1
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Qi X, Bertling K, Torniainen J, Kong F, Gillespie T, Primiero C, Stark MS, Dean P, Indjin D, Li LH, Linfield EH, Davies AG, Brünig M, Mills T, Rosendahl C, Soyer HP, Rakić AD. Terahertz in vivo imaging of human skin: Toward detection of abnormal skin pathologies. APL Bioeng 2024; 8:016117. [PMID: 38476403 PMCID: PMC10932572 DOI: 10.1063/5.0190573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Accepted: 02/19/2024] [Indexed: 03/14/2024] Open
Abstract
Terahertz (THz) imaging has long held promise for skin cancer detection but has been hampered by the lack of practical technological implementation. In this article, we introduce a technique for discriminating several skin pathologies using a coherent THz confocal system based on a THz quantum cascade laser. High resolution in vivo THz images (with diffraction limited to the order of 100 μm) of several different lesion types were acquired and compared against one another using the amplitude and phase values. Our system successfully separated pathologies using a combination of phase and amplitude information and their respective surface textures. The large scan field (50 × 40 mm) of the system allows macroscopic visualization of several skin lesions in a single frame. Utilizing THz imaging for dermatological assessment of skin lesions offers substantial additional diagnostic value for clinicians. THz images contain information complementary to the information contained in the conventional digital images.
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Affiliation(s)
- X. Qi
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - K. Bertling
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - J. Torniainen
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - F. Kong
- Dermatology Research Centre, Frazer Institute, The University of Queensland, Woolloongabba QLD 4102, Australia
| | - T. Gillespie
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - C. Primiero
- Dermatology Research Centre, Frazer Institute, The University of Queensland, Woolloongabba QLD 4102, Australia
| | - M. S. Stark
- Dermatology Research Centre, Frazer Institute, The University of Queensland, Woolloongabba QLD 4102, Australia
| | - P. Dean
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - D. Indjin
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - L. H. Li
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - E. H. Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - A. G. Davies
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - M. Brünig
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - T. Mills
- OscillaDx Pty Ltd, Brisbane, Queensland, Australia
| | - C. Rosendahl
- General Practice Clinical Unit, Faculty of Medicinee, The University of Queensland, Herston QLD 4029, Australia
| | - H. P. Soyer
- Dermatology Research Centre, Frazer Institute, The University of Queensland, Woolloongabba QLD 4102, Australia
| | - A. D. Rakić
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
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2
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Mohun D, Sulollari N, Salih M, Li LH, Cunningham JE, Linfield EH, Davies AG, Dean P. Terahertz microscopy using laser feedback interferometry based on a generalised phase-stepping algorithm. Sci Rep 2024; 14:3274. [PMID: 38332232 PMCID: PMC10853214 DOI: 10.1038/s41598-024-53448-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Accepted: 01/31/2024] [Indexed: 02/10/2024] Open
Abstract
In this paper we report an improved method of coherent sensing through the use of a generalized phase-stepping algorithm to extract magnitude and phase information from interferometric fringes acquired by laser feedback interferometry (LFI). Our approach allows for significantly reduced optical sampling and acquisition times whilst also avoiding the need for fitting to complex models of lasers under optical feedback in post-processing. We investigate theoretically the applicability of this method under different levels of optical feedback, different laser parameters, and for different sampling conditions. We furthermore validate its use experimentally for LFI-based sensing using a terahertz (THz)-frequency laser in both far-field and near-field sensing configurations. Finally we demonstrate our approach for two-dimensional nanoscale imaging of the out-of-plane field supported by individual micro-resonators at THz frequencies. Our results show that fully coherent sensing can be achieved reliably with as little as 4 sampling points per imaging pixel, opening up opportunities for fast coherent sensing not only at THz frequencies but across the visible and infra-red spectrum.
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Affiliation(s)
- Daniel Mohun
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Nikollao Sulollari
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Mohammed Salih
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Lianhe H Li
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - John E Cunningham
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Edmund H Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - A Giles Davies
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Paul Dean
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK.
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3
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Bertling K, Veidt M, Perchoux J, Rakić AD. Imaging elastic waves in solids: how to use laser feedback interferometry to visualize them. OPTICS EXPRESS 2023; 31:32761-32771. [PMID: 37859071 DOI: 10.1364/oe.497676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 09/07/2023] [Indexed: 10/21/2023]
Abstract
The use of ultrasonic elastic waves is a well established technique for non-destructive testing of materials and structures, in particular to exploit the interaction of waves with structural features to detect and characterize defects. Optical methods offer the advantage of visualising the distribution of elastic waves in a non-contact manner without disturbing the elastic wave. In this work we propose a laser feedback interferometry (LFI) based system as a cost effective, non-contact, alternative to a well established laser Doppler vibrometer technique. We demonstrate the visualization of the elastic waves, using an example of an elastic wave propagating through a prismatic acrylic rod. We show that the ultra-compact and simple implementation of LFI enables accurate visualization of the elastic waves in solids, and opens the pathway to a range of new opportunities in ultrasonic non-destructive testing and evaluation.
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4
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Kashyap M, Torniainen J, Bertling K, Kundu U, Singh K, Donose BC, Gillespie T, Lim YL, Indjin D, Li L, Linfield EH, Davies AG, Dean P, Smith M, Chapman S, Bandyopadhyay A, Sengupta A, Rakić AD. Coherent terahertz laser feedback interferometry for hydration sensing in leaves. OPTICS EXPRESS 2023; 31:23877-23888. [PMID: 37475228 DOI: 10.1364/oe.490217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Accepted: 06/08/2023] [Indexed: 07/22/2023]
Abstract
The response of terahertz to the presence of water content makes it an ideal analytical tool for hydration monitoring in agricultural applications. This study reports on the feasibility of terahertz sensing for monitoring the hydration level of freshly harvested leaves of Celtis sinensis by employing a imaging platform based on quantum cascade lasers and laser feedback interferometry. The imaging platform produces wide angle high resolution terahertz amplitude and phase images of the leaves at high frame rates allowing monitoring of dynamic water transport and other changes across the whole leaf. The complementary information in the resulting images was fed to a machine learning model aiming to predict relative water content from a single frame. The model was used to predict the change in hydration level over time. Results of the study suggest that the technique could have substantial potential in agricultural applications.
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5
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Qi X, Bertling K, Stark MS, Taimre T, Kao YC, Lim YL, Han S, O’Brien B, Collins A, Walsh M, Torniainen J, Gillespie T, Donose BC, Dean P, Li LH, Linfield EH, Davies AG, Indjin D, Soyer HP, Rakić AD. Terahertz imaging of human skin pathologies using laser feedback interferometry with quantum cascade lasers. BIOMEDICAL OPTICS EXPRESS 2023; 14:1393-1410. [PMID: 37078035 PMCID: PMC10110320 DOI: 10.1364/boe.480615] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 01/31/2023] [Accepted: 02/03/2023] [Indexed: 05/03/2023]
Abstract
Early detection of skin pathologies with current clinical diagnostic tools is challenging, particularly when there are no visible colour changes or morphological cues present on the skin. In this study, we present a terahertz (THz) imaging technology based on a narrow band quantum cascade laser (QCL) at 2.8 THz for human skin pathology detection with diffraction limited spatial resolution. THz imaging was conducted for three different groups of unstained human skin samples (benign naevus, dysplastic naevus, and melanoma) and compared to the corresponding traditional histopathologic stained images. The minimum thickness of dehydrated human skin that can provide THz contrast was determined to be 50 µm, which is approximately one half-wavelength of the THz wave used. The THz images from different types of 50 µm-thick skin samples were well correlated with the histological findings. The per-sample locations of pathology vs healthy skin can be separated from the density distribution of the corresponding pixels in the THz amplitude-phase map. The possible THz contrast mechanisms relating to the origin of image contrast in addition to water content were analyzed from these dehydrated samples. Our findings suggest that THz imaging could provide a feasible imaging modality for skin cancer detection that is beyond the visible.
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Affiliation(s)
- Xiaoqiong Qi
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Karl Bertling
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Mitchell S. Stark
- The University of Queensland Diamantina Institute, The University of Queensland, Dermatology Research Centre, Brisbane, QLD 4102, Australia
| | - Thomas Taimre
- School of Mathematics and Physics, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Yung-Ching Kao
- The University of Queensland Diamantina Institute, The University of Queensland, Dermatology Research Centre, Brisbane, QLD 4102, Australia
| | - Yah Leng Lim
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - She Han
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Blake O’Brien
- Sullivan Nicolaides Pathology, Brisbane, QLD, Australia
| | - Angus Collins
- Sullivan Nicolaides Pathology, Brisbane, QLD, Australia
| | - Michael Walsh
- Sullivan Nicolaides Pathology, Brisbane, QLD, Australia
| | - Jari Torniainen
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Timothy Gillespie
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Bogdan C. Donose
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Paul Dean
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - Lian He Li
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - Edmund H. Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - A. Giles Davies
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - Dragan Indjin
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - H. Peter Soyer
- The University of Queensland Diamantina Institute, The University of Queensland, Dermatology Research Centre, Brisbane, QLD 4102, Australia
- Department of Dermatology, Princess Alexandra Hospital, Brisbane, Queensland, Australia
| | - Aleksandar D. Rakić
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
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6
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Singh K, Bandyopadhyay A, Bertling K, Lim YL, Gillespie T, Indjin D, Li L, Linfield EH, Davies AG, Dean P, Rakić AD, Sengupta A. Comparison of Physical and System Factors Impacting Hydration Sensing in Leaves Using Terahertz Time-Domain and Quantum Cascade Laser Feedback Interferometry Imaging. SENSORS (BASEL, SWITZERLAND) 2023; 23:2721. [PMID: 36904925 PMCID: PMC10007308 DOI: 10.3390/s23052721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 02/24/2023] [Accepted: 02/28/2023] [Indexed: 06/18/2023]
Abstract
To reduce the water footprint in agriculture, the recent push toward precision irrigation management has initiated a sharp rise in photonics-based hydration sensing in plants in a non-contact, non-invasive manner. Here, this aspect of sensing was employed in the terahertz (THz) range for mapping liquid water in the plucked leaves of Bambusa vulgaris and Celtis sinensis. Two complementary techniques, broadband THz time-domain spectroscopic imaging and THz quantum cascade laser-based imaging, were utilized. The resulting hydration maps capture the spatial variations within the leaves as well as the hydration dynamics in various time scales. Although both techniques employed raster scanning to acquire the THz image, the results provide very distinct and different information. Terahertz time-domain spectroscopy provides rich spectral and phase information detailing the dehydration effects on the leaf structure, while THz quantum cascade laser-based laser feedback interferometry gives insight into the fast dynamic variation in dehydration patterns.
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Affiliation(s)
- Khushboo Singh
- Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
| | - Aparajita Bandyopadhyay
- DRDO-Industry-Academia Center of Excellence, Indian Institute of Technology Delhi, New Delhi 110016, India
| | - Karl Bertling
- School of Information Technology & Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Yah Leng Lim
- School of Information Technology & Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Tim Gillespie
- School of Information Technology & Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Dragan Indjin
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - Lianhe Li
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - Edmund H. Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - A. Giles Davies
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - Paul Dean
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - Aleksandar D. Rakić
- School of Information Technology & Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Amartya Sengupta
- Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
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7
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Bertling K, Qi X, Taimre T, Lim YL, Rakić AD. Feedback Regimes of LFI Sensors: Experimental Investigations. SENSORS (BASEL, SWITZERLAND) 2022; 22:9001. [PMID: 36433597 PMCID: PMC9696093 DOI: 10.3390/s22229001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 11/11/2022] [Accepted: 11/18/2022] [Indexed: 06/16/2023]
Abstract
In this article, we revisit the concept of optical feedback regimes in diode lasers and explore each regime experimentally from a somewhat unconventional point of view by relating the feedback regimes to the laser bias current and its optical feedback level. The results enable setting the operating conditions of the diode laser in different applications requiring operation in different feedback regimes. We experimentally explored and theoretically supported this relationship from the standard Lang and Kobayashi rate equation model for a laser diode under optical feedback. All five regimes were explored for two major types of laser diodes: inplane lasers and vertical-cavity surface emitting lasers. For both lasers, we mapped the self-mixing strength vs. drive current and feedback level, observed the differences in the shape of the self-mixing fringes between the two laser architectures and a general simulation, and monitored other parameters of the lasers with changing optical feedback.
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Affiliation(s)
- Karl Bertling
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Xiaoqiong Qi
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Thomas Taimre
- School of Mathematics and Physics, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Yah Leng Lim
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Aleksandar D. Rakić
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
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8
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Qi X, Loh HY, Taimre T, Bertling K, Indjin D, Rakić AD. Self-Pulsations in Terahertz Quantum Cascade Lasers under Strong Optical Feedback: The Effect of Multiple Reflections in the External Cavity. SENSORS (BASEL, SWITZERLAND) 2022; 22:8501. [PMID: 36366193 PMCID: PMC9658095 DOI: 10.3390/s22218501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 10/29/2022] [Accepted: 11/03/2022] [Indexed: 06/16/2023]
Abstract
We have recently reported the self-pulsation phenomenon under strong optical feedback in terahertz (THz) quantum cascade lasers (QCLs). One important issue, however, we left open: the effect of multiple round trips in the external cavity on the laser response to feedback. Our current analysis also casts additional light on the phenomenon of self-pulsations. Using only one external cavity round trip (ECRT) in the model has been the common approach following the seminal paper by Lang-Kobayashi in 1980. However, the conditions under which the Lang-Kobayashi model, in its original single-ECRT formulation, is applicable has been rarely explored. In this work, we investigate the self-pulsation phenomenon under multiple ECRTs. We found that the self-pulsation waveform changes when considering more than one ECRT. This we attribute to the combined effect of the extended external cavity length and the frequency modulation of the pulsation frequency by the optical feedback. Our findings add to the understanding of the optical feedback dynamics under multiple ECRTs and provide a pathway for selecting the appropriate numerical model to study the optical feedback dynamics in THz QCLs and semiconductor lasers in general.
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Affiliation(s)
- Xiaoqiong Qi
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Hui Yi Loh
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Thomas Taimre
- School of Mathematics and Physics, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Karl Bertling
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Dragan Indjin
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - Aleksandar D. Rakić
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
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9
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Tollkühn M, Ritter PJ, Schilling M, Hampel B. THz microscope for three-dimensional imaging with superconducting Josephson junctions. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:043708. [PMID: 35489904 DOI: 10.1063/5.0084207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Accepted: 04/03/2022] [Indexed: 06/14/2023]
Abstract
Superconducting Josephson junctions have a wide range of applications ranging from quantum computing to voltage standards, and they may also be employed as versatile sensors for high-frequency radiation and magnetic fields. In this work, we present a unique measurement setup utilizing a single Josephson junction on a cantilever for high-resolution spatial measurements of spectroscopically resolved THz and microwave field distributions. This THz microscope can be utilized to measure power and frequency of electromagnetic radiation from ∼1 GHz to 5 THz. It may also be used to measure static magnetic fields and provide topological scans of samples. The samples can be both actively radiating or passively irradiated at either room temperature or cryogenic temperatures. We review the measurement setup of the THz microscope and describe the evaluation of its measurement data to achieve three-dimensional visualizations of the field distributions. The diverse capabilities of this unique tool are demonstrated by its different measurement modes with measurements of field distributions at 20 GHz and 1.4 THz, spectroscopically resolved THz measurements, and magnetic field measurements.
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Affiliation(s)
- M Tollkühn
- Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, 38106 Braunschweig, Germany
| | - P J Ritter
- Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, 38106 Braunschweig, Germany
| | - M Schilling
- Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, 38106 Braunschweig, Germany
| | - B Hampel
- Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, 38106 Braunschweig, Germany
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10
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Wang D, Ning R, Li G, Zhao J, Wang Y, Rong L. 3D image reconstruction of terahertz computed tomography at sparse angles by total variation minimization. APPLIED OPTICS 2022; 61:B1-B7. [PMID: 35201119 DOI: 10.1364/ao.440847] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Accepted: 10/09/2021] [Indexed: 06/14/2023]
Abstract
Continuous-wave terahertz computed tomography (THz-CT) is an important three-dimensional imaging method for probing the profile and inner properties of a sample's structure. We applied the total variation (TV) minimization iterative algorithm to squeeze 75% data acquisition time of THz-CT without the loss of reconstruction fidelity. The imaging system is built based on a 278.6 GHz avalanche diode source. A zero-order Bessel beam is generated by an axicon, for which the intensity profile remains essentially propagation invariant within the non-diffracting zone. The effectiveness of the proposed method is verified by using three optically opaque objects. The reconstruction results show that the TV-minimization algorithm can effectively suppress noise, artefacts, and shape distortion created in sparse angle reconstruction.
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11
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Rong L, Wang S, Wang D, Tan F, Zhang Y, Zhao J, Wang Y. Transport of intensity equation-based terahertz lensless full-field phase imaging. OPTICS LETTERS 2021; 46:5846-5849. [PMID: 34851905 DOI: 10.1364/ol.442625] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Accepted: 10/26/2021] [Indexed: 06/13/2023]
Abstract
Terahertz (THz) phase imaging is widely spreading in various scenarios, among which full-field phase distributions are commonly retrieved by digital holography or ptychography. In this Letter, the transport of the intensity equation reconstruction method is applied into the THz band. An algorithm named the lensless US-transport of intensity equation (TIE) is proposed to accommodate to an in-line configuration. The object phase is retrieved by primarily conducting iterations between the axial intensity derivative and the phase distribution at the recording plane and subsequent backward diffraction propagation. This method is applicable to both isolated and extended weakly absorbing samples with higher reconstruction quality and remarkably less time cost than holographic phase retrieval algorithms. It can also be attempted in other non-interferometric geometries or using low-cost partially coherent THz sources, which significantly broaden the application scope of THz phase imaging.
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12
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Qi X, Bertling K, Taimre T, Agnew G, Leng Lim Y, Gillespie T, Demić A, Dean P, He Li L, Linfield EH, Giles Davies A, Indjin D, Rakić AD. Terahertz quantum cascade laser under optical feedback: effects of laser self-pulsations on self-mixing signals. OPTICS EXPRESS 2021; 29:39885-39895. [PMID: 34809343 DOI: 10.1364/oe.437861] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Accepted: 09/27/2021] [Indexed: 06/13/2023]
Abstract
In this article, we explore the interplay between the self-pulsations (SPs) and self-mixing (SM) signals generated in terahertz (THz) quantum cascade lasers (QCLs) under optical feedback. We find that optical feedback dynamics in a THz QCL, namely, SPs, modulate the conventional SM interference fringes in a laser feedback interferometry system. The phenomenon of fringe loss in the SM signal - well known in interband diode lasers - was also observed along with pronounced SPs. With an increasing optical feedback strength, SM interference fringes transition from regular fringes at weak feedback (C ≤ 1) to fringes modulated by SPs under moderate feedback (1 < C ≤ 4.6), and then [under strong feedback (C > 4.6)] to a SM waveform with reduced number of fringes modulated by SP, until eventually (under even greater feedback) all the fringes are lost and only SPs are left visible. The transition route described above was identified in simulation when the SM fringes are created either by a moving target or a current modulation of the THz QCL. This SM signal transition route was successfully validated experimentally in a pulsed mode THz QCL with SM fringes created by current modulation during the pulse. The effects of SP dynamics in laser feedback interferometric system investigated in this work not only provides a further understanding of nonlinear dynamics in a THz QCL but also helps to understand the SM waveforms generated in a THz QCLs when they are used for various sensing and imaging applications.
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Abstract
Terahertz (THz) radiation is poised to have an essential role in many imaging applications, from industrial inspections to medical diagnosis. However, commercialization is prevented by impractical and expensive THz instrumentation. Single-pixel cameras have emerged as alternatives to multi-pixel cameras due to reduced costs and superior durability. Here, by optimizing the modulation geometry and post-processing algorithms, we demonstrate the acquisition of a THz-video (32 × 32 pixels at 6 frames-per-second), shown in real-time, using a single-pixel fiber-coupled photoconductive THz detector. A laser diode with a digital micromirror device shining visible light onto silicon acts as the spatial THz modulator. We mathematically account for the temporal response of the system, reduce noise with a lock-in free carrier-wave modulation and realize quick, noise-robust image undersampling. Since our modifications do not impose intricate manufacturing, require long post-processing, nor sacrifice the time-resolving capabilities of THz-spectrometers, their greatest asset, this work has the potential to serve as a foundation for all future single-pixel THz imaging systems. Terahertz imaging is promising in many applications, but still relies on complex equipment. Here, the authors develop a simplified solution that enables terahertz real-time imaging using a single-pixel detector and rapid reconstruction methods.
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14
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Valzania L, Zhao Y, Rong L, Wang D, Georges M, Hack E, Zolliker P. THz coherent lensless imaging. APPLIED OPTICS 2019; 58:G256-G275. [PMID: 31873509 DOI: 10.1364/ao.58.00g256] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 09/28/2019] [Indexed: 06/10/2023]
Abstract
Imaging with THz radiation has proved an important tool for both fundamental science and industrial use. Here we review a class of THz imaging implementations, named coherent lensless imaging, that reconstruct the coherent response of arbitrary samples with a minimized experimental setup based only on a coherent source and a camera. After discussing the appropriate sources and detectors to perform them, we detail the fundamental principles and implementations of THz digital holography and phase retrieval. These techniques owe a lot to imaging with different wavelengths, yet innovative concepts are also being developed in the THz range and are ready to be applied in other spectral ranges. This makes our review useful for both the THz and imaging communities, and we hope it will foster their interaction.
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Zhang Z, Li C, Huang Z. Quadrature demodulation based on lock-in amplifier technique for self-mixing interferometry displacement sensor. APPLIED OPTICS 2019; 58:6098-6104. [PMID: 31503931 DOI: 10.1364/ao.58.006098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 07/11/2019] [Indexed: 06/10/2023]
Abstract
A new self-mixing interferometry quadrature demodulation method based on a lock-in amplifier technique is proposed. Sinusoidal phase modulation of the beam is obtained by an electro-optic modulator (EOM) in the external cavity. Then the real phase of the external target can be calculated by lock-in amplifier analysis method. In this paper, the validity of the proposed method is confirmed by theoretical analysis and means of simulated signals, and then it is demonstrated by several experimental measurements for target harmonic and arbitrary motion. The results show that the proposed method can get a high-precision measurement, even using a diffusive target.
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Keeley J, Bertling K, Rubino PL, Lim YL, Taimre T, Qi X, Kundu I, Li LH, Indjin D, Rakić AD, Linfield EH, Davies AG, Cunningham J, Dean P. Detection sensitivity of laser feedback interferometry using a terahertz quantum cascade laser. OPTICS LETTERS 2019; 44:3314-3317. [PMID: 31259948 DOI: 10.1364/ol.44.003314] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Accepted: 05/08/2019] [Indexed: 06/09/2023]
Abstract
We report on the high detection sensitivity of a laser feedback interferometry scheme based on a terahertz frequency quantum cascade laser (QCL). We show that variations on the laser voltage induced by optical feedback to the laser can be resolved with the reinjection of powers as low as ∼-125 dB of the emitted power. Our measurements demonstrate a noise equivalent power of ∼1.4 pW/√Hz, although, after accounting for the reinjection losses, we estimate that this corresponds to only ∼1 fW/√Hz being coupled to the QCL active region.
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