D. Damyanov, B. Friederich, K. Kolpatzeck, Xuan Liu, A. Czylwik, T. Schultze, I. Willms, J. Balzer
Terahertz time-domain systems are known as a precise imaging tool. These systems make use of parabolic mirrors or lenses to illuminate a small spot of a sample under test. By moving the sample or the sensor head, an image can be recorded. This imaging technique guarantees a high signal-to-noise ratio and large bandwidth. However, using this method a priori knowledge of the sample shape is needed for the correct focusing of the system. This limits the performance and robustness of the imaging system as only specular reflections are considered for the image. Here, we propose a fast reflection-based broadband terahertz time-domain imaging method that overcomes these hurdles by making use of both the specular and diffuse reflections of a divergent terahertz beam. The proposed method employs no optical lenses or mirrors but uses signal processing and classical radar migration techniques. High-resolution imaging is achieved by focusing the divergent terahertz beam via post-processing. To compensate the inherent poor signal-to-noise ratio of the unfocused terahertz beam, calibration and post-processing methods are used. For the evaluation of the imaging method, geometrically complex samples are scanned by a fast terahertz time-domain spectroscopy system based on electronically controlled optical sampling. The bandwidth achieved with the divergent beam is 2.5 THz with a signal-to-noise ratio of around 30 dB. We demonstrate that this method is capable to generate high-resolution 2D terahertz images of objects with arbitrary size, shape, orientation and relative position to the emitter and detector antennas. Objects with sub-mm dimension can be clearly reconstructed for arbitrary positions and orientation achieving resolution in the µm region. Furthermore, the presented method can be applied for any reflection-based scenarios and antenna configuration.
{"title":"A novel approach for lensless high-resolution terahertz imaging (Conference Presentation)","authors":"D. Damyanov, B. Friederich, K. Kolpatzeck, Xuan Liu, A. Czylwik, T. Schultze, I. Willms, J. Balzer","doi":"10.1117/12.2554007","DOIUrl":"https://doi.org/10.1117/12.2554007","url":null,"abstract":"Terahertz time-domain systems are known as a precise imaging tool. These systems make use of parabolic mirrors or lenses to illuminate a small spot of a sample under test. By moving the sample or the sensor head, an image can be recorded. This imaging technique guarantees a high signal-to-noise ratio and large bandwidth. However, using this method a priori knowledge of the sample shape is needed for the correct focusing of the system. This limits the performance and robustness of the imaging system as only specular reflections are considered for the image. Here, we propose a fast reflection-based broadband terahertz time-domain imaging method that overcomes these hurdles by making use of both the specular and diffuse reflections of a divergent terahertz beam. The proposed method employs no optical lenses or mirrors but uses signal processing and classical radar migration techniques. High-resolution imaging is achieved by focusing the divergent terahertz beam via post-processing. To compensate the inherent poor signal-to-noise ratio of the unfocused terahertz beam, calibration and post-processing methods are used. For the evaluation of the imaging method, geometrically complex samples are scanned by a fast terahertz time-domain spectroscopy system based on electronically controlled optical sampling. The bandwidth achieved with the divergent beam is 2.5 THz with a signal-to-noise ratio of around 30 dB. We demonstrate that this method is capable to generate high-resolution 2D terahertz images of objects with arbitrary size, shape, orientation and relative position to the emitter and detector antennas. Objects with sub-mm dimension can be clearly reconstructed for arbitrary positions and orientation achieving resolution in the µm region. Furthermore, the presented method can be applied for any reflection-based scenarios and antenna configuration.","PeriodicalId":113454,"journal":{"name":"Terahertz Photonics","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124673974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sarah Houver, Lucas Huber, Matteo Savoini, Elsa Abreu, Steven L. Johnson
In semiconductors and semimetals, strong THz electric fields can induce a controlled coherent motion of the electrons in the conduction band, via ballistic excitation. In the first picoseconds after THz excitation, the nonlinearities induced by this coherent excitation prevail before more incoherent high field effects start dominating the nonlinear response. Disentangling these different nonlinear contributions with 2D THz spectroscopy, we follow the trajectory of the out-of-equilibrium electron population in low-bandgap semiconductor InSb and. We then extract information on the conduction band curvature and evaluate its anharmonicity and its anisotropy, close to the Gamma-point.
{"title":"2D THz spectroscopic investigation of ballistic conduction-band electron dynamics in InSb (Conference Presentation)","authors":"Sarah Houver, Lucas Huber, Matteo Savoini, Elsa Abreu, Steven L. Johnson","doi":"10.1117/12.2543969","DOIUrl":"https://doi.org/10.1117/12.2543969","url":null,"abstract":"In semiconductors and semimetals, strong THz electric fields can induce a controlled coherent motion of the electrons in the conduction band, via ballistic excitation. In the first picoseconds after THz excitation, the nonlinearities induced by this coherent excitation prevail before more incoherent high field effects start dominating the nonlinear response. Disentangling these different nonlinear contributions with 2D THz spectroscopy, we follow the trajectory of the out-of-equilibrium electron population in low-bandgap semiconductor InSb and. We then extract information on the conduction band curvature and evaluate its anharmonicity and its anisotropy, close to the Gamma-point.","PeriodicalId":113454,"journal":{"name":"Terahertz Photonics","volume":" 32","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141223790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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