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Spectroscopy|22 Article(s)
High-speed impulsive stimulated Brillouin microscopy|Spotlight on Optics
Jiarui Li, Taoran Le, Hongyuan Zhang, Haoyun Wei, and Yan Li
Brillouin microscopy, which maps the elastic modulus from the frequency shift of scattered light, has evolved to a faster speed for the investigation of rapid biomechanical changes. Impulsive stimulated Brillouin scattering (ISBS) spectroscopy has the potential to speed up measurement through the resonant amplification interaction from pulsed excitation and time-domain continuous detection. However, significant progress has not been achieved due to the limitation in signal-to-noise ratio (SNR) and the corresponding need for excessive averaging to maintain high spectral precision. Moreover, the limited spatial resolution also hinders its application in mechanical imaging. Here, by scrutinizing the SNR model, we design a high-speed ISBS microscope through multi-parameter optimization including phase, reference power, and acquisition time. Leveraging this, with the further assistance of the Matrix Pencil method for data processing, three-dimensional mechanical images are mapped under multiple contrast mechanisms for a millimeter-scale polydimethylsiloxane pattern immersed in methanol, enabling the identification of these two transparent materials without any contact or labeling. Our experimental results demonstrate the capability to maintain high spectral precision and resolution at a sub-millisecond integration time for one pixel. With a two-order improvement in the speed and a tenfold improvement in the spatial resolution over the state-of-the-art systems, this method makes it possible for ISBS microscopes to sensitively investigate rapid mechanical changes in time and space. Brillouin microscopy, which maps the elastic modulus from the frequency shift of scattered light, has evolved to a faster speed for the investigation of rapid biomechanical changes. Impulsive stimulated Brillouin scattering (ISBS) spectroscopy has the potential to speed up measurement through the resonant amplification interaction from pulsed excitation and time-domain continuous detection. However, significant progress has not been achieved due to the limitation in signal-to-noise ratio (SNR) and the corresponding need for excessive averaging to maintain high spectral precision. Moreover, the limited spatial resolution also hinders its application in mechanical imaging. Here, by scrutinizing the SNR model, we design a high-speed ISBS microscope through multi-parameter optimization including phase, reference power, and acquisition time. Leveraging this, with the further assistance of the Matrix Pencil method for data processing, three-dimensional mechanical images are mapped under multiple contrast mechanisms for a millimeter-scale polydimethylsiloxane pattern immersed in methanol, enabling the identification of these two transparent materials without any contact or labeling. Our experimental results demonstrate the capability to maintain high spectral precision and resolution at a sub-millisecond integration time for one pixel. With a two-order improvement in the speed and a tenfold improvement in the spatial resolution over the state-of-the-art systems, this method makes it possible for ISBS microscopes to sensitively investigate rapid mechanical changes in time and space.
Photonics Research
- Publication Date: Mar. 25, 2024
- Vol. 12, Issue 4, 730 (2024)
Frequency-comb-linearized, widely tunable lasers for coherent ranging
Baoqi Shi, Yi-Han Luo, Wei Sun, Yue Hu, Jinbao Long, Xue Bai, Anting Wang, and Junqiu Liu
Tunable lasers, with the ability to continuously vary their emission wavelengths, have found widespread applications across various fields such as biomedical imaging, coherent ranging, optical communications, and spectroscopy. In these applications, a wide chirp range is advantageous for large spectral coverage and high frequency resolution. Besides, the frequency accuracy and precision also depend critically on the chirp linearity of the laser. While extensive efforts have been made on the development of many kinds of frequency-agile, widely tunable, narrow-linewidth lasers, wideband yet precise methods to characterize and linearize laser chirp dynamics are also demanded. Here we present an approach to characterize laser chirp dynamics using an optical frequency comb. The instantaneous laser frequency is tracked over terahertz bandwidth at 1 MHz intervals. Using this approach we calibrate the chirp performance of 12 tunable lasers from Toptica, Santec, New Focus, EXFO, and NKT that are commonly used in fiber optics and integrated photonics. In addition, with acquired knowledge of laser chirp dynamics, we demonstrate a simple frequency-linearization scheme that enables coherent ranging without any optical or electronic linearization unit. Our approach not only presents novel wideband, high-resolution laser spectroscopy, but is also critical for sensing applications with ever-increasing requirements on performance. Tunable lasers, with the ability to continuously vary their emission wavelengths, have found widespread applications across various fields such as biomedical imaging, coherent ranging, optical communications, and spectroscopy. In these applications, a wide chirp range is advantageous for large spectral coverage and high frequency resolution. Besides, the frequency accuracy and precision also depend critically on the chirp linearity of the laser. While extensive efforts have been made on the development of many kinds of frequency-agile, widely tunable, narrow-linewidth lasers, wideband yet precise methods to characterize and linearize laser chirp dynamics are also demanded. Here we present an approach to characterize laser chirp dynamics using an optical frequency comb. The instantaneous laser frequency is tracked over terahertz bandwidth at 1 MHz intervals. Using this approach we calibrate the chirp performance of 12 tunable lasers from Toptica, Santec, New Focus, EXFO, and NKT that are commonly used in fiber optics and integrated photonics. In addition, with acquired knowledge of laser chirp dynamics, we demonstrate a simple frequency-linearization scheme that enables coherent ranging without any optical or electronic linearization unit. Our approach not only presents novel wideband, high-resolution laser spectroscopy, but is also critical for sensing applications with ever-increasing requirements on performance.
Photonics Research
- Publication Date: Mar. 18, 2024
- Vol. 12, Issue 4, 663 (2024)
Dual-comb spectroscopy from the ultraviolet to mid-infrared region based on high-order harmonic generation
Yuanfeng Di, Zhong Zuo, Daowang Peng, Daping Luo, Chenglin Gu, and Wenxue Li
Dual-comb spectroscopy (DCS) has revolutionized numerous spectroscopic applications due to its high spectral resolution and fast measurement speed. Substantial efforts have been made to obtain a coherent dual-comb source at various spectral regions through nonlinear frequency conversion, where the preservation of coherence has become a problem of great importance. In this study, we report the generation of coherent dual-comb sources covering from the ultraviolet to mid-infrared region based on high-order harmonic generation. Driven by high-repetition-rate femtosecond mid-infrared dual-comb pump pulses, up to ninth-order harmonic was generated from the ultraviolet to mid-infrared region using an aperiodically poled lithium niobate waveguide. To investigate the coherence property of the high-order harmonic generation, DCS was performed at every generated spectral region from 450 to 3600 nm. The measured dual-comb spectra with distinctive tooth-resolved structures show the well-preserved coherence without apparent degradation after the cascaded quadratic nonlinear processes. The subsequent methane absorption spectroscopy at multiple spectral regions of different harmonics was carried out to characterize the spectroscopic capability of the system. These results demonstrate the potential of our scheme to generate compact and coherent broadband optical frequency combs for simultaneous multi-target detections. Dual-comb spectroscopy (DCS) has revolutionized numerous spectroscopic applications due to its high spectral resolution and fast measurement speed. Substantial efforts have been made to obtain a coherent dual-comb source at various spectral regions through nonlinear frequency conversion, where the preservation of coherence has become a problem of great importance. In this study, we report the generation of coherent dual-comb sources covering from the ultraviolet to mid-infrared region based on high-order harmonic generation. Driven by high-repetition-rate femtosecond mid-infrared dual-comb pump pulses, up to ninth-order harmonic was generated from the ultraviolet to mid-infrared region using an aperiodically poled lithium niobate waveguide. To investigate the coherence property of the high-order harmonic generation, DCS was performed at every generated spectral region from 450 to 3600 nm. The measured dual-comb spectra with distinctive tooth-resolved structures show the well-preserved coherence without apparent degradation after the cascaded quadratic nonlinear processes. The subsequent methane absorption spectroscopy at multiple spectral regions of different harmonics was carried out to characterize the spectroscopic capability of the system. These results demonstrate the potential of our scheme to generate compact and coherent broadband optical frequency combs for simultaneous multi-target detections.
Photonics Research
- Publication Date: Jun. 30, 2023
- Vol. 11, Issue 7, 1373 (2023)
Recent advances on applications of NV− magnetometry in condensed matter physics
Ying Xu, Weiye Zhang, and Chuanshan Tian
Measuring magnetic response from spin and current is of fundamental interest in condensed matter physics. Negatively charged nitrogen-vacancy (NV-) centers in diamond are emerging as a robust and versatile quantum sensor owing to their high sensitivity, nanometer-scale spatial resolution, and noninvasive operation with access to static and dynamic magnetic and electron transport properties. In this review, we discuss the rapidly growing interest in the implementation of NV- magnetometry to explore condensed matter physics, focusing on three topics: anti/ferromagnetic materials, superconductors, and metals/semimetals/semiconductors. Measuring magnetic response from spin and current is of fundamental interest in condensed matter physics. Negatively charged nitrogen-vacancy (NV-) centers in diamond are emerging as a robust and versatile quantum sensor owing to their high sensitivity, nanometer-scale spatial resolution, and noninvasive operation with access to static and dynamic magnetic and electron transport properties. In this review, we discuss the rapidly growing interest in the implementation of NV- magnetometry to explore condensed matter physics, focusing on three topics: anti/ferromagnetic materials, superconductors, and metals/semimetals/semiconductors.
Photonics Research
- Publication Date: Feb. 27, 2023
- Vol. 11, Issue 3, 393 (2023)
Interpulse stimulation Fourier-transform coherent anti-Stokes Raman spectroscopy
Minjian Lu, Yujia Zhang, Xinyi Chen, Yan Li, and Haoyun Wei
Exploiting the time-resolving ability of ultrafast pulses, Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) stands out among the coherent Raman spectroscopic techniques for providing high-speed vibrational spectra with high spectral resolution, high Raman intensity, and immunity to nonresonant background. However, the impulsive stimulation nature of FT-CARS imposes heavy demands on the laser source and makes it inherently difficult to monitor high-frequency vibrations. Here, a novel FT-CARS strategy to our knowledge based on interpulse stimulation is proposed to provide more flexible measuring wavenumber region and lighten the requirement on ultrafast pulses. The mechanism of this technique is analyzed theoretically, and simulation is performed to show an orders-of-magnitude improvement of Raman intensity in the high-wavenumber region by the method. Experimentally, an ytterbium-doped fiber laser and photonic crystal fiber-based solitons are employed to provide two ∼100-fs pulses as the pump and Stokes, respectively, and to perform interpulse stimulation FT-CARS without sophisticated dispersion control devices. The high-wavenumber region and upper-part fingerprint region measurements are demonstrated as examples of flexible measurement. Combined with other rapid scanning techniques, such as resonant scanners or a dual-comb scheme, this interpulse stimulation FT-CARS promises to make the fascinating FT-CARS available for any desired wavenumber region, covering many more realistic scenarios for biomedical, pathological, and environmental research. Exploiting the time-resolving ability of ultrafast pulses, Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) stands out among the coherent Raman spectroscopic techniques for providing high-speed vibrational spectra with high spectral resolution, high Raman intensity, and immunity to nonresonant background. However, the impulsive stimulation nature of FT-CARS imposes heavy demands on the laser source and makes it inherently difficult to monitor high-frequency vibrations. Here, a novel FT-CARS strategy to our knowledge based on interpulse stimulation is proposed to provide more flexible measuring wavenumber region and lighten the requirement on ultrafast pulses. The mechanism of this technique is analyzed theoretically, and simulation is performed to show an orders-of-magnitude improvement of Raman intensity in the high-wavenumber region by the method. Experimentally, an ytterbium-doped fiber laser and photonic crystal fiber-based solitons are employed to provide two ∼100-fs pulses as the pump and Stokes, respectively, and to perform interpulse stimulation FT-CARS without sophisticated dispersion control devices. The high-wavenumber region and upper-part fingerprint region measurements are demonstrated as examples of flexible measurement. Combined with other rapid scanning techniques, such as resonant scanners or a dual-comb scheme, this interpulse stimulation FT-CARS promises to make the fascinating FT-CARS available for any desired wavenumber region, covering many more realistic scenarios for biomedical, pathological, and environmental research.
Photonics Research
- Publication Date: Feb. 01, 2023
- Vol. 11, Issue 2, 357 (2023)
Gas sensing with 7-decade dynamic range by laser vector spectroscopy combining absorption and dispersion
Xiutao Lou, Yue Wang, Ning Xu, and Yongkang Dong
Laser absorption spectroscopy (LAS) has been widely used for unambiguous detection and accurate quantification of gas species in a diverse range of fields. However, up-to-date LAS-based gas sensors still face challenges in applications where gas concentrations change in a wide range, since it is extremely difficult to balance spectral analysis strategies for different optical thicknesses. Here we present laser vector spectroscopy that combines absorption spectroscopy with dispersion spectroscopy, simultaneously taking advantage of the former’s high sensitivity in the low-concentration region and the latter’s high linearity in the high-concentration region. In the proof-of-concept demonstration of acetylene measurement, it achieves a linear dynamic range of 6×107 (R2>0.9999), which surpasses all other state-of-the-art LAS techniques by more than an order of magnitude, with the capability of highly accurate quantification retained. The proposed laser spectroscopic method paves a novel way of developing large-dynamic-range gas sensors for environmental, medical, and industrial applications. Laser absorption spectroscopy (LAS) has been widely used for unambiguous detection and accurate quantification of gas species in a diverse range of fields. However, up-to-date LAS-based gas sensors still face challenges in applications where gas concentrations change in a wide range, since it is extremely difficult to balance spectral analysis strategies for different optical thicknesses. Here we present laser vector spectroscopy that combines absorption spectroscopy with dispersion spectroscopy, simultaneously taking advantage of the former’s high sensitivity in the low-concentration region and the latter’s high linearity in the high-concentration region. In the proof-of-concept demonstration of acetylene measurement, it achieves a linear dynamic range of 6×107 (R2>0.9999), which surpasses all other state-of-the-art LAS techniques by more than an order of magnitude, with the capability of highly accurate quantification retained. The proposed laser spectroscopic method paves a novel way of developing large-dynamic-range gas sensors for environmental, medical, and industrial applications.
Photonics Research
- Publication Date: Sep. 27, 2023
- Vol. 11, Issue 10, 1687 (2023)
Lamb-dip saturated-absorption cavity ring-down rovibrational molecular spectroscopy in the near-infrared
Roberto Aiello, Valentina Di Sarno, Maria Giulia Delli Santi, Maurizio De Rosa, Iolanda Ricciardi, Giovanni Giusfredi, Paolo De Natale, Luigi Santamaria, and Pasquale Maddaloni
The high-detection-sensitivity saturated-absorption cavity ring-down (SCAR) technique is extended to Lamb-dip spectroscopy of rovibrational molecular transitions in the near-infrared region. Frequency-comb-referenced sub-Doppler saturation measurements, performed on the acetylene (ν1+ν3+ν4←ν4) R(14)e line at 6562 cm-1, are analyzed by a SCAR global line profile fitting routine, based on a specially developed theoretical model. Compared to a conventional cavity ring-down evaluation, our approach yields dip profiles with a linewidth freed from saturation broadening effects, reduced by 40%, and a signal-to-noise ratio increased by 90%. Ultimately, an overall (statistical and systematic) fractional uncertainty as low as 7×10-12 is achieved for the absolute line-center frequency. At the same time, our method is also able to accurately infer the linear (non-saturated) behavior of the gas absorption, providing Lamb-dip-based line strength measurements with a relative uncertainty of 0.5%. The high-detection-sensitivity saturated-absorption cavity ring-down (SCAR) technique is extended to Lamb-dip spectroscopy of rovibrational molecular transitions in the near-infrared region. Frequency-comb-referenced sub-Doppler saturation measurements, performed on the acetylene (ν1+ν3+ν4←ν4) R(14)e line at 6562 cm-1, are analyzed by a SCAR global line profile fitting routine, based on a specially developed theoretical model. Compared to a conventional cavity ring-down evaluation, our approach yields dip profiles with a linewidth freed from saturation broadening effects, reduced by 40%, and a signal-to-noise ratio increased by 90%. Ultimately, an overall (statistical and systematic) fractional uncertainty as low as 7×10-12 is achieved for the absolute line-center frequency. At the same time, our method is also able to accurately infer the linear (non-saturated) behavior of the gas absorption, providing Lamb-dip-based line strength measurements with a relative uncertainty of 0.5%.
Photonics Research
- Publication Date: Jul. 13, 2022
- Vol. 10, Issue 8, 1803 (2022)
Ultrafast photocarrier and coherent phonon dynamics in type-II Dirac semimetal PtTe2 thin films probed by optical spectroscopy
Peng Suo, Shengnan Yan, Ruihua Pu, Wenjie Zhang, Di Li, Jiaming Chen, Jibo Fu, Xian Lin, Feng Miao, Shi-Jun Liang, Weimin Liu, and Guohong Ma
We report the ultrafast photocarrier dynamics and coherent phonon excitation in type-II Dirac semimetal platinum ditelluride (PtTe2) thin films via femtosecond (fs) pump-probe spectroscopy at room temperature. Quantitative analysis revealed that the incoherent electronic relaxation consists of two components: a subpicosecond fast relaxation process and a slow component with a time constant of hundreds of picoseconds (ps). Furthermore, the launch of a coherent acoustic phonon (CAP) in the 20 nm film but absence in the 6.8 nm film uncovers the dominant role of temperature gradient in producing a strain wave. The sound velocity and Young’s modulus in the thick PtTe2 are determined to be 1.736 km/s and 29.5 GPa, respectively. In addition, the coherent optical phonon (COP) with a frequency of 4.7 THz corresponding to Te atoms out-of-plane A1g vibration has been well resolved in all films, which is ascribed to displacive excitation of coherent phonon (DECP). The observation of a strong probe-wavelength dependent COP amplitude reveals the resonant feature of the optical excitation-induced atomic displacement in PtTe2. Our findings provide deep insight into the excitation and dynamics of CAP and COP as well as the photocarriers’ recovery pathway and lifetimes in PtTe2. Our study also demonstrates that the COP spectroscopy is a powerful tool to reveal the modulation of frequency-dependent optical constants induced by atomic vibrations, which may find applications in the fields of optoelectronics and ultrafast photonics. We report the ultrafast photocarrier dynamics and coherent phonon excitation in type-II Dirac semimetal platinum ditelluride (PtTe2) thin films via femtosecond (fs) pump-probe spectroscopy at room temperature. Quantitative analysis revealed that the incoherent electronic relaxation consists of two components: a subpicosecond fast relaxation process and a slow component with a time constant of hundreds of picoseconds (ps). Furthermore, the launch of a coherent acoustic phonon (CAP) in the 20 nm film but absence in the 6.8 nm film uncovers the dominant role of temperature gradient in producing a strain wave. The sound velocity and Young’s modulus in the thick PtTe2 are determined to be 1.736 km/s and 29.5 GPa, respectively. In addition, the coherent optical phonon (COP) with a frequency of 4.7 THz corresponding to Te atoms out-of-plane A1g vibration has been well resolved in all films, which is ascribed to displacive excitation of coherent phonon (DECP). The observation of a strong probe-wavelength dependent COP amplitude reveals the resonant feature of the optical excitation-induced atomic displacement in PtTe2. Our findings provide deep insight into the excitation and dynamics of CAP and COP as well as the photocarriers’ recovery pathway and lifetimes in PtTe2. Our study also demonstrates that the COP spectroscopy is a powerful tool to reveal the modulation of frequency-dependent optical constants induced by atomic vibrations, which may find applications in the fields of optoelectronics and ultrafast photonics.
Photonics Research
- Publication Date: Feb. 17, 2022
- Vol. 10, Issue 3, 03000653 (2022)
Emission spectroscopy of NaYF4:Eu nanorods optically trapped by Fresnel lens fibers
Aashutosh Kumar, Asa Asadollahbaik, Jeongmo Kim, Khalid Lahlil, Simon Thiele, Alois M. Herkommer, Síle Nic Chormaic, Jongwook Kim, Thierry Gacoin, Harald Giessen, and Jochen Fick
NaYF4:Eu nanorods with high aspect ratios are elaborated and optically trapped using dual fiber optical tweezers in a counterpropagating geometry. High trapping efficiency is observed using converging beams, emitted from diffractive Fresnel lenses directly 3D printed onto cleaved fiber facets. Stable nanorod trapping and alignment are reported for a fiber-to-fiber distance of 200 μm and light powers down to 10 mW. Trapping of nanorod clusters containing one to three nanorods and the coupling of nanorod motion in both axial and transverse directions are considered and discussed. The europium emission is studied by polarization-resolved spectroscopy with particular emphasis on the magnetic and electric dipole transitions. The respective σ and π orientations of the different emission lines are determined. The angles with respect to the nanorod axes of the corresponding magnetic and electric dipoles are calculated. Mono-exponential emission decay with decay time of 4–5 ms is reported. It is shown that the nanorod orientation can be determined by purely spectroscopic means. NaYF4:Eu nanorods with high aspect ratios are elaborated and optically trapped using dual fiber optical tweezers in a counterpropagating geometry. High trapping efficiency is observed using converging beams, emitted from diffractive Fresnel lenses directly 3D printed onto cleaved fiber facets. Stable nanorod trapping and alignment are reported for a fiber-to-fiber distance of 200 μm and light powers down to 10 mW. Trapping of nanorod clusters containing one to three nanorods and the coupling of nanorod motion in both axial and transverse directions are considered and discussed. The europium emission is studied by polarization-resolved spectroscopy with particular emphasis on the magnetic and electric dipole transitions. The respective σ and π orientations of the different emission lines are determined. The angles with respect to the nanorod axes of the corresponding magnetic and electric dipoles are calculated. Mono-exponential emission decay with decay time of 4–5 ms is reported. It is shown that the nanorod orientation can be determined by purely spectroscopic means.
Photonics Research
- Publication Date: Jan. 11, 2022
- Vol. 10, Issue 2, 02000332 (2022)
Broadband mid-infrared molecular spectroscopy based on passive coherent optical–optical modulated frequency combs|Editors' Pick
Zhong Zuo, Chenglin Gu, Daowang Peng, Xing Zou, Yuanfeng Di, Lian Zhou, Daping Luo, Yang Liu, and Wenxue Li
Mid-infrared dual-comb spectroscopy is of great interest owing to the strong spectroscopic features of trace gases, biological molecules, and solid matter with higher resolution, accuracy, and acquisition speed. However, the prerequisite of achieving high coherence of optical sources with the use of bulk sophisticated control systems prevents their widespread use in field applications. Here we generate a highly mutually coherent dual mid-infrared comb spectrometer based on the optical–optical modulation of a continuous-wave (CW) interband or quantum cascade laser. Mutual coherence was passively achieved without post-data processes or active carrier envelope phase-locking processes. The center wavelength of the generated mid-infrared frequency combs can be flexibly tuned by adjusting the wavelength of the CW seeds. The parallel detection of multiple molecular species, including C2H2,CH4,H2CO,H2S, COS, and H2O, was achieved. This technique provides a stable and robust dual-comb spectrometer that will find nonlaboratory applications including open-path atmospheric gas sensing, industrial process monitoring, and combustion. Mid-infrared dual-comb spectroscopy is of great interest owing to the strong spectroscopic features of trace gases, biological molecules, and solid matter with higher resolution, accuracy, and acquisition speed. However, the prerequisite of achieving high coherence of optical sources with the use of bulk sophisticated control systems prevents their widespread use in field applications. Here we generate a highly mutually coherent dual mid-infrared comb spectrometer based on the optical–optical modulation of a continuous-wave (CW) interband or quantum cascade laser. Mutual coherence was passively achieved without post-data processes or active carrier envelope phase-locking processes. The center wavelength of the generated mid-infrared frequency combs can be flexibly tuned by adjusting the wavelength of the CW seeds. The parallel detection of multiple molecular species, including C2H2,CH4,H2CO,H2S, COS, and H2O, was achieved. This technique provides a stable and robust dual-comb spectrometer that will find nonlaboratory applications including open-path atmospheric gas sensing, industrial process monitoring, and combustion.
Photonics Research
- Publication Date: Jul. 01, 2021
- Vol. 9, Issue 7, 07001358 (2021)
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