University of Tokushima

3430-IT-5

THz Color Scanner forMoving Object	
Takeshi Yasui
Univ. Tokushima, Japan	 
IQEC/CLEO Pacific Rim 2011@Sydney (2011.8.30)

University of Tokushima

Outline	 (1) Introduction(2) Experimental setup and basicperformance(3) Increase of dynamic range forfurther speeding-up of moving object(4) Application(5) Summary

University of Tokushima(1) Introduction	 University of Tokushima

Color scanner	
Spectral imaging apparatus
using visible light	 
Visible-light color scanners canprobe only in the vicinity of theobject surface.	

Utility:scanning of documents andphotographs	 Color scanner to visualizeinternal structure of opaqueobject can be achieved if highly
penetrative EM wave is used?

University of Tokushima

X-ray scanner (Radiography, CT)	Advantage:
High penetration

Utility:Nondestructive inspection
Medical imaging	 

Disadvantages:
Hazardous ionizing effectToo high penetration
Monochrome image→Difficult to analyze
chemical components	 University of Tokushima

THz color (spectroscopic) imaging
Nondestructive testing possible to analyze chemical components
Moderate penetration, insensitivity to optical scattering,
low photon energy, and spectral fingerprint
Illegal drug

ExplosiveCancer

MDMALong measurement time !
LactoseAspirin

SucroseMethamphetamine
Kawase, OpEx, 11, pp. 2549, 2003.

RDXShen, APL, 86, 24116,2005.

T. Loffler, OpEx, 9, pp. 616, 2001.

University of Tokushima

Conventional THz-TDS imaging system(Point-to-point measurement)
ML Ti:S laser

2D THz-TDS image

Probe pulse
BS

Mechanical scanning stages
・time delay

TimedelayPumppulse

・sample position

THz pulseLong acquisition timeTHz
detector

THzemitter・A few minutes@temporal waveform
・Several hours @2D imageSamplescanning

Limited to stationary objects

University of Tokushima(2) Experimental setup
and basic performance	 Ref) T. Yasui, K. Sawanaka, A. Ihara, E. Abraham, M. Hashimoto,and T. Araki, "Real-time terahertz color scanner for moving
objects," Opt. Express, Vol. 16(2), pp. 1208-1221 (2008).	 

University of Tokushima

Color (spectroscopic)
line imaging in real time(color CCD line-sensor)

Key technique!	 

Space (line sensor)

Principle of visible-light color scanner	

Space	 Two-dimensional(2D-ST)
Color line image	  color	 Scanning line-sensor spatio-temporalsample	 THz acrossimaging
based on combination of line
focusing of THz beam and time-to-spaceconversion in EO crystalRef)
Yasuda,Opt. Comm. 267, 128-136 (2006).
2D color
image	Space	 Experimental setup

University of Tokushimaθ	ref) Miyamaru, JJAP 43 (2004).

Dynamic subtraction(232*232pixel@500fps)
Line-focusingof THz beam

EO time-to-spaceconversionref) Shan, OL 25 (2000)

THzlineΔτ =Sample

Δh • tanθcUniversity of Tokushima

TemporalWaveform

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

Temporalwaveform

Horizontal coordinate [pixel]
1002000.38ps

101000001020Time [ps]30

2D-ST THz image (without sample)(measurement time = 100 ms)

DR
Dynamic range	 

200

Vertical coordinate [pixel]

Position [mm]20400@
100ms
130@
SNR10ms

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Spectral characteristics
2020

100

Position (mm)

300

0-150

10-300000

12Frequency (THz)

3

Phase (rad)Amplitude
image

Amplitude (a.u.)

Position (mm)

600

Phase
image
01

2

Frequency (THz)3Spectral bandwidth = 3THz, Spectral resolution = 29GHz

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Imaging performance
Consecutive spectral images oftest chart (line space = 0.5 mm)

Spatial resolution(NA=0.22)870µm@
430µm@
0.5THz1THz

420µm@
1.5THzSpatial resolution of THz color scanner depends on THz frequency

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4-segment metal hole array (4seg-MHA)
Metal hole array（MHA）	 Bandpass filter in THz region
Metal plate with periodic array of many holes
Passband is designed by size and interval of hole25.4 mm

0.2THzsegment

0.4THzsegment

0.2 THz
0.8 THz

1.6 THz
0.4 THz

0. 8THzsegment

1. 6THzsegment

University of Tokushima

THz spectral
imaging ofmoving 4segMHA
Samplemoving1mm/sec
0.2THz0.8THz1.6THz0.4THzTHz line
image area
20 mm×20 mm

Monochromatic THz chart

University of Tokushima

Speeding-up of moving 4seg-MHA
Sample speed = 10mm/sec (measurement time = 2sec)
Monochromatic THz chart

Consecutive THz-TDS image

University of Tokushima(3) Increase of dynamic
range for further
speeding-up of movingobject	 University of Tokushima

DR should be further increased to apply THz color
scanner for faster moving or more absorbable object!
However, our THz detection system has alreadyachieved the shot-noise limit.
Increase of THz power is a shorter way toincrease DR!
Generation of high power THz pulse using Cherenkov
radiation by tilted pulse front excitation

University of Tokushima

High power THz pulse generation
by pulse-front-tilting technique
LiNbO3 has・large nonlinear coefficient・large difference of refractive index
between optical and THz regionsref) J. Hebling, Opt. Express 10, 1161 (2002).

Effective phase matching

Modified experimental setup

University of Tokushima

800nm,	  1kHz,	  	  150fs,	  700mW	  Optical Chopper@ 500Hz	 

α=62deg	 
1.3mol%	 University of TokushimaComparison of DR between previous
and modified THz color scanners
DR of temporal waveform	 

Amplitude spectra	 

University of Tokushima

THz spectral imaging of moving 4seg-MHA
Optical rectificationin ZnTe

Sample speed=10mm/s
Image acquisition time=2sec	 

Pulse-front-tilted Cherenkov
radiation in LN

Sample speed=10mm/s
Image acquisition time=2sec	 

Sample speed=100mm/s
Image acquisition time=0.2sec	 University of Tokushima(4) Applications	 

Ref) M. Schirmer, M. Fujio, M. Minami, J. Miura, T. Araki, and T.
Yasui, "Biomedical applications of a real-time terahertz colorscanner," Biomed. Optic. Express, Vol. 1(2), pp. 354-366 (2010) .	 

Pharmaceutical tablet (1)University of Tokushima

Sugar tablets(φ10mm@1mm-thick)THz absorption spectra	 

Otsuka Electronics Co., Ltd., TR-1000 	 

Photograph of sample and holder	 Pharmaceuticaltablet (2)University of Tokushima

spectral	 ExperimentalTHz
condition	 Sample	 fingerprint (THz)	 
Sample speed=1mm/s
D-glucose	 
1.44	 
Image area = 60mm*20mm
D-maltose	 
1.10, 1.61	 
Pixel size=600*232pixels
Acquisition time= 60sec	 
Lactose	 
0.525,1.37	 
Reference	 -	 Total inspection of pharmaceuticaltablets
inmoviemanufacturing process	 THz spectral

1sttablet

2ndtablet

3rdtablet

4thtabletUniversity of Tokushima

Sliced tooth (1)	 
Experimental condition	 Sample speed=0.1mm/s
Image area = 20mm*20mm
Pixel size=200*232pixels
Acquisition time = 200sec	 

0.5 mmthicknessUniversity of Tokushima

Sliced tooth (2)	 
0.2THz	 

0.55THz	 

Indicator for crystallinity
0.55THz	 of dental tissue	 
0.25THz	 

0.25THz	 
1mm
thicknessUniversity of Tokushima

Drying progress of wet hair bundle
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Percentage of water content
in wet hair bundles	 @0.26THz	 

100d=−ln[T(ν )]α (ν )Lsample€α(ν): absorption coefficient of water=130cm-1 @ 0.26THz
Lsample: effective thickness of hair bundles=0.2mmΤ(ν): power transmittance of hair bundles

Sensitive probe
for water content
Bundles	 ofBundles ofwet hairs

dry hairs

University of Tokushima

Summary	

(1) THz color scanner equipped with real-timeline-scanning(2) Can be used for moving object at 100mm/s(3) Applications
・Rapid inspection of pharmaceutical tablets
・Indicator for crystallinity of dental tissue
・Sensitive probe for water content
Acknowledgement
We thank Dr. M. Nagai (Kyoto Univ.) and Prof. J. Hebling (Univ. ofPécs) for useful discussion on Cherenkov radiation.