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University of Tokushima Osaka University
TST2012@Prague (2012.6.19)
Line-field terahertz computed tomography of continuously
rotating object T. Yasui,1,2 Y. Ohgi,1 M. Minami,1 M. Jewariya,2
M. Nagai,1 T. Araki,1 and E. Abraham3 1Grad. Sch. Engg. Sci, Osaka Univ., Japan
2Inst. Tech. Sci., Univ. Tokushima, Japan 3LOMA, Univ. Bordeaux, France
University of Tokushima Osaka University
X-ray Computed Tomography (X-ray CT)
Advantage: High penetration Disadvantages: Hazardous ionizing effect Too high penetration Monochrome image →Difficult to analyze chemical components
Utility: Nondestructive inspection Medical imaging
University of Tokushima Osaka University
THz CT THz radiation Moderate penetration in opaque soft materials, insensitivity to optical scattering, low photon energy, and good beam coherence Spectral images for material characterization
Ref) Ferguson, OL 27, 1312 (2002). Ref) Recur, OpEx 19, 5105 (2011). Optical photograph THz CT image
University of Tokushima Osaka University
Rapid THz color scanner equipped with real-time line scanning of THz beam
time-to-space conversion in EO srystal
Ref) Yasui, OpEx 16, 1208 (2008); Schirmer, Biomed. OpEx 1, 354 (2010) .
Line imaging of THz beam line-focused on sample
Ref) Shan, OL 25, 426 (2000)
University of Tokushima Osaka University
Present talk THz color line projection in real time without any mechanical scanning
Significant increase of image acquisition rate in THz CT
• Fast THz CT system based on real-time line projection of THz beam
• Apply it for continuously rotating sample
University of Tokushima Osaka University Experimental setup
Frame rate = 100 Hz
Ref) Jewariya, JOSA B 26, A101 (2009)
Record 600 projections line data during 6 sec while rotating the
sample continuously by 360 degree
Data acquisition condition
LN
(60 deg/sec)
THz temporal line projection
2D-ST THz image
FBP: filtered back-projection
University of Tokushima Osaka University
Time characteristics
Temporal line projection data (without sample)
Temporal waveform
0
10
20
0
100
200
0 100 200
Time [ps]
Horizontal coordinate [pixel]
Vertical coordinate [pixel]
Pos
ition
[mm
]
-9000 34000 0
Electric field [a.u.]
0 10 20 30
Temporal Waveform
0.38ps
DR Cherencov radiation in LN crystal
Opt. rectification in ZnTe crystal
945
100 fps
1000 100 10 1 Frame rate (Hz)
University of Tokushima Osaka University
Spectral characteristics
Spectral bandwidth = 3THz, Spectral resolution = 27GHz
Line projection data of spectral amplitude Comparison of
amplitude spectrum
University of Tokushima Osaka University
Result (1): Four metallic bars (φ=2 mm)
(d)
(a) (b)
(d)(c)
2 mm
2 mm
THz focal line
Sample photograph Sinogram
Reconstructed cross-section
Ep-p
Spectral Amp. at 0.6 THz
360 degree
20 m
m
Continuous rotating
(360degree@6sec)
Strong Weak Signal
University of Tokushima Osaka University
Result (2): Teflon cylinder (φ=10 mm) drilled with off-axis cylindrical hole (φ=2 mm)
Sample
Sinogram Reconstructed cross-section
Continuous rotating
(360degree@6sec)
hole
Strong Weak Signal
n=1.45, α=2cm-1
Ep-p
University of Tokushima Osaka University
Result (3): Powder sample (30% lactose and 70% PE) filled in off-axis hole of foam cylinder
Absorption spectrum of lactose powder
Sinogram Reconstructed cross-section
Spect. amp. at 0.53 THz
Strong Weak Signal
(b)(a)
4 mm
Sample Foam (n=1.15, α=0.1cm-1)
Powder sample
University of Tokushima Osaka University
Summary (1) THz CT equipped with real-time line
projection at a frame rate of 100 Hz (2) Measurement of continuously rotating
object at a speed of 60 deg/sec