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Willenberg B, Phillips CR, Pupeikis J, Camenzind SL, Liebermeister L, Kohlhass RB, Globisch B, Keller U. THz-TDS with gigahertz Yb-based dual-comb lasers: noise analysis and mitigation strategies. APPLIED OPTICS 2024; 63:4144-4156. [PMID: 38856508 DOI: 10.1364/ao.522802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Accepted: 04/26/2024] [Indexed: 06/11/2024]
Abstract
We investigate terahertz time-domain spectroscopy using a low-noise dual-frequency-comb laser based on a single spatially multiplexed laser cavity. The laser cavity includes a reflective biprism, which enables generation of a pair of modelocked output pulse trains with slightly different repetition rates and highly correlated noise characteristics. These two pulse trains are used to generate the THz waves and detect them by equivalent time sampling. The laser is based on Yb:CALGO, operates at a nominal repetition rate of 1.18 GHz, and produces 110 mW per comb with 77 fs pulses around 1057 nm. We perform THz measurements with Fe-doped photoconductive antennas, operating these devices with gigahertz 1 µm lasers for the first time, to our knowledge, and obtain THz signal currents approximately as strong as those from reference measurements at 1.55 µm and 80 MHz. We investigate the influence of the laser's timing noise properties on THz measurements, showing that the laser's timing jitter is quantitatively explained by power-dependent shifts in center wavelength. We demonstrate reduction in noise by simple stabilization of the pump power and show up to 20 dB suppression in noise by the combination of shared pumping and shared cavity architecture. The laser's ultra-low-noise properties enable averaging of the THz waveform for repetition rate differences from 1 kHz to 22 kHz, resulting in a dynamic range of 55 dB when operating at 1 kHz and averaging for 2 s. We show that the obtained dynamic range is competitive and can be well explained by accounting for the measured optical delay range, integration time, as well as the measurement bandwidth dependence of the noise from transimpedance amplification. These results will help enable a new approach to high-resolution THz-TDS enabled by low-noise gigahertz dual-comb lasers.
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Li X, Li J, Li Y, Ozcan A, Jarrahi M. High-throughput terahertz imaging: progress and challenges. LIGHT, SCIENCE & APPLICATIONS 2023; 12:233. [PMID: 37714865 PMCID: PMC10504281 DOI: 10.1038/s41377-023-01278-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2023] [Revised: 08/04/2023] [Accepted: 08/28/2023] [Indexed: 09/17/2023]
Abstract
Many exciting terahertz imaging applications, such as non-destructive evaluation, biomedical diagnosis, and security screening, have been historically limited in practical usage due to the raster-scanning requirement of imaging systems, which impose very low imaging speeds. However, recent advancements in terahertz imaging systems have greatly increased the imaging throughput and brought the promising potential of terahertz radiation from research laboratories closer to real-world applications. Here, we review the development of terahertz imaging technologies from both hardware and computational imaging perspectives. We introduce and compare different types of hardware enabling frequency-domain and time-domain imaging using various thermal, photon, and field image sensor arrays. We discuss how different imaging hardware and computational imaging algorithms provide opportunities for capturing time-of-flight, spectroscopic, phase, and intensity image data at high throughputs. Furthermore, the new prospects and challenges for the development of future high-throughput terahertz imaging systems are briefly introduced.
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Affiliation(s)
- Xurong Li
- Department of Electrical & Computer Engineering, University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
| | - Jingxi Li
- Department of Electrical & Computer Engineering, University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
- Department of Bioengineering, University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
| | - Yuhang Li
- Department of Electrical & Computer Engineering, University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
- Department of Bioengineering, University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
| | - Aydogan Ozcan
- Department of Electrical & Computer Engineering, University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
- Department of Bioengineering, University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA
| | - Mona Jarrahi
- Department of Electrical & Computer Engineering, University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA.
- California NanoSystems Institute (CNSI), University of California Los Angeles (UCLA), Los Angeles, CA, 90095, USA.
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Cherniak V, Kubiczek T, Kolpatzeck K, Balzer JC. Laser diode based THz-TDS system with 133 dB peak signal-to-noise ratio at 100 GHz. Sci Rep 2023; 13:13476. [PMID: 37596348 PMCID: PMC10439182 DOI: 10.1038/s41598-023-40634-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 08/14/2023] [Indexed: 08/20/2023] Open
Abstract
Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful and versatile tool in various scientific fields. These include-among others-imaging, material characterization, and layer thickness measurements. While THz-TDS has achieved significant success in research environments, the high cost and bulky nature of most systems have hindered widespread commercialization of this technology. Two primary factors contributing to the size and cost of these systems are the laser and the optical delay unit (ODU). Consequently, our group has focused on developing THz-TDS systems based on compact monolithic mode-locked laser diodes (MLLDs). The ultra-high repetition rate (UHRR) of the MLLD has the added benefit that it allows us to utilize shorter ODUs, thereby reducing the overall cost and size of our systems. However, achieving the necessary precision in the ODU to acquire accurate terahertz time-domain signals remains a crucial aspect. To address this issue, we have developed and enhanced an interferometric extension for UHRR-THz-TDS systems. This extension is inexpensive, compact, and easy to incorporate. In this article, we present the system setup, the extension itself, and the algorithmic procedure for reconstructing the delay axis based on the interferometric reference signal. We evaluate a dataset comprising 10,000 signal traces and report a standard deviation of the measured terahertz phase at 1.6 THz as low as 3 mrad. Additionally, we demonstrate a remaining peak-to-peak jitter of only 20 fs and a record-high peak signal-to-noise ratio of 133 dB at 100 GHz after averaging. The method presented in this paper allows for simplified THz-TDS system builds, reducing bulk and cost. As a result, it further facilitates the transition of terahertz technologies from laboratory to field applications.
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Affiliation(s)
| | | | | | - Jan C Balzer
- NTS, University of Duisburg Essen, 47057, Duisburg, Germany
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Nakagawa M, Kanda N, Otsu T, Ito I, Kobayashi Y, Matsunaga R. Jitter correction for asynchronous optical sampling terahertz spectroscopy using free-running pulsed lasers. OPTICS EXPRESS 2023; 31:19371-19381. [PMID: 37381353 DOI: 10.1364/oe.488866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 05/16/2023] [Indexed: 06/30/2023]
Abstract
We demonstrate a jitter correction method for asynchronous optical sampling (ASOPS) terahertz (THz) time-domain spectroscopy using two free-running oscillators. This method simultaneously records the THz waveform and a harmonic of the laser repetition rate difference, Δ f r, to monitor the jitter information for software jitter correction. By suppressing the residual jitter below 0.1 ps, the accumulation of the THz waveform is achieved without losing the measurement bandwidth. Our measurement of water vapor successfully resolves the absorption linewidths below 1 GHz, demonstrating a robust ASOPS with a flexible, simple, and compact setup without any feedback control or additional continuous-wave THz source.
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Dai L, Huang Z, Huang Q, Al Araimi M, Rozhin A, Liang X, Mou C. Intracavity-loss controlled wavelength-tunable bidirectional mode-locked erbium-doped fiber laser. OPTICS EXPRESS 2023; 31:8998-9006. [PMID: 36860002 DOI: 10.1364/oe.481788] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Accepted: 01/22/2023] [Indexed: 06/18/2023]
Abstract
Bidirectional wavelength-tunable mode-locked fiber lasers have demands for many applications. In our experiment, two frequency combs from a single bidirectional carbon nanotube mode-locked erbium-doped fiber laser are obtained. Continuous wavelength tuning is demonstrated in the bidirectional ultrafast erbium-doped fiber laser for the first time. We utilized the microfiber assisted differential loss-control effect on both directions to tune operation wavelength and it presents different wavelength tuning performances in two directions. Correspondingly, the repetition rate difference can be tuned from 98.6 Hz to 32 Hz by applying strain on microfiber within 23 µm stretching length. In addition, a minor repetition rate difference variation of 4.5 Hz is achieved. Such technique may provide possibility to expand wavelength range of dual-comb spectroscopy and broad its application fields.
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Li M, Liu Z, Xia Y, He M, Yang K, Yuan S, Yan M, Huang K, Zeng H. Terahertz Time-of-Flight Ranging with Adaptive Clock Asynchronous Optical Sampling. SENSORS (BASEL, SWITZERLAND) 2023; 23:s23020715. [PMID: 36679509 PMCID: PMC9863347 DOI: 10.3390/s23020715] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 12/25/2022] [Accepted: 01/04/2023] [Indexed: 06/12/2023]
Abstract
We propose and implement a terahertz time-of-flight ranging system based on adaptive clock asynchronous optical sampling, where the timing jitter is corrected in real time to recover the depth information in the acquired interferograms after compensating for laser instabilities using electronic signal processing. Consequently, the involved measurement uncertainties caused by the timing jitter during the terahertz sampling process and the noise intensity of the terahertz electric field have been reduced by the utilization of the adaptive clock. The achieved uncertainty range is about 2.5 μm at a 5 cm distance after averaging the acquisition time of 1876 ms 5000 times, showing a significant improvement compared with the asynchronous optical sampling using a constant clock. The implemented terahertz ranging system only uses free-running mode-locked lasers without any phase-locked electronics, and this favors simple and robust operations for subsequent applications that extend beyond the laboratory conditions.
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Affiliation(s)
- Min Li
- Shanghai Key Laboratory of Modern Optical System, Engineering Research Center of Optical Instrument and System, Ministry of Education, School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
| | - Zheng Liu
- Shanghai Key Laboratory of Modern Optical System, Engineering Research Center of Optical Instrument and System, Ministry of Education, School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
| | - Yu Xia
- Shanghai Key Laboratory of Modern Optical System, Engineering Research Center of Optical Instrument and System, Ministry of Education, School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
| | - Mingyang He
- Jinan Institute of Quantum Technology, Jinan 250101, China
| | - Kangwen Yang
- Shanghai Key Laboratory of Modern Optical System, Engineering Research Center of Optical Instrument and System, Ministry of Education, School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
| | - Shuai Yuan
- Shanghai Key Laboratory of Modern Optical System, Engineering Research Center of Optical Instrument and System, Ministry of Education, School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
| | - Ming Yan
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Kun Huang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Heping Zeng
- Shanghai Key Laboratory of Modern Optical System, Engineering Research Center of Optical Instrument and System, Ministry of Education, School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
- Jinan Institute of Quantum Technology, Jinan 250101, China
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
- Chongqing Key Laboratory of Precision Optics, Chongqing Institute of East China Normal University, Chongqing 401121, China
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Bajek D, Cataluna MA. Megahertz scan rates enabled by optical sampling by repetition-rate tuning. Sci Rep 2021; 11:22995. [PMID: 34837019 PMCID: PMC8626425 DOI: 10.1038/s41598-021-02502-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 11/17/2021] [Indexed: 11/09/2022] Open
Abstract
We demonstrate, for the first time, optical sampling by repetition-rate tuning (OSBERT) at record megahertz scan rates. A low-cost, tunable and extremely compact 2-section passively mode-locked laser diode (MLLD) is used as the pulsed laser source, whose repetition rate can be modulated electronically through biasing of the saturable absorber section. The pulsed output is split into two arms comparable to an imbalanced Michelson interferometer, where one arm is significantly longer than the other (a passive delay line, or PDL). The resulting electronic detuning of the repetition rate gives rise to a temporal delay between pulse pairs at a detector; the basis for time-resolved spectroscopy. Through impedance-matching, we developed a new system whereby a sinusoidal electrical bias could be applied to the absorber section of the MLLD via a signal generator, whose frequency could be instantly increased from sub-hertz through to megahertz modulation frequencies, corresponding to a ground-breaking megahertz optical sampling scan rate, which was experimentally demonstrated by the real-time acquisition of a cross-correlation trace of two ultrashort optical pulses within just 1 microsecond of real time. This represents scan rates which are three orders of magnitude greater than the recorded demonstrations of OSBERT to date, and paves the way for highly competitive scan rates across the field of time-resolved spectroscopy and applications therein which range from pump probe spectroscopy to metrology.
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Affiliation(s)
- D Bajek
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - M A Cataluna
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK
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Ultra-High Repetition Rate Terahertz Time-Domain Spectroscopy for Micrometer Layer Thickness Measurement. SENSORS 2021; 21:s21165389. [PMID: 34450830 PMCID: PMC8400559 DOI: 10.3390/s21165389] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Revised: 08/06/2021] [Accepted: 08/07/2021] [Indexed: 11/17/2022]
Abstract
Terahertz time-domain spectroscopy systems driven by monolithic mode-locked laser diodes (MLLDs) exhibit bandwidths exceeding 1 THz and a peak dynamic range that can compete with other state-of-the-art systems. Their main difference compared to fiber-laser-driven systems is their ultra-high repetition rate of typically dozens of GHz. This makes them interesting for applications where the length of the terahertz path may not be precisely known and it enables the use of a very short and potentially fast optical delay unit. However, the phase accuracy of the system is limited by the accuracy with which the delay axes of subsequent measurements are synchronized. In this work, we utilize an all-fiber approach that uses the optical signal from the MLLD in a Mach-Zehnder interferometer to generate a reference signal that we use to synchronize the detected terahertz signals. We demonstrate transmission-mode thickness measurements of stacked layers of 17μm thick low-density polyethylene (LDPE) films.
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