THz Fiber-Scanning Near-Field Microscopy
Date Issued
2009
Date
2009
Author(s)
Chiu, Chui-Min
Abstract
Within the last several years, terahertz (THz) science and technology has been attracting much attention for various biomedical applications, such as THz spectroscopy, sensing and imaging of biological molecules and tissues, because different bio-molecules have their distinctive absorption spectra in the THz frequency range. In addition, THz radiation is non-ionizing, and the power levels are many orders of magnitude less than the recommended safety guidelines. Therefore, compared with conventional imaging techniques such as X-ray imaging, THz imaging is believed to be a safe and non-invasive technique.To date, most of the THz imaging systems has been constructed by many metal reflectors fixed on optical tabletop, and thus THz waves could propagate between these mirrors in free space. THz imaging is performed by moving the sample in front of the focused THz beam by means of a computer-controlled two-dimensional translation stage. This imaging system (sample-scanning) may restrict the future development and the practicability into living tissue, because samples are not always movable in most biomedical imaging applications. Moving the objects, especially in the form of powder or liquid or live biological specimens, sometimes will also disturb the sample frequently. A beam scanning THz imaging system is thus extremely needed.Recently, we proposed an alternative method which was based on our demonstrated low-loss sub-wavelength polyethylene (PE) fiber to construct a fiber-scanning THz imaging system which has advantages of compact size, all room-temperature operation, high SNR, reasonable spatial resolution, and without moving the imaged objects. The demonstrated THz sub-wavelength PE fiber has advantages including: ease of fabrication, low attenuation constant (< 0.01cm-1), low bending loss, and with a high free space coupling efficiency (typically about 50%). THz waves could be long-distance guided along the sub-wavelength fiber to the sample region and THz images would be acquired by directly 2D scanning of the THz fiber output end.However, the spatial resolution of THz imaging is limited by the wavelength (0.3mm at 1THz). To improve the spatial resolution, a near-field technology is required, similar to the scanning near-field optical microscopy (SNOM). Hence, based on a fiber-scanning THz imaging system with an optimally designed plasmon-resonance bull’s-eye metallic spatial filter, which is consisted of a single sub-wavelength aperture surrounded by the concentric periodic grooves, we report the first ever demonstration of the transmission-illumination mode of an upright-type all-THz fiber-scanning near-field microscope with a compact size operating at room-temperature, which is capable to be integrated with a common optical microscope. Samples can be observed by the optical microscope immediately without moving after fiber scanning for a THz near-field image. By applying this trans-illumination imaging system to the examination of human breast sections, our preliminary results show that this near-field imaging system could clearly and accurately distinguish between breast cancerous tissues from normal tissues in the same section without any pathologic staining. The distribution regions of breast cancer are also in excellent agreement with pathologic diagnosis by using H&E staining.In the clinical applications, the demonstrated THz near-field imaging system could help to more accurately define the margins of cancer, minimize the size of normal tissues excised in the breast-conserving surgery (BCS), and reduce the need for any additional surgery procedures.
Subjects
Single-Mode Fiber
THz Imaging
Surface Plasmon Polaritons
Near-Field Microscopy
Breast Cancer
SDGs
Type
thesis
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