Analysis of system trade-offs for terahertz imaging (original) (raw)
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Optics Letters, 1995
We present what is to our knowledge the f irst imaging system based on optoelectronic terahertz time-domain spectroscopy. Terahertz time-domain waveforms are downconverted from the terahertz to the kilohertz frequency range, and the waveform for each pixel is frequency analyzed in real time with a digital signal processor to extract compositional information at that point. We demonstrate applications to package inspection and chemical content mapping in biological objects.
Advanced analysis concepts for terahertz time domain imaging
Optics Communications, 2007
Imaging based on ultrashort terahertz (THz) pulses (100-3000 lm) is investigated. The measured pulses are analyzed and the resulting amplitude and time delay information are compared. An algorithm for discrimination of multiple pulses is presented, which can distinguish several layers inside an object. A new measurement concept is presented, which accelerates the measurement of samples with small optical path differences about two orders of magnitudes. Exemplarily different applications from the field of quality management are shown.
The challenging world of Terahertz radiation and imaging
… , Proceedings of the …, 2011
THz propagation through materials may reveal unique macroscopic and physical properties of their internal structure without the damage associated with ionizing radiation. The generation, radiation, and detection of THz signals relays into an intermediate region between microwave and optical frequencies seen as a transition in device physics from classical transport to quantum transition. The physical properties and parameters of the antennas and electronic devices at these frequencies (0.1-10THz) will we compared with their microwave and optical counterparts, the important differences highlighted and its significance in terms of spectral bandwidth and signal-tonoise ratio for near and short range imaging systems reviewed. Finally, some of the recent significant developments in the field will be summarized and the potential applications and future challenges and opportunities identified.
Industrial Applications of Terahertz Imaging
Terahertz Spectroscopy and Imaging, 2012
In this chapter we provide a concise overview of potential industrial applications for terahertz imaging that have been reported over the last decade together with a discussion of the major advantages and limitations of each approach. In the second half of the chapter we discuss in more detail how terahertz imaging can be used to investigate the microstructure of pharmaceutical dosage forms. A particular focus in this context is the nondestructive measurement of the coating thickness of polymer coated tablets, both by means of high resolution off-line imaging in research and development as well as for in-line quality control during production.
18 Industrial Applications of Terahertz Imaging
2012
This chapter gives a concise overview of potential industrial applications for terahertz imaging that have been reported over the last decade with a discussion of the major advantages and limitations of each approach. In the second half of the chapter we discuss in more detail how terahertz imaging can be used to investigate the microstructure of pharmaceutical dosage forms. A particular focus in this context is the nondestructive measurement of the coating thickness of polymer coated tablets, both by means of high resolution o↵-line imaging in research and development as well as for in-line quality control during production. Published as Chapter 18 of K.E. Peiponen, J.A. Zeitler and M. KuwataGonokami (eds.), Terahertz Spectroscopy and Imaging, Springer Series in Optical Sciences, 2013, http://dx.doi.org/10.1007/978-3-642-29564-5\_18.
Wavelet based local tomographic image using terahertz techniques
Digital Signal Processing, 2009
Terahertz computed tomography has been developed based on coherent THz detection and filtered back projection (FBP) algorithms, which allows the global imaging of the internal structure and extraction of the frequency dependent properties. It offers a promising approach for achieving non-invasive inspection of solid materials. However, with traditional CT techniques, i.e. FBP algorithms, full exposure data are needed for inverting the Radon transform to produce cross sectional images. This remains true even if the region of interest is a small subset of the entire image. For time-domain terahertz measurements, the requirement for full exposure data is impractical due to the slow measurement process. This paper explores time domain reconstruction of terahertz measurements by applying wavelet-based filtered back projection algorithms for recovery of a local area of interest from terahertz measurements within its vicinity, and thus improves the feasibility of using terahertz imaging to detect defects in solid materials and diagnose disease states for clinical practise, to name a few applications.
2007 Conference on Lasers and Electro-Optics (CLEO), 2007
The methods, instrumentation, and application of time domain terahertz imaging (a.k.a. THz or TRay Imaging) for non-destructive evaluation (NDE) and security are discussed.
Measurement of coherent terahertz radiation for time-domain spectroscopy and imaging
Radiation Physics and Chemistry, 2009
A high-power terahertz (THz) source for THz time-domain spectroscopy (THz-TDS) and THz imaging has been developed based on an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). A THz pulse was generated as coherent synchrotron radiation (CSR) from an ultra-short electron bunch and expected to have peak power of kW-order with frequency range of 0.1-2 THz. The electro-optic (EO) sampling method with a ZnTe crystal for the THz pulse measurement has been prepared for THz-TDS system. The timing measurement between the THz pulse and a probe laser was carried out. A preliminary experiment of THz transmission imaging of an integrated circuit (IC) card has been successfully demonstrated using the THz CSR pulse and a W-band rf detector. The imaging result was experimentally compared with a result of X-ray imaging. It is confirmed that its intensity and stability are enough to perform for the THz applications.
A method and system for enhancing the resolution of terahertz imaging
Measurement, 2018
In this paper, a comprehensive method and process for developing Terahertz (THz) images with enhanced resolution is introduced. This method is implemented as a system comprised of various resolution and quality enhancement techniques. In this system, filters in time and frequency domains are used to filter out the noise, low-frequency spectrum, and diffraction distortions. Point Spread Function (PSF) is modeled and the quality of the output image is enhanced further through deconvolution. This process can be fully implemented on THz Time-Domain Spectroscopy (TDS) systems, and partially on continuous-wave THz imaging systems. By taking advantage of the proposed process, researchers and industrial sectors can achieve a substantial enhancement on the quality and resolution of their THz images.
Time-Frequency Analysis in Terahertz-Pulsed Imaging
Advances in Pattern Recognition
Recent advances in laser and electro-optical technologies have made the previously under-utilized terahertz frequency band of the electromagnetic spectrum accessible for practical imaging. Applications are emerging, notably in the biomedical domain. In this chapter the technique of terahertz pulsed imaging is introduced in some detail. The need for special computer vision methods, which arises from the use of pulses of radiation and the acquisition of a time series at each pixel, is described. The nature of the data is a challenge since we are interested not only in the frequency composition of the pulses, but also how these differ for different parts of the pulse. Conventional and short-time Fourier transforms and wavelets were used in preliminary experiments on the analysis of terahertz pulsed imaging data. Measurements of refractive index and absorption coefficient were compared, wavelet compression assessed and image classification by multidimensional clustering techniques demonstrated. It is shown that the timefrequency methods perform as well as conventional analysis for determining material properties. Wavelet compression gave results that were robust through compressions that used only 20% of the wavelet coefficients. It is concluded that the time-frequency methods hold great promise for optimizing the extraction of the spectroscopic information contained in each terahertz pulse, for the analysis of more complex signals comprising multiple pulses or from recently introduced acquisition techniques.