University of Tokushima

Osaka University

Line-field terahertz computed
tomography of continuouslyrotating object
T. Yasui,1,2 Y. Ohgi,1 M. Minami,1 M. Jewariya,2M. 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	 

TST2012@Prague (2012.6.19)

University of Tokushima

Osaka University

X-ray Computed Tomography (X-ray CT)	Utility:Nondestructive inspection
Medical imaging	 

Advantage:
High penetration
Disadvantages:
Hazardous ionizing effectToo high penetration
Monochrome image→Difficult to analyze
chemical components	 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	 

Optical photograph	 

Ref) Ferguson, OL 27, 1312 (2002).	 

THz CT image	 Ref) Recur, OpEx 19, 5105 (2011).	 

University of Tokushima

Osaka University

Rapid THz color scanner equipped withreal-time line scanning of THz beam	Ref) Yasui, OpEx 16, 1208 (2008); Schirmer, Biomed. OpEx 1, 354 (2010) .	 

time-to-space conversion
in EO srystal	 Ref) Shan, OL 25, 426 (2000)	 

Line imaging of THz beamline-focused on sample	 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-timeline projection of THz beam
• Apply it for continuously rotating sample

Experimental setup

University of Tokushima

Osaka UniversityRef) Jewariya, JOSA B 26, A101 (2009)	 

LN	 

Frame rate
= 100 Hz	 2D-STTHz image	 (60 deg/sec)	 

Data acquisition condition	 
Record 600 projections line data
during 6 sec while rotating thesample continuously
by 360 degree	 THz temporalline projection	 
FBP: filtered back-projection	 University of Tokushima

TemporalWaveform

Time characteristics
Electric field [a.u.]
34000-9000 00

Temporalwaveform

Horizontal coordinate [pixel]
100200

Osaka University

0.38ps

200

10

100

0001020
Time [ps]30

Temporal line projection data(without sample)

Vertical coordinate [pixel]

Position [mm]20

Frame rate (Hz)	 
1000

100

DR

10

Cherencov radiation
in LN crystal	 

945	 
100fps	 Opt. rectificationin ZnTe crystal	 

1	 University of TokushimaOsaka University

Spectral characteristics
Line projection dataof spectral amplitude

Comparison ofamplitude spectrum

Spectral bandwidth = 3THz, Spectral resolution = 27GHz

University of Tokushima

Osaka University

Result (1): Four metallic bars (φ=2 mm)
Signal	 Sample
Strong	 Weak	 
photograph	 
Sinogram	 (a)Ep-p	 (b)20 mm	 

THzfocalline	 

Reconstructedcross-section	 

2	  mm(d)(d)(c)

Spectral
Amp. at
0.6 THz	 

Continuousrotating(360degree@6sec)	 

2	  mm360 degree	 University of Tokushima

Osaka University

Result (2): Teflon cylinder (φ=10 mm)
drilled with off-axis cylindrical hole (φ=2 mm)
SampleSignal	 Strong	 Weak	 

n=1.45, α=2cm-1	 

Sinogram	 hole	 Ep-p	 Continuous
rotating(360degree@6sec)	 

Reconstructedcross-section	 University of Tokushima

Osaka University

Result (3): Powder sample (30% lactose and70% PE) filled in off-axis hole of foam cylinder
Foam
Sample(n=1.15,α=0.1cm-1)	 

Weak	 

Powdersample	 Signal	 Strong	 Sinogram	 Reconstructedcross-section	 
4	  mmAbsorption spectrumof lactose powder(a)(b)

Spect. amp. at 0.53 THz	 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