimedia material section.

4. Conclusion

In conclusion we reported the successful demonstration of a stand-alone system for high resolution real-time THz imaging, with low power consumption and reduced physical dimension. A similar system could be adapted in the future for spectroscopic measurements and heterodyne receivers, opening the route toward a more diffuse use of THz quantum cascade laser as valid THz sources. We gratefully acknowledge financial support from NCCR “Quantum Photonics” and SNF through the project “Terascope” and the technical support from Alpes Lasers.

Acknowledgments

We would like to acknowledge Christopher Bonzon for help in the experiments. Moreover we acknowledge Lubos Hvozdara for helping in the early stage of the project.

References and links

1.

H. Zhong, A. Redo-Sanchez, and X.-C. Zhang, “Identification and classification of chemicals using terahertz reflective spectroscopic focal-plane imaging system,” Opt. Express 14(20), 9130–9141 (2006). [CrossRef] [PubMed]

2.

M. Walther, B. M. Fischer, A. Ortner, A. Bitzer, A. Thoman, and H. Helm, “Chemical sensing and imaging with pulsed terahertz radiation,” Anal. Bioanal. Chem. 397(3), 1009–1017 (2010). [CrossRef] [PubMed]

3.

K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express 11(20), 2549–2554 (2003). [CrossRef] [PubMed]

4.

Y. C. Shen, T. Lo, P. F. Taday, B. E. Cole, R. Tribe, and M. C. Kemp, “Detection and identification of explosives using terahertz pulsed spectroscopic imaging,” Appl. Phys. Lett. 86(24), 241116 (2005). [CrossRef]

5.

S. M. Kim, F. Hatami, J. S. Harris, A. W. Kurian, J. Ford, D. King, G. Scalari, M. Giovannini, N. Hoyler, J. Faist, and G. Harris, “Biomedical terahertz imaging with a quantum cascade laser,” Appl. Phys. Lett. 88(15), 153903 (2006). [CrossRef]

6.

R. M. Woodward, V. P. Wallace, D. D. Arnone, E. H. Linfield, and M. Pepper, “Terahertz pulsed imaging of skin cancer in the time and frequency domain,” J. Biol. Phys. 29(2/3), 257–259 (2003). [CrossRef]

7.

N. Karpowicz, H. Zhong, C. Zhang, K.-I. Lin, J.-S. Hwang, and X. C. Zhang, “Depth-resolving THz imaging with tomosynthesis,” Opt. Express 17, 9558–9570 (2009). [CrossRef]

8.

N. Karpowicz, H. Zhong, C. Zhang, K.-I. Lin, J.-S. Hwang, J. Xu, and X. C. Zhang, “Compact continuous-wave subterahertz system for inspection applications,” Appl. Phys. Lett. 86(5), 054105 (2005). [CrossRef]

9.

D. Mittleman, Sensing with Terahertz Radiation (Springer Series in Optical Sciences, vol. 85 2003).

10.

A. M. Sinyukov, Z. Liu, Y. L. Hor, K. Su, R. B. Barat, D. E. Gary, Z.-H. Michalopoulou, I. Zorych, J. F. Federici, and D. Zimdars, “Rapid-phase modulation of terahertz radiation for high-speed terahertz imaging and spectroscopy,” Opt. Lett. 33(14), 1593–1595 (2008). [CrossRef] [PubMed]

11.

N. N. Zinov’ev and A. V. Andrianov, “Confocal terahertz imaging,” Appl. Phys. Lett. 95(1), 011114 (2009). [CrossRef]

12.

X. Wang, Y. Cui, D. Hu, W. Sun, J. Ye, and Y. Zhang, “Terahertz quasi-near-field real time imaging,” Opt. Commun. 282(24), 4683–4687 (2009). [CrossRef]

13.

W. L. Chan, K. Charan, D. Takhar, K. F. Kelly, R. G. Baraniuk, and D. M. Mittleman, “A single-pixel terahertz imaging system based on compressed sensing,” Appl. Phys. Lett. 93(12), 121105 (2008). [CrossRef]

14.

M. Scheller, J. M. Yarborough, J. V. Moloney, M. Fallahi, M. Koch, and S. W. Koch, “Room temperature continuous wave milliwatt terahertz source,” Opt. Express 18(26), 27112–27117 (2010). [CrossRef] [PubMed]

15.

A. W. M. Lee, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Real-time imaging using a 4.1-THz quantum cascade laser and a 320 X 240 microbolometer focal-plane array,” IEEE Photon. Technol. Lett. 18(13), 1415–1417 (2006). [CrossRef]

16.

B. N. Behnken, G. Karunasiri, D. R. Chamberlin, P. R. Robrish, and J. Faist, “Real-time imaging using a 2.8 THz quantum cascade laser and uncooled infrared microbolometer camera,” Opt. Lett. 33(5), 440–442 (2008). [CrossRef] [PubMed]

17.

A. W. M. Lee, Q. Qin, S. Kumar, B. S. Williams, Q. Hu, and J. L. Reno, “Real time terahertz imaging over a standoff distance (> 25 meters),” Appl. Phys. Lett. 89(14), 141125 (2006). [CrossRef]

18.

H. Richter, M. Greiner-Bär, S. G. Pavlov, A. D. Semenov, M. Wienold, L. Schrottke, M. Giehler, R. Hey, H. T. Grahn, and H. W. Hübers, “A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler,” Opt. Express 18(10), 10177–10187 (2010). [CrossRef] [PubMed]

19.

P. Dean, N. K. Saat, S. P. Khanna, M. Salih, A. Burnett, J. Cunningham, E. H. Linfield, and A. G. Davies, “Dual-frequency imaging using an electrically tunable terahertz quantum cascade laser,” Opt. Express 17(23), 20631–20641 (2009). [CrossRef] [PubMed]

20.

M. I. Amanti, G. Scalari, R. Terazzi, M. Fischer, M. Beck, J. Faist, A. Rudra, P. Gallo, and E. Kapon, “Bound-to-continuum terahertz quantum cascade laser with a single quantum well phonon extraction/injection stage,” New J. Phys. 11(12), 125022 (2009). [CrossRef]

21.

M. I. Amanti, M. Fischer, G. Scalari, M. Beck, and J. Faist, “Low-divergence single-mode terahertz quantum cascade laser,” Nat. Photonics 3(10), 586–590 (2009). [CrossRef]

22.

M. Bolduc, M. Terroux, B. Tremblay, L. Marchese, E. Savard, M. Doucet, H. Oulachgar, C. Alain, H. Jerominek, and A. Bergeron, “Noise-equivalent power characterization of an uncooled microbolometer-based THz imaging camera” Proc. of SPIE, 8023, art. no 80230C, 201, 2011.

23.

M. I. Amanti, G. Scalari, F. Castellano, M. Beck, and J. Faist, “Low divergence Terahertz photonic-wire laser,” Opt. Express 18(6), 6390–6395 (2010). [CrossRef] [PubMed]

24.

B. S. Williams, S. Kumar, Q. Hu, and J. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13(9), 3331–3339 (2005). [CrossRef] [PubMed]

OCIS Codes
(140.5965) Lasers and laser optics : Semiconductor lasers, quantum cascade
(110.6795) Imaging systems : Terahertz imaging

ToC Category:
Imaging Systems

History
Original Manuscript: September 13, 2011
Revised Manuscript: December 9, 2011
Manuscript Accepted: January 2, 2012
Published: January 23, 2012

Citation
Maria I. Amanti, Giacomo Scalari, Mattias Beck, and Jerome Faist, "Stand-alone system for high-resolution, real-time terahertz imaging," Opt. Express 20, 2772-2778 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-3-2772


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References

  1. H. Zhong, A. Redo-Sanchez, and X.-C. Zhang, “Identification and classification of chemicals using terahertz reflective spectroscopic focal-plane imaging system,” Opt. Express14(20), 9130–9141 (2006). [CrossRef] [PubMed]
  2. M. Walther, B. M. Fischer, A. Ortner, A. Bitzer, A. Thoman, and H. Helm, “Chemical sensing and imaging with pulsed terahertz radiation,” Anal. Bioanal. Chem.397(3), 1009–1017 (2010). [CrossRef] [PubMed]
  3. K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express11(20), 2549–2554 (2003). [CrossRef] [PubMed]
  4. Y. C. Shen, T. Lo, P. F. Taday, B. E. Cole, R. Tribe, and M. C. Kemp, “Detection and identification of explosives using terahertz pulsed spectroscopic imaging,” Appl. Phys. Lett.86(24), 241116 (2005). [CrossRef]
  5. S. M. Kim, F. Hatami, J. S. Harris, A. W. Kurian, J. Ford, D. King, G. Scalari, M. Giovannini, N. Hoyler, J. Faist, and G. Harris, “Biomedical terahertz imaging with a quantum cascade laser,” Appl. Phys. Lett.88(15), 153903 (2006). [CrossRef]
  6. R. M. Woodward, V. P. Wallace, D. D. Arnone, E. H. Linfield, and M. Pepper, “Terahertz pulsed imaging of skin cancer in the time and frequency domain,” J. Biol. Phys.29(2/3), 257–259 (2003). [CrossRef]
  7. N. Karpowicz, H. Zhong, C. Zhang, K.-I. Lin, J.-S. Hwang, and X. C. Zhang, “Depth-resolving THz imaging with tomosynthesis,” Opt. Express17, 9558–9570 (2009). [CrossRef]
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