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Yang T, Liu H, Wu F, Chen H, Wang Q, Wei Z, Zhang J. Self-started Kerr-lens mode-locked thin-disk oscillator. OPTICS LETTERS 2023; 48:4633-4636. [PMID: 37656573 DOI: 10.1364/ol.495730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Accepted: 08/04/2023] [Indexed: 09/03/2023]
Abstract
Kerr-lens mode-locking (KLM) has been widely used in thin-disk oscillators to generate high-power femtosecond pulses. Here we demonstrate a Kerr-lens mode-locked Yb:YAG thin-disk oscillator that can be self-started under two configurations. The first can deliver 13-W, 235-fs pulses at a repetition rate of 103 MHz; the second delivers 49 W at a repetition rate of 46.5 MHz, whose corresponding pulse energy of 1.05 µJ is, to the best of our knowledge, the highest energy ever obtained in self-started Kerr-lens mode-locked oscillators. A new method to initiate KLM in the form of optical perturbation in a thin-disk oscillator has also been demonstrated.
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Ponomarev DS, Lavrukhin DV, Glinskiy IA, Yachmenev AE, Zenchenko NV, Khabibullin RA, Goncharov YG, Otsuji T, Zaytsev KI. Enhanced THz radiation through a thick plasmonic electrode grating photoconductive antenna with tight photocarrier confinement. OPTICS LETTERS 2023; 48:1220-1223. [PMID: 36857253 DOI: 10.1364/ol.486431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Accepted: 02/02/2023] [Indexed: 06/18/2023]
Abstract
We propose the design of a photoconductive antenna (PCA) emitter with a plasmonic grating featuring a very high plasmonic Au electrode with a thickness of 170 nm. As we show numerically, the increase in h significantly changes the electric field distribution, owing to the excitation of higher-order plasmon guided modes in the Au slit waveguides, leading to an additional increase in the emitted THz power. We develop the plasmonic grating geometry with respect to maximal transmission of the incident optical light, so as to expect the excitation of higher-order plasmon guided Au modes. The fabricated PCA can efficiently work with low-power laser excitation, demonstrating an overall THz power of 5.3 μW over an ∼4.0 THz bandwidth, corresponding to a conversion efficiency of 0.2%. We believe that our design can be used to meet the demands of modern THz spectroscopic and high-speed imaging applications.
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Chen WC, Chang CW, Yang SH. Group IV THz large area emitter based on GeSn alloy. OPTICS LETTERS 2022; 47:4411-4414. [PMID: 36048666 DOI: 10.1364/ol.464541] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Accepted: 07/31/2022] [Indexed: 06/15/2023]
Abstract
THz photoconductive emitters based on III-V materials have demonstrated excellent THz radiation properties, enabling many unique applications. However, the incompatibility with the complementary-metal-oxide-semiconductor (CMOS) foundry fabrication process and the challenging growth condition hampers THz photoconductive emitters from large-scale production. To address this limitation, we proposed the GeSn alloy as the photoconductive material candidate through the CMOS-compatible epitaxy instrument. The GeSn photoconductor features a 518 cm2/V-s mobility and a 7187 cm-1 absorption coefficient at the wavelength of 1560 nm, resulting in sufficiently ultrafast photocurrent generation for THz radiation. As a result, the GeSn THz emitter provides over a bandwidth of 2 THz and a 40 dB signal-to-noise ratio, which shows its potential in realizing mass-producible, cost-effective THz integrated systems with CMOS technology.
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Chen WC, Yang SH. Thermal evaporated group IV Ge(Sn)-on-Si terahertz photoconductive antenna. OPTICS EXPRESS 2022; 30:31742-31751. [PMID: 36242250 DOI: 10.1364/oe.466108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 08/03/2022] [Indexed: 06/16/2023]
Abstract
We have experimentally demonstrated thermal evaporated group IV Ge1-xSnx-on-Si terahertz (THz) photoconductive antennas (PCA) pumped by an Er-doped femtosecond laser for broadband THz generation. The Ge1-xSnx THz PCAs, free from material epitaxial growth methods, can offer comparable material properties in photocarrier generation, transportation, recombination, and the collection as group III-V THz PCAs. At the optical pumping power of 90 mW and a bias voltage of 40V, the Ge1-xSnx THz PCAs have achieved a broadband spectrum over 1.5 THz with a 40 dB signal-to-noise ratio (SNR). This CMOS-compatible group IV THz source can be monolithically integrated on the Si photonic platform, paving the way toward THz system-on-chip (SoC) for many on-site applications in the non-destructive evaluation, biomedical imaging, and industrial inspections.
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Kohlhaas RB, Breuer S, Mutschall S, Kehrt M, Nellen S, Liebermeister L, Schell M, Globisch B. Ultrabroadband terahertz time-domain spectroscopy using III-V photoconductive membranes on silicon. OPTICS EXPRESS 2022; 30:23896-23908. [PMID: 36225061 DOI: 10.1364/oe.454447] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 04/12/2022] [Indexed: 06/16/2023]
Abstract
Electromagnetic waves in the terahertz (THz) frequency range are widely used in spectroscopy, imaging and sensing. However, commercial, table-top systems covering the entire frequency range from 100 GHz to 10 THz are not available today. Fiber-coupled spectrometers, which employ photoconductive antennas as emitters and receivers, show a bandwidth limited to 6.5 THz and some suffer from spectral artifacts above 4 THz. For these systems, we identify THz absorption in the polar substrate of the photoconductive antenna as the main reason for these limitations. To overcome them, we developed photoconductive membrane (PCM) antennas, which consist of a 1.2 µm-thin InGaAs layer bonded on a Si substrate. These antennas combine efficient THz generation and detection in InGaAs with absorption-free THz transmission through a Si substrate. With these devices, we demonstrate a fiber-coupled THz spectrometer with a total bandwidth of 10 THz and an artifact-free spectrum up to 6 THz. The PCM antennas present a promising path toward fiber-coupled, ultrabroadband THz spectrometers.
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Ponomarev DS, Lavrukhin DV, Zenchenko NV, Frolov TV, Glinskiy IA, Khabibullin RA, Katyba GM, Kurlov VN, Otsuji T, Zaytsev KI. Boosting photoconductive large-area THz emitter via optical light confinement behind a highly refractive sapphire-fiber lens. OPTICS LETTERS 2022; 47:1899-1902. [PMID: 35363764 DOI: 10.1364/ol.452192] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Accepted: 02/16/2022] [Indexed: 05/27/2023]
Abstract
We report on a sapphire-fiber-based lens that can be used to enhance the emitted THz power of a large-area photoconductive antenna (PCA). Using numerical simulations, we demonstrate that the lens provides a spatial redistribution of the photocarriers density in the PCA's gap. By optimizing the diameter of the sapphire-fiber, one could reach efficient confinement of the photocarriers in the vicinity of the PCA electrodes with a 10-μm gap size for a 220-μm-thick sapphire-fiber. This allows enhancing the coupling of the incident electromagnetic waves at the interface between the sapphire fiber and the semiconductor with the antenna terminals by ∼40 times for a single PCA element, as well as boosting the total efficiency of the large-area PCA-emitter up to ∼7-10 times. To validate our approach, we propose a step-by-step process that can be used for the precise and controllable placement of the sapphire-fiber on the surface of a single PCA.
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Optimization of Pixel Size and Electrode Structure for Ge:Ga Terahertz Photoconductive Detectors. SENSORS 2022; 22:s22051916. [PMID: 35271063 PMCID: PMC8914821 DOI: 10.3390/s22051916] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/12/2022] [Revised: 02/12/2022] [Accepted: 02/23/2022] [Indexed: 11/20/2022]
Abstract
To investigate the effects of the pixel sizes and the electrode structures on the performance of Ge-based terahertz (THz) photoconductive detectors, vertical structure Ge:Ga detectors with different structure parameters were fabricated. The characteristics of the detectors were investigated at 4.2 K, including the spectral response, blackbody response (Rbb), dark current density-voltage characters, and noise equivalent power (NEP). The detector with the pixel radius of 400 μm and the top electrode of the ring structure showed the best performance. The spectral response band of this detector was about 20–180 μm. The Rbb of this detector reached as high as 0.92 A/W, and the NEP reached 5.4 × 10−13 W/Hz at 0.5 V. Compared with the detector with a pixel radius of 1000 μm and the top electrode of the spot structure, the Rbb increased nearly six times, and the NEP decreased nearly 12 times. This is due to the fact that the optimized parameters increased the equivalent electric field of the detector. This work provides a route for future research into large-scale array Ge-based THz detectors.
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Li J, Rana R, Zhu L, Liu C, Schneider H, Pashkin A. Limitation of THz conversion efficiency in DSTMS pumped by intense femtosecond pulses. OPTICS EXPRESS 2021; 29:22494-22503. [PMID: 34266011 DOI: 10.1364/oe.423433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 05/26/2021] [Indexed: 06/13/2023]
Abstract
Terahertz (THz) generation via optical rectification (OR) of near-infrared femtosecond pulses in DSTMS is systematically studied using a quasi-3D theoretical model, which takes into account cascaded OR, three-photon absorption (3PA) of the near-infrared radiation, and material dispersion/absorption properties. The simulation results and the comparison with experimental data for pump pulses with the center wavelength of 1.4 µm indicate that the 3PA process is one of the main limiting factors for THz generation in DSTMS at high pump fluences. The THz conversion efficiency is reduced further by the enhanced group velocity dispersion effect caused by the spectral broadening due to the cascaded OR. We predict that for broadband pump pulses with a duration of 30 fs, the THz conversion efficiency can be enhanced by a factor of 1.5 by using a positive pre-chirping that partially suppresses the cascaded OR and the 3PA effects.
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Liebermeister L, Nellen S, Kohlhaas RB, Lauck S, Deumer M, Breuer S, Schell M, Globisch B. Optoelectronic frequency-modulated continuous-wave terahertz spectroscopy with 4 THz bandwidth. Nat Commun 2021; 12:1071. [PMID: 33594078 PMCID: PMC7886886 DOI: 10.1038/s41467-021-21260-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 01/20/2021] [Indexed: 11/09/2022] Open
Abstract
Broadband terahertz spectroscopy enables many promising applications in science and industry alike. However, the complexity of existing terahertz systems has as yet prevented the breakthrough of this technology. In particular, established terahertz time-domain spectroscopy (TDS) schemes rely on complex femtosecond lasers and optical delay lines. Here, we present a method for optoelectronic, frequency-modulated continuous-wave (FMCW) terahertz sensing, which is a powerful tool for broadband spectroscopy and industrial non-destructive testing. In our method, a frequency-swept optical beat signal generates the terahertz field, which is then coherently detected by photomixing, employing a time-delayed copy of the same beat signal. Consequently, the receiver current is inherently phase-modulated without additional modulator. Owing to this technique, our broadband terahertz spectrometer performs (200 Hz measurement rate, or 4 THz bandwidth and 117 dB peak dynamic range with averaging) comparably to state-of-the-art terahertz-TDS systems, yet with significantly reduced complexity. Thickness measurements of multilayer dielectric samples with layer-thicknesses down to 23 µm show its potential for real-world applications. Within only 0.2 s measurement time, an uncertainty of less than 2 % is achieved, the highest accuracy reported with continuous-wave terahertz spectroscopy. Hence, the optoelectronic FMCW approach paves the way towards broadband and compact terahertz spectrometers that combine fiber optics and photonic integration technologies. Time-domain spectroscopy with terahertz frequencies typically requires complex and bulky systems. Here, the authors present an opto-electronics-based, frequency-domain terahertz sensing technique which offers competitive measurement performance in a much simpler system.
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Affiliation(s)
- Lars Liebermeister
- Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Berlin, Germany.
| | - Simon Nellen
- Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Berlin, Germany
| | - Robert B Kohlhaas
- Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Berlin, Germany
| | - Sebastian Lauck
- Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Berlin, Germany
| | - Milan Deumer
- Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Berlin, Germany
| | - Steffen Breuer
- Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Berlin, Germany
| | - Martin Schell
- Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Berlin, Germany.,Institut für Festkörperphysik, Technische Universität Berlin, Berlin, Germany
| | - Björn Globisch
- Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Berlin, Germany.,Institut für Festkörperphysik, Technische Universität Berlin, Berlin, Germany
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