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Continuous Wave THz Imaging System Based on Glow Discharge Detector

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Continuous Wave THz Imaging System Based on Glow Discharge Detector Powered By Docstoc
					                                            Continuous Wave THz Imaging System Based on Glow Discharge Detector
                                                                                    Lei Hou, Hongkyu Park and X.-C. Zhang
                                                                                     Research                         Institute Troy NY,
                                                                Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, NY 12180

                                        Introduction                                                                                             Challenges in THz Imaging                                                                     Glow Discharge Detector
A Glow discharge detector (GDD), based on a                                                                                        To use THz imaging for Real-life applications                                                      A GDD is a commercial neon lamp filled with low
commercial neon lamp, was used in a continuous wave                                                                                - THz source: efficiency and compactness                                                           pressure inert gases with Penning mixture and
(CW) terahertz (THz) imaging system. The                                                                                           -THz detector: response speed, sensitivity, operating                                              typically coated with phosphor. Two electrodes are
resp nsivity and n ise equivalent p wer (NEP) of a
responsivity      noise             power          f                                                                                               temperature, peratin
                                                                                                                                                   temperature operating spectrum and                                                                             lamp,     ionize
                                                                                                                                                                                                                                      placed parallel within the lamp which i nize the inert
GDD are 70 V/W and 1.26 × 10-6 W/Hz1/2,                                                                                                            cost effectiveness                                                                 gases, resulting in discharge current. The incident
respectively. The performance of the GDD can be                                                                                                                                                                                       THz wave enhances ionizing collisions of electrons
improved as commercial neon lamps do not have an                                                                                           THz                 NEP                        Response                                    with neutral atoms and causes an increase in the
                                                                                                                                                                                                               Price
optimized structure as a THz detector. The                                                                                               Detector            (W/Hz-1/2)                    speed                                      discharge current.
preliminary results indicate that a well-designed GDD                                                                               Schottky diode 10-10 ~ 10-12                              ~ kHz        expensive                             Low cost (less than $1)
will be an excellent THz detector with microsecond                                                                                                                                                                                               Electronic ruggedness
response time, wide spectral range (0.1 ~ 10 THz),
    p         ,        p           g (               ),                                                                              Pyroelectric           10-11 ~ 10-12                 < 100 Hz         expensive                             Broad spectral range (MW, IR, UV)
                                                                                                                                                                                                                                                        p           g (   , ,     )
high responsivity (> 1000 V/W) and low NEP (< 10-12                                                                                                                                                                                              Room-temperature operation
W/Hz1/2).                                                                                                                                Golay cell         10-11 ~ 10-12                 ~ 20 Hz          expensive                             Fast response speed (microsecond rise time)



                           CW THz Imaging System                                                                                           Responsivity and NEP of GDD                                                                          THz Images (0.2 THz)
                                                                                               68                                    subnormal       normal abnormal
                                                                                                                                                                                   -100
                                                                                                                                                                                                                  discharge current
                                                                                                                                       golw           golw   golw
                                                                                                                                                                                                                      a: 3.0 mA
                                                                                                                                                                                               a
                                                                          U (V)




                                                                                               66                                                                                                                     b: 5.3 mA




                                                                                                                                                                         /Hz)
                                                                                                                                                                                   -110                               c: 6.7 mA
                                                                                                                                                                                                                      d: 8.1 mA




                                                                                                                                                                              rms
                                                                                                                                                                                               b                      e: 10.2 mA




                                                                                                                                                                         2
                                                                                                                                                                         Sv (dbV
                                                                                               64                                                                                              c
                                                                                                                                                                                   -120
                                                                                                                                                                                               d
                                                                                 ivity (V/W)




                                                                                                                                                                                               e
                                                                                               60
                                                                                                                                                                                   -130
                                                                                                                                                                                          0        20      40     60      80      100            Fi st Aid Kit
                                                                                                                                                                                                                                                 First               THz i
                                                                                                                                                                                                                                                                     TH image by GDD
                                                                                                                                                                                                                                                                              b
                                                                          responsi




                                                                                               40                                                                                                       frequency (kHz)
 Schematic diagram of the 0.2 THz imaging                                                                                                                                                           Noise spectrum
                                                                                               20
 system based on GDD.                                                                                0                               2      4      6        8      10
                                                                                                                                          current (mA)                                             noise power spectral density
                          20                                                                                                                                                        NEP =
                                            modulation signal                                  Amplified responsivity (Gain: 130)                                                                         responsivi ty
                                            THz signal
     THz amplitude (mV)




                          10                                                                                                                                                                  = 1.26 × 10 − 6 W / Hz
                                                                                                         amplitud (a.u.)




                                                                                                                           6
                                                                                               300
                                                                                                                                                                                     when
                 e




                                                                                                                           4
                                                                                                                de




                                                                                                                           2
                           0                                                                                               0                                                         :discharge current of GDD is 8.8 mA                     PC Board            GDD         Schottky diode
                                                                                                                                                                                     :chopping frequency is 900 Hz
                                                                         α (1/cm)




                                                                                               200                             0     1     2     3
                                                                                                                                     f (THz)

                          -10
                                                                                                                                                                                     Deficient NEP caused by:
                                                                                               100
                                                                                                                                                                                                                                                            References
                          -20                                                                                                                                                             Absorption of glass wall
                                0   1     2     3      4        5                                                                                                                                                                          1. A. Abramovich, N. S. Kopeika, D. Rozban and E.
                                         time (ms)
                                                                                                0
                                                                                                                               0.5       1.0    1.5   2.0   2.5    3.0                    Scattering of glass wall                            Farber, Appl. Opt. 46, 7207-7211 (2007).
 0.2 THz signal measured from the GDD by an                                                                                               freqnency (THz)                                 Mi       h between TH b
                                                                                                                                                                                          Mismatch b          THz beam                     2. D. Rozban, N. S. Kopeika, A. Abramovich, and E.
 oscilloscope. Chopping frequency : 900 Hz.                                               Absorption coefficient of glass wall                                                            size and gap size of GDD                            Farber, J. Appl. Phys. 103, 093306 (2008).

                          This material is based upon work supported by the U.S. Department of Homeland Security under Award Number 2008-ST-061-ED0001. The views and conclusions contained in this document
                          are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied of the U.S. Department of Homeland Security.

				
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