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