Common path continuous terahertz reflection and attenuated total reflection imaging

Abstract

Terahertz imaging technology is one of the candidate technologies for medical imaging. In particular, continuous terahertz reflection and attenuated total reflection imaging are expected to achieve rapid intraoperative imaging, which is hot research topic at present. In order to realize the rapid multi-dimensional and high-quality terahertz imaging detection of sample, it is necessary to study the common optical path continuous terahertz reflection/attenuated total reflection dual-mode imaging system based on point scanning. By using the Fresnel formula and the penetration depth formula of evanescent wave, the influence of imaging angle on the reflected signal and the penetration depth of attenuated total reflection are studied theoretically in this paper. The imaging angle of terahertz wave suitable for both reflection and attenuation total reflection imaging is obtained. Based on this, an isoscele total reflection prism with a base angle of 49° is designed. The dual-mode imaging of common optical path continuous terahertz reflection and attenuated total reflection is realized by quickly switching between reflection window and total reflection prism. The reflection and attenuation total reflection imaging modes have imaging resolutions of 400 μm and 500 μm, respectively. Continuous terahertz reflection and attenuated total reflection imaging are experimentally studied by using distilled water and pork as samples. The results show that the relative reflectance of the sample obtained in the attenuated total reflection imaging mode fluctuates within a range of 1%, and the image contrast is 9 times that of the reflection imaging mode. Moreover, attenuated total reflection imaging can effectively identify the sample with the length less than 1 mm. Thus, compared with reflection imaging, continuous terahertz attenuated total reflection imaging has the advantages of high image resolution, high image contrast and highr signal stability, and can accurately obtain the reflectivity of sample. The terahertz attenuated total reflection imaging technology is more helpful in achieving high sensitivity imaging of samples. By combining reflection and attenuated total reflection imaging modes, the advantages of different imaging modes can be compensated for and the performance of the imaging system can be further improved. This common path continuous terahertz reflection and attenuated total reflection dual mode imaging system is expected to achieve a high sensitivity detection of sample.

Terahertz technology in intraoperative neurodiagnostics: A review

“…2(b)), while in refs. 88,89 , the ATR configuration was implemented for high-sensitive THz measurements of tissues (Fig. 2(c)).…”

“…First, in ref. 89 , temperature-dependent transmission-mode TPS and 2.52 THz CW ATR imaging were used to study orthotopic glioma model from mice ex vivo. In Fig.…”

“…Furthermore, some optimal temperatures of a tissue specimen ex vivo can be selected to improve a contrast between healthy and pathological brain tissues in the THz range (similar effect was observed earlier for the TPS and TPI measurements of 35 , Optical Society of America; (j-o) ref. 89 , under the Optica Open Access Publishing Agreement. J o u r n a l P r e -p r o o f mucosa cancer 26 ).…”

“…In (k-o), the blue boarder marks the boundary between background and a sample; while in (k), boxes 1 and 2 point areas of healthy and tumorous tissues.Figure reproduced with permission from: (a-i) ref 35 ,. Optical Society of America; (j-o) ref 89 ,. under the Op-…”

Recent Advances in THz Detection of Water

“…Optical parameters, such as the absorption coefficient [ 31 ], dielectric constant, refractive index [ 32 ], and transmittance of the sample, can be obtained from the frequency domain information using specific optical formulas [ 33 ]. According to the data processing model of Fresnel’s formula [ 34 ], the sample refractive index n(ω) and the absorption coefficient α(ω) can be calculated by the following equations: where ω is the frequency; c is the speed of light in a vacuum; d is the thickness of the sample; A(ω) denotes the amplitude ratio; and (ω) stands for the phase difference between the sample signal and the reference signal, respectively.…”