Terahertz for subsurface imaging and metrology applications

In the area of metrology and non-destructive testing, Terahertz wavelengths have been widely researched and used. However, the lack of 2D detectors working at room temperature and high power sources prevent the widespread application of Terahertz in industry. In that context, research on the development of new Terahertz equipment is moving at a fast pace. Within the scope of this thesis, applications of newly developed Terahertz technologies were explored using the scanning of single point detectors with the objective to establish the feasibility for their full-field applications in readiness for future 2D detectors. For the first time, a frequency tuneable, all-optical Terahertz source was implemented in multi-wavelength interferometry to overcome one wavelength ambiguity in precise thickness/distance measurements with sub-millimetre resolution. Phase-shifting digital holography is another interferometry technique which allows us to reconstruct not only the amplitude of one object, but also the phase and the depth of it, using existing mathematical algorithms. Digital holography was performed successfully at Terahertz wavelengths using a multiplier/mixer Terahertz source coupled with a single point pyroelectric detector for the applications of non-destructive testing and depth measurements. The novelty is that the phase-stepping technique for digital holography was implemented in THz frequencies for the first time to remove unwanted terms in the reconstructed image in order to improve image quality compare to conventional holography. In the current experiments, recording time for one set of phase-shifting holograms (4 holograms for 4 phase-steps algorithm) was 6 hours. When the technology is ready for 2D detectors, recording time of holograms could be reduced considerably, and the technique will play an important role in full-field applications in industry metrology and/or non-destructive testing and evaluation.EPSR

Versatile multimodality imaging system based on detectorless and scanless optical feedback interferometry—a retrospective overview for a prospective vision

In this retrospective compendium, we attempt to draw a “fil rouge” along fifteen years of our research in the field of optical feedback interferometry aimed at guiding the readers to the verge of new developments in the field. The general reader will be moved at appreciating the versatility and the still largely uncovered potential of the optical feedback interferometry, for both sensing and imaging applications. By discovering the broad range of available wavelengths (0.4–120 μm), the different types of suitable semiconductor lasers (Fabry–Perot, distributed feedback, vertical-cavity, quantum-cascade), and a number of unconventional tenders in multi-axis displacement, ablation front progression, self-referenced measurements, multispectral, structured light feedback imaging and compressive sensing, the specialist also could find inspirational suggestions to expand his field of research

Scan-Less, Kilo-Pixel, Line-Field Confocal Phase Imaging with Spectrally Encoded Dual-Comb Microscopy

Confocal laser microscopy (CLM) is a powerful tool in life science research and industrial inspection, and its image acquisition rate is boosted by scan-less imaging techniques. However, the optical-intensity-based image contrast in CLM makes it difficult to visualize transparent non-fluorescent objects or reflective objects with nanometer unevenness. In this paper, we introduce an optical frequency comb (OFC) to scan-less CLM to give the optical-phase-based image contrast. One-dimensional (1D) image pixels of a sample are separately encoded onto OFC modes via 1D spectral encoding by using OFC as an optical carrier of amplitude and phase with a vast number of discrete frequency channels. Then, line-field confocal information of amplitude and phase are decoded from a mode-resolved OFC amplitude and phase spectra obtained by dual-comb spectroscopy. The proposed confocal phase imaging will further expand the application fields of CLM

Scan-Less, Kilo-Pixel, Line-Field Confocal Phase Imaging with Spectrally Encoded Dual-Comb Microscopy

Confocal laser microscopy (CLM) is a powerful tool in life science research and industrial inspection, and its image acquisition rate is boosted by scan-less imaging techniques. However, the optical-intensity-based image contrast in CLM makes it difficult to visualize transparent non-fluorescent objects or reflective objects with nanometer unevenness. In this paper, we introduce an optical frequency comb (OFC) to scan-less CLM to give the optical-phase-based image contrast. One-dimensional (1D) image pixels of a sample are separately encoded onto OFC modes via 1D spectral encoding by using OFC as an optical carrier of amplitude and phase with a vast number of discrete frequency channels. Then, line-field confocal information of amplitude and phase are decoded from a mode-resolved OFC amplitude and phase spectra obtained by dual-comb spectroscopy. The proposed confocal phase imaging will further expand the application fields of CLM

Instrumentation development of innovative radio-devices to improve the coming cycles of radio astronomy observations

Radio astronomy represents one of the most useful tools for investigating celestial objects such as sychrontronic emissions from quasar , molecular clouds in the interstellar medium, and a black hole event horizon . All this is possible due to the great sensitivity that astronomical receivers can achieve, and the high angular resolution that can be reached using interferometric techniques. However, despite the great effort made, radio astronomy is not exempt of limitations that prevent it from deploying its maximum capability in terms of resolution. Atmospheric phase fluctuations, mainly induced by turbulent currents, are primarily responsible. Failure to correct these phase fluctuations will impede that the maximum potential of radio astronomy can be realized. In this thesis work, a novel solution to solve the drawbacks related to phase fluctuations in high frequency observations is presented. The ALMA telescope in Chile , has been selected as a target. The idea is to use an external optical system at room temperature, which can illuminate a low and a high frequency receiver, simultaneously. In this way, the solution for the phase fluctuation can be transferred from low to high frequency, thus, extending the maximum baseline for interferometric observations at high frequencies

Versatile Multimodality Imaging System Based on Detectorless and Scanless Optical Feedback Interferometry-A Retrospective Overview for A Prospective Vision

In this retrospective compendium, we attempt to draw a "fil rouge" along fifteen years of our research in the field of optical feedback interferometry aimed at guiding the readers to the verge of new developments in the field. The general reader will be moved at appreciating the versatility and the still largely uncovered potential of the optical feedback interferometry, for both sensing and imaging applications. By discovering the broad range of available wavelengths (0.4-120 μm), the different types of suitable semiconductor lasers (Fabry-Perot, distributed feedback, vertical-cavity, quantum-cascade), and a number of unconventional tenders in multi-axis displacement, ablation front progression, self-referenced measurements, multispectral, structured light feedback imaging and compressive sensing, the specialist also could find inspirational suggestions to expand his field of research

Application of Terahertz Pulse Time-Domain Holography for Phase Imaging

Terahertz pulse time-domain holography (THz PTDH) is the powerful technique for high-resolution amplitude and phase THz imaging that allows mapping spectroscopic information across the imaged object. In this paper, we consider most sought after applications of phase imaging provided by this technique and experimentally demonstrate the ability of the method to reconstruct smooth and stepped relief features of an object that is transparent in THz region. Unlike the amplitude distribution, which does not contain any significant information in this case, phase distribution not only reveals the object qualitatively,but also allows the reconstruction of the object thicknessespattern, even in low signal-to-noise registration conditions. Mainlimitations of the proposed method, such as transverse resolutionand low signal-to-noise environment are carefully studied and mitigated