Probe Beam Research Articles

Comment on "Frequency-domain probe beam deflection method for measurement of thermal conductivity of materials on micron length scale" [Rev. Sci. Instrum. 94, 014903 (2023)

Comment on "Frequency-domain probe beam deflection method for measurement of thermal conductivity of materials on micron length scale" [Rev. Sci. Instrum. 94, 014903 (2023)

Response to "Comment on 'Frequency-domain probe beam deflection method for measurement of thermal conductivity of materials on micron length scale'" [Rev. Sci. Instrum. 95, 067101 (2024)

Response to "Comment on 'Frequency-domain probe beam deflection method for measurement of thermal conductivity of materials on micron length scale'" [Rev. Sci. Instrum. 95, 067101 (2024)

Analyzing coherent and incoherent optical susceptibilities in four-wave mixing: stochasticity, symmetry, and intramolecular coupling

The nonlinear optical susceptibilities are analyzed in their optical propagation length considering the incoherent-coherent contributions with the dependence on the relaxation times. In addition, some symmetry properties of the Four-Wave mixing (FWM) signal concerning the frequency detuning exchange are used in the study, without restricting ourselves to the maxima of population oscillations. We analyze the behaviors of these optical responses in a vibronic coupling scheme using a molecule model consisting of two coupled harmonic curves of electronic energies with displaced minima in position and nuclear energies. The solvent effect in our model is treated through the natural Bohr frequency shift to a time-dependent function, with explicit manifestations in its comparison as if the upper state were broadened. Our results for both FWM signal propagation and nonlinear optical susceptibilities are sensitive to the intramolecular coupling parameters, solvent stochasticity, and perturbation order for the treatment of the weak probe beam. The consideration of a second-order probe beam in FWM would not represent a significant contribution to the predicted results, since its percentage contribution is negligible within the model development framework; however, this contribution becomes important when increasing the ratio between longitudinal and transverse relaxation times.

Photon counting based pump-probe technique for quantitative characterization of fluorescence in a lock-in free detection manner

The stimulated emission (SE) signal in pump-probe experiment is conventionally measured with lock-in detection to differentiate the weak signals from the relatively large background of spontaneous emission and probe beam. Therefore, direct characterization of signal strength are often major limiting factors in terms of noise, speed, and data acquisition. In contrast, photon counting allows direct quantification of signal strength, while synchronized pump-probe pulse enables precise timing and the separation of signals accordingly. Herein, the SE based pump-probe method is combined with time-correlated single-photon counting to investigate the ultrafast photochemical parameters, digitally and quantitatively. As a proof-of-concept, our technique is applied to investigate, fluorescence lifetime (τ)∼3.71ns , optical absorption cross-section (σabs)∼1.23×10−16cm2 , and the SE cross-section (σSE)∼2.22×10−17cm2 , of a fluorescent dye (ATTO 647N) quantitatively. The experimental results are also compared with theoretical photon statistics to further justify the advantages including experimental and statistical critical molecular dynamics parameters extraction with excellent high accuracy.

Optical storage of circular airy beam in atomic vapor

Abstract The realization of quantum storage of spatial light field is of great significance to the construction of high-dimensional quantum repeater. In this paper, we experimentally realize the storage and retrieval of circular Airy beams (CABs) by using the Λ-type three-level energy system based on the electromagnetically induced transparency in a hot rubidium atomic vapor cell. The weak probe beam field is modulated with phase distribution of CABs by a spatial light modulator. We store the probe circular Airy beam (CAB) into the rubidium atomic vapor cell and retrieve it after the demanded delay. We quantitatively analyze the storage results and give corresponding theoretical explanations. Moreover, we investigate the autofocusing and self-healing effect of the retrieved CAB, which indicates that the properties and beam shape of CAB maintain well after storage. Our work will have potential applications in the storage of high-dimensional quantum information, and is also useful for improving the channel capacities of quantum internet.

On the perturbation of the interferometric phase in interferometry-polarimetry of fusion plasmas

The perturbation of the interferometric phase is a corrective term of the measured phase shift that should be taken into account in the measurement of the electron line density in a combined interferometer-polarimeter for the diagnostics of the electron density and the magnetic field in a fusion plasma. In this paper we first review in detail the theory of this effect and present a new and complete derivation of it, which also accounts for some errors published in a previous paper. Then we consider this effect in the interferometer-polarimeter of three different plasma devices: RTP, JET and DTT and for each machine we calculate the expected phase perturbation for a typical plasma profile, especially with reference to the use of the popular three-wave technique for the polarization modulation of the input probing beam.

Optimize Electron Beam Energy toward In Situ Imaging of Thick Frozen Bio-Samples with Nanometer Resolution Using MeV-STEM.

To optimize electron energy for in situ imaging of large biological samples up to 10 μm in thickness with nanoscale resolutions, we implemented an analytical model based on elastic and inelastic characteristic angles. This model has been benchmarked by Monte Carlo simulations and can be used to predict the transverse beam size broadening as a function of electron energy while the probe beam traverses through the sample. As a result, the optimal choice of the electron beam energy can be realized. In addition, the impact of the dose-limited resolution was analysed. While the sample thickness is less than 10 μm, there exists an optimal electron beam energy below 10 MeV regarding a specific sample thickness. However, for samples thicker than 10 μm, the optimal beam energy is 10 MeV or higher depending on the sample thickness, and the ultimate resolution could become worse with the increase in the sample thickness. Moreover, a MeV-STEM column based on a two-stage lens system can be applied to reduce the beam size from one micron at aperture to one nanometre at the sample with the energy tuning range from 3 to 10 MeV. In conjunction with the state-of-the-art ultralow emittance electron source that we recently implemented, the maximum size of an electron beam when it traverses through an up to 10 μm thick bio-sample can be kept less than 10 nm. This is a critical step toward the in situ imaging of large, thick biological samples with nanometer resolution.

Comparison of Gaussian and vortex probe beams for deep-learning-based turbulence correction

Optical transmission through atmospheric turbulence is a critical issue for establishing optical communication based on photonic spatial degrees of freedom. Refractive index fluctuations by a turbulent atmosphere cause structural distortion on the transmitted laser beams, resulting in crosstalk between adjacent spatial modes. We study a deep-learning technique to compensate for the turbulence effect. In particular, we mainly focus on improving the correction performance according to the selection of a probe beam. Different modes of Laguerre-Gaussian beams, including the lowest order (Gaussian), are employed as optical probes, and their abilities to compensate for turbulence effects are compared. Our results show that the Gaussian probe beam achieves a higher average correlation coefficient and a lower error rate, i.e., better correction performance, despite the spot size smaller than higher-order modes. Finally, to demonstrate the origin of the performance difference, we examine residual phases by spatial position and discuss the correction coverages.

Morphometric evaluation of mitochondrial networks in regenerating myofibers using photothermal microscopy

Background: Mitochondria constitute their interconnected network through dynamic mitochondrial processes such as fission and fusion in response to changes in their intracellular environment, such as energy demand. Transmission electron microscopy is the standard method for evaluating mitochondrial morphology. We have developed a simple method to evaluate mitochondrial morphology using tissue sections for bright-field observation. In this study, we attempted to image light-absorbing molecules (cytochrome c) in mitochondria using photothermal (PT) microscopy. Purpose: This method can observe an entire myocyte, so this study attempted to evaluate the entire mitochondrial network of immature (regenerating) myocytes during the skeletal muscle regeneration process. Methods: The gastrocnemius muscle of anesthetized male Wistar rats (13 weeks old) was subjected to 300 controlled eccentric contractions (ECC) using electrical stimulation. 7 days after ECC loading, in situ perfusion fixation was performed, and transverse sections (1 μm) from red (deep regions) and white (superficial regions) were prepared after Epon embedding. The sections were observed by PT microscopy, and quantitative analysis of mitochondrial morphology was performed. Mitochondrial content was expressed as a percentage of the fiber total area in transverse sections. The PT imaging system uses lasers with wavelengths of 515 nm and 638 nm constituting the PT pump and the probe beams, respectively. Results: After 7 days of ECC, many myofibers with small fiber diameters and central nuclei, which are characteristic of the recovery process after muscle damage, were observed. The cross-sectional area of the regenerating muscle (superficial region 389.9 ± 15.2 μm2, deep region 366.2 ± 17.5 μm2) was significantly smaller than that of the normal muscle (superficial region 2211.1 ± 127.3 μm2, deep region 1396.1 ± 72.9 μm2). Mitochondrial content of the regenerating muscle (superficial region 26.1 ± 1.1%, deep region 22.7 ± 0.8%) was significantly lower than that of the normal muscle (superficial region 31.8 ± 1.9%, deep region 34.9 ± 1.8%). In normal muscle, a linear network of mitochondria along myofibrils was observed. On the other hand, no spatially distributed mitochondria were observed in the cytoplasm of the regenerating muscle. Furthermore, a mitochondrial network was formed around the periphery of the central nucleus. Conclusion: In muscle tissue imaging using PT microscopy, myofibers in the regenerative process have less mitochondrial content than mature muscle fibers and lack the mitochondrial network along myofibrils that characterizes mature muscle. On the other hand, the central nucleus of immature muscle was surrounded by highly developed mitochondria. The mitochondrial morphological characteristics of regenerating muscle fibers may offer a unique window through which to better understand mitochondrial design and function and their plasticity during maturation. This study was supported in part by a Grant-in-Aid for Japan Society for the Promotion of Science (JSPS) KAKENHI Grant (No. JP20H04074, 21K19703). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Data-volume reduction of optical vortex laser absorption spectroscopy by coarse-graining using a quadrant photodiode

We developed optical vortex laser absorption spectroscopy (OVLAS) to measure the transverse flow velocity relative to the probe beam. In our previous OVLAS setups, a camera is used in the measurement system. This approach constrained the time resolution by image data transfer time and required large computational resources due to the considerable amount of image data. In this paper, we discuss the coarse-graining of OVLAS as a method to improve time resolution and reduce computational resources achieved by replacing the camera with a quadrant photodiode (QPD). Measurement image data obtained from a camera was numerically coarse-grained to evaluate the feasibility of measurements using a QPD. Subsequently, the transverse flow velocity was measured by QPD. Measured transverse flow velocity had a mean absolute percentage error of 18%, confirming the practical validity of coarse-graining OVLAS. The data volume required to determine the flow velocity was reduced to 1/120 from the original OVLAS.

Brillouin frequency shift measurement by zero-crossing point search in virtually synthesized spectra of Brillouin gain and loss

We demonstrate a method for fast and precise Brillouin frequency shift measurement based on searching for the zero-crossing point of a virtually composed spectrum of Brillouin gain and loss obtained by a dual-frequency probe beam. Simulations and experiments show that searching for the zero-crossing point of a virtually synthesized Brillouin gain spectrum can be easily done without a large error compared with peak search of the Brillouin gain spectrum in the conventional method.

Optical gain in a degenerate two-level system in the presence of a transverse magnetic field

Here we report a theoretical model that allows magnetically assisted narrowband probe beam amplification in a closed two-level system with triple Zeeman degeneracy. The gain mechanism can be understood in terms of coherent population transfer between the levels of the Zeeman ground state induced by the external magnetic field. The theoretical model we develop here using a simpler atomic transition Fg=1→Fe=0, in agreement with the experimental results already observed in recent literature. Additionally, we validate our theoretical predictions with the results obtained via density matrix numeric calculation and we believe our theoretical results could useful in communication protocols involving distant nodes.

Dual-Criteria Decision Analysis by Multiphotonic Effects in Nanostructured ZnO.

Simultaneous interrogation of pump and probe beams interacting in ZnO nanostructures of a two-wave mixing is proposed for dual-path data processing of optical signals by nonlinear optical effects. An enhancement in third-order nonlinear optical properties was exhibited by Al-doped ZnO thin films. Multiphoton absorption and nonlinear refraction were explored by the z-scan technique at 532 nm with nanosecond pulses. The evolution of the optical Kerr effect in the ZnO thin films was analyzed as a function of the incorporation of Al in the sample by a vectorial two-wave mixing method. Electrical and photoconductive effects were evaluated to further characterize the influence of Al in the ZnO solid samples. Potential applications of nonlinear optical parameters for encoding and encrypting information in light can be envisioned.

Noncollinear electro-optic detection of terahertz waves: Advantages and limitations

Electro-optic sampling of terahertz waves by noncollinearly propagating femtosecond laser pulses in electro-optic crystals can provide high efficiency and high spectral resolution of terahertz detection with various types of crystals and laser wavelengths, unlike the conventional collinear scheme. We develop an analytical theory of noncollinear electro-optic sampling detection technique that describes the modulation of the probe laser beam polarization as a result of nonlinear interaction between the optical and terahertz fields. The theory accounts for finite widths of the terahertz and probe beams. It is found that noncollinear scheme operates as a low-pass terahertz filter with the frequency cut-off determined by the width of the probe beam and the crossing angle of the terahertz and probe beams. We apply the theory to two practical situations: sampling of terahertz waves by fiber laser pulses (1.55 μm wavelength) in a GaAs crystal and sampling by Ti:sapphire laser pulses (800 nm wavelength) in a LiNbO3 crystal.

Experimental demonstration of complex four-wave mixing processes with pump of orbital-angular-momentum superposition mode

Orbital angular momentum (OAM), characterized by a topological charge ℓ (ℓ integer), serves as a promising vehicle for carrying quantum information. Generating a nonclassical field involving two or more OAM modes can largely enhance the data-carrying capacity of quantum information processing. In this Letter, we present the implementation of a four-wave mixing (FWM) process, featuring a pump beam of a coherent OAM superposition mode and a probe beam of a single OAM mode. We generate twin beams encompassing multiple OAM modes and illustrate their quantum correlation when the pump beam assumes different coherent OAM superposition modes. Furthermore, we analyze the OAM mode components in each output field to deepen our understanding of the nonlinear interaction among different OAM modes. The obtained results show the rich structure of the nonlinear interaction of OAM modes in the FWM process and provide a perspective to study quantum information protocols.

Ultrabroadband two-dimensional electronic spectroscopy in the pump-probe geometry using conventional optics.

We report ultrabroadband two-dimensional electronic spectroscopy (2D ES) measurements obtained in the pump-probe geometry using conventional optics. A phase-stabilized Michelson interferometer provides the pump-pulse delay interval, τ1, necessary to obtain the excitation-frequency dimension. Spectral resolution of the probe beam provides the detection-frequency dimension, ω3. The interferometer incorporates active phase stabilization via a piezo stage and feedback from interference of a continuous-wave reference laser detected in quadrature. To demonstrate the method, we measured a well-characterized laser dye sample and obtained the known peak structure. The vibronic peaks are modulated as a function of the waiting time, τ2, by vibrational wave packets. The interferometer simplifies ultrabroadband 2D ES measurements and analysis.

Balanced-detection interferometric cavity-assisted photothermal spectroscopy via collimating fiber-array integration

This work reports on the implementation of a fiber-array with attached microlenses in the balanced-detection Interferometric Cavity-Assisted Photothermal Spectroscopy (ICAPS) scheme, enabling a highly compact probe laser beam path. The sample probe and the reference beam were coupled into a 1-mm spaced Fabry-Perot interferometer with a parallel beam separation of only 1.25 mm. A quantum cascade laser was used to induce photothermal waves, which were detected via a sample probe beam. A reference probe beam was used to realize balanced detection, allowing for significant noise reduction. The sensor’s metrological figures of merit were evaluated by detection of nitric oxide. For the targeted absorption band centered at 1900.08 cm−1 a 1 σ minimum detection limit of 64 ppbv was achieved with a 1-second integration time. This performance corresponds to a normalized noise equivalent absorption of 5.7 ×10−8 cm−1 W Hz−1/2.

Multichannel Doppler fiber-imager spectrometer for spatiotemporal characterization of high-intensity laser-driven plasmas.

We demonstrate a flexible multichannel fiber-based imaging Doppler spectrometer to characterize plasmas in high intensity (≥1 × 1018 W/cm2) laser-plasma experiments at high repetition rates. This instrument collects data from ×21 different plasma locations combining optical fibers and a single imaging spectrometer. This diagnostic maps the plasma velocity evolution as a function of time with sub-pico-second resolution. Experimental results showing 2D velocity measurements of plasma with 20 μm spatial resolution are presented. Intensities of the order of 1018 W/cm2 were used to generate a plasma, while a much less intense, frequency doubled (400nm), probe beam (1011 W/cm2) was used to measure the Doppler shift from the plasma critical surface. The instrument can be scaled to a larger number of channels (e.g., 100) still using a single spectrometer.

Broadband heterodyne electro-optic sampling using a lithium niobate ridge-waveguide

Abstract We demonstrated the bandwidth broadening of terahertz waves detected by heterodyne electro-optical sampling by implementing a ridge waveguide structure in a lithium niobate (LiNbO3) crystal. Such an approach effectively reduces absorption loss, eases the phase matching condition and enhances the nonlinear interaction length through the optical confinement effect. As a result, we have more than doubled the bandwidth and improved the signal-to-noise ratio compared with an equivalent approach in a bulk LiNbO3 crystal. Heterodyne electro-optic sampling in a ridged-waveguide structure is only marginally dependent on the probe beam wavelength, suggesting its potential as a versatile method for broadband terahertz detection.

Modeling and correction of image drift in dynamic shadowgraphy experiments

The study of phoretic transport phenomena under non-stationary conditions presents several challenges, mostly related to the stability of the experimental apparatus. This is particularly true when investigating with optical means the subtle temperature and concentration fluctuations that arise during diffusion processes, superimposed to the macroscopic state of the system. Under these conditions, the tenuous signal from fluctuations is easily altered by the presence of artifacts. Here, we address an experimental issue frequently reported in the investigation by means of dynamic shadowgraphy of the non-equilibrium fluctuations arising in liquid mixtures under non-stationary conditions, such as those arising after the imposition or removal of a thermal stress, where experiments show systematically the presence of a spurious contribution in the reconstructed structure function of the fluctuations, which depends quadratically from the time delay. We clarify the mechanisms responsible for this artifact, showing that it is caused by the imperfect alignment of the sample cell with respect to gravity, which couples the temporal evolution of the concentration profile within the sample with the optical signal collected by the shadowgraph diagnostics. We propose a data analysis protocol that enables disentangling the spurious contributions and the genuine dynamics of the fluctuations, which can be thus reliably reconstructed.Graphic The imposition of a thermal gradient across a liquid mixture results in a time-dependent refractive index distribution. In the presence of a misalignment of the confining cell with respect to gravity, this leads to a deflection of the optical probe beam used to monitor concentration fluctuations within the sample in quantitative shadowgraphy experiments. If not properly accounted for, this effect can introduce a significant bias in the optical signal.