Strong Laser Light Research Articles

The Fundamental of Fiber Bragg Grating (FBG) Sensor

An optical sensor known as an FBG is produced by laterally exposing a single mode fiber core to a strong UV laser light pattern on a regular basis. The exposure causes a sustained increase in the refractive index (ncore) of the fiber's core, resulting in fixed index modulation called grating (λ). The grating inside the fiber optic core must reflect a certain wavelength of incoming light while transmitting all other wavelengths. This wavelength is referred to as the Bragg wavelength or Bragg linked to grating period. FBG functions as intended when a Bragg reflector is built on an optical fiber by taking use of the regular fluctuations in the refractive index of the single mode fiber core. When light travels through the FBG, certain wavelengths will be transmitted and others will be reflected. When the strain or temperature around the grating varies, a shift in the wavelength of the light reflected is observed.

First-principles screening of metal–organic frameworks for entangled photon pair generation

The transmission of strong laser light in nonlinear optical materials can generate output photons sources that carry quantum entanglement in multiple degrees of freedom, making this process a fundamentally important tool in optical quantum technology. However, the availability of efficient optical crystals for entangled light generation is severely limited in terms of diversity, thus reducing the prospects for the implementation of next-generation protocols in quantum sensing, communication and computing. To overcome this, we developed and implemented a multi-scale first-principles modeling technique for the computational discovery of novel nonlinear optical devices based on metal–organic framework (MOF) materials that can efficiently generate entangled light via spontaneous parametric down-conversion (SPDC). Using collinear degenerate type-I SPDC as a case study, we computationally screen a database of 114 373 synthesized MOF materials to establish correlations between the structure and chemical composition of MOFs with the brightness and coherence properties of entangled photon pairs. We identify a subset of 49 non-centrosymmetric mono-ligand MOF crystals with high chemical and optical stability that produce entangled photon pairs with intrinsic G(2) correlation times τc∼10−30 fs and pair generation rates in the range 104−1010s−1mW−1mm−1 at 1064 nm. Conditions for optimal type-I phase matching are given for each MOF and relationships between pair brightness, crystal band gap and optical birefringence are discussed. Correlations between the optical properties of crystals and their constituent molecular ligands are also given. Our work paves the way for the computational design of MOF-based devices for optical quantum technology.

3D sympathetic cooling and detection of levitated nanoparticles

Cooling the center-of-mass motion of levitated nanoparticles provides a route to quantum experiments at mesoscopic scales. Here we demonstrate three-dimensional sympathetic cooling and detection of the center-of-mass motion of a levitated silica nanoparticle. The nanoparticle is electrostatically coupled to a feedback-cooled particle while both particles are trapped in the same Paul trap. We identify two regimes, based on the strength of the cooling: in the first regime, the sympathetically cooled particle thermalizes with the directly cooled one, while in the second regime, the sympathetically cooled particle reaches a minimum temperature. This result provides a route to efficiently cool and detect particles that cannot be illuminated with strong laser light, such as absorptive particles, and paves the way for controlling the motion of arrays of several trapped nanoparticles.

Phasor Analysis Reveals Multicomponent Fluorescence Kinetics in the LH2 Complex from Marichromatium purpuratum.

We investigated the fluorescence kinetics of LH2 complexes from Marichromatium purpuratum, the cryo-EM structure of which has been recently elucidated with 2.4 Å resolution. The experiments have been carried out as a function of the excitation density by varying both the excitation fluence and the repetition rate of the laser excitation. Instead of the usual multiexponential fitting procedure, we applied the less common phasor formalism for evaluating the transients because this allows for a model-free analysis of the data without a priori knowledge about the number of processes that contribute to a particular decay. For the various excitation conditions, this analysis reproduces consistently three lifetime components with decay times below 100 ps, 500 ps, and 730 ps, which were associated with the quenched state, singlet-triplet annihilation, and fluorescence decay, respectively. Moreover, it reveals that the number of decay components that contribute to the transients depends on whether the excitation wavelength is in resonance with the B800 BChl a molecules or with the carotenoids. Based on the mutual arrangement of the chromophores in their binding pockets, this leads us to conclude that the energy transfer pathways within the LH2 complex of this species differ significantly from each other for exciting either the B800 BChl molecules or the carotenoids. Finally, we speculate whether the illumination with strong laser light converts the LH2 complexes studied here into a quenched conformation that might be related to the development of the non-photochemical quenching mechanism that occurs in higher plants.

A new view of trapping pressure estimation using PVT simulation of hydrocarbon inclusions in petroliferous basins

The trapping pressure of hydrocarbon inclusions can provide important information for fluid analysis in petroliferous basins. It can be obtained through PVT (pressure-volume-temperature) simulation, in which the gaseous filling degree (FV) of the hydrocarbon inclusion is a key parameter. Although it is believed that FV can significantly influence trapping pressure calculations, few studies have provided detailed numerical evidence. Here, we conducted a series of numerical experiments using thermodynamic simulation software to unravel the relationship between FV and trapping pressure. The results indicate that the influence is negligible when FV exceeds a certain value, while the FV can greatly influence trapping pressure when it is less than the certain value, especially a very low one. In addition, we discussed problems existing in the volumetric calculation of hydrocarbon inclusions based on Confocal Laser Scanning Microscopy, which is the predominant method. We find that a vapour bubble shrinks in the lateral plane and is stretched along the vertical axis under relatively strong monochromic or laser light, which is thought to be due to light pressure. Therefore, the vapour bubble can be regarded as a cylinder when it is restricted vertically due to the thin thickness of the inclusion, or an elongated ellipsoid when the inclusion is much thicker than it. Certain errors may be diminished or eliminated theoretically. Case studies are used to validate this novel approach. This view will help to improve the PVT simulation method and even develop new programs.

Research progress of low-dimensional semiconductor materials in field of nonlinear optics

Since the first ruby laser was invented, researchers have focused their attention on how to achieve a strong laser light source, which cannot be produced by the ordinary light sources. Since then, the rich and colorful characteristics of nonlinear optical materials have been discovered, such as the saturation absorption, reverse saturation absorption and nonlinear refraction. They are applied to optoelectronic devices, optical switching devices and optical communication. At the same time, with the increase of the requirements for device integration performance in industrial production, ordinary three-dimensional devices are difficult to meet the production requirements, and the advent of low-dimensional semiconductor devices effectively solves this problem. Therefore, the combination of nonlinear optics and low-dimensional semiconductor materials is a general trend. The emergence of quantum dots, quantum wire lasers, and amplifiers confirms this. In this paper, we summarize the frontier work on nonlinear optics by selecting several special low-dimensional structures and several materials, providing some references for future research. However, due to the fact that the instability and low filling ratio of low-dimensional materials remain to be improved, further relevant research is still required.

Hybrid Modeling Approaches to Study Structures and Dynamics of Biological Systems

Determination of the structure and dynamics of large biological complexes can be performed using experimental techniques ranging from high to low-resolution. With recent progress in experimental techniques, raw data from Cryo Electron Microscopy (cryo-EM) may now comprise millions of two-dimensional (2D) images of single molecules. These may represent distinct conformations of the molecule; therefore, dynamics information might also be embedded within the 2D data. X-ray free electron laser (XFEL) is another exciting new technology that could significantly extend our structural knowledge of biological systems. Strong laser light from XFEL enables the measurement of single molecular complex, without necessity of crystallization. However, for biological systems, due to their low diffraction power, interpretation of the data remains challenging. Given progresses in experimental techniques, new computational methods are needed to process and interpret data obtained from these single particle experiments. We will discuss hybrid computational methods that combine molecular mechanics and image data processing algorithms to derive structural and dynamical information from cryo-EM and XFEL data.

Ultrathin Self-Assembled Diphenylalanine Nanosheets through a Gold-Stabilized Strategy for High-Efficiency Adsorption/Desorption/Ionization.

Herein, the ultrathin and robust diphenylalanine (FF) self-assembled nanosheets were fabricated by a gold-stabilized strategy for the first time, using a facile electrospray method followed by a thermal treatment process. The key for the gold-stabilized mechanism was explored, demonstrating that the synergy of the stable binding and steric effect between gold nanoparticles (AuNPs) and the exposed amino groups of FF nanosheets, led to strong thermal stability and solvent resistance of the composites. Contributing to the features of remarkable accessible surfaces and strong laser light absorption ability of this FF/Au nanosheets, two robust functional devices, that is, solid-phase microextraction (SPME) fiber and surface-assisted laser desorption/ionization (SALDI) platforms, were in situ prepared for in vitro and in vivo biological analysis. The findings indicated that the fabricated platforms possessed two advantages: (1) rapid absorption/desorption speed (within 5 min) and (2) remarkable enhancement of ionization efficiency with 2 orders of magnitude. As a result, the extraction efficiency of the SPME fiber and the quantitation ability of SALDI platform were significantly improved. This study not only demonstrated that FF/Au composites could be prepared through an electrospray method followed with thermal-treatment to serve as promising adsorption/desorption/ionization materials for specific applications but also provided useful strategy to advance the ideas for future combination of SPME with LDI technique.

Strong laser field control of fragment spatial distributions from a photodissociation reaction

The notion that strong laser light can intervene and modify the dynamical processes of matter has been demonstrated and exploited both in gas and condensed phases. The central objective of laser control schemes has been the modification of branching ratios in chemical processes, under the philosophy that conveniently tailored light can steer the dynamics of a chemical mechanism towards desired targets. Less explored is the role that strong laser control can play on chemical stereodynamics, i.e. the angular distribution of the products of a chemical reaction in space. This work demonstrates for the case of methyl iodide that when a molecular bond breaking process takes place in the presence of an intense infrared laser field, its stereodynamics is profoundly affected, and that the intensity of this laser field can be used as an external knob to control it.

Cavity Femtochemistry: Manipulating Nonadiabatic Dynamics at Avoided Crossings.

Molecular potential energy surfaces can be actively manipulated by light. This is usually done by strong classical laser light but was recently demonstrated for the quantum field in an optical cavity. The photonic vacuum state of a localized cavity mode can be strongly mixed with the molecular degrees of freedom to create hybrid field-matter states known as polaritons. We simulate the avoided crossing of sodium iodide in a cavity by incorporating the quantized cavity field into the nuclear wave packet dynamics calculation. The quantized field is represented on a numerical grid in quadrature space, thus avoiding the limitations set by the rotating wave approximation (RWA) when the field is expanded in Fock space. This approach allows the investigation of cavity couplings in the vicinity of naturally occurring avoided crossings and conical intersections, which is too expensive in the fock space expansion when the RWA does not apply. Numerical results show how the branching ratio between the covalent and ionic dissociation channels can be strongly manipulated by the optical cavity.

Profiles of second- to fourth-order moments of turbulent temperature fluctuations in the convective boundary layer: first measurements with rotational Raman lidar

Abstract. The rotational Raman lidar (RRL) of the University of Hohenheim (UHOH) measures atmospheric temperature profiles with high resolution (10 s, 109 m). The data contain low-noise errors even in daytime due to the use of strong UV laser light (355 nm, 10 W, 50 Hz) and a very efficient interference-filter-based polychromator. In this paper, the first profiling of the second- to fourth-order moments of turbulent temperature fluctuations is presented. Furthermore, skewness profiles and kurtosis profiles in the convective planetary boundary layer (CBL) including the interfacial layer (IL) are discussed. The results demonstrate that the UHOH RRL resolves the vertical structure of these moments. The data set which is used for this case study was collected in western Germany (50°53'50.56'' N, 6°27'50.39'' E; 110 m a.s.l.) on 24 April 2013 during the Intensive Observations Period (IOP) 6 of the HD(CP)2 (High-Definition Clouds and Precipitation for advancing Climate Prediction) Observational Prototype Experiment (HOPE). We used the data between 11:00 and 12:00 UTC corresponding to 1 h around local noon (the highest position of the Sun was at 11:33 UTC). First, we investigated profiles of the total noise error of the temperature measurements and compared them with estimates of the temperature measurement uncertainty due to shot noise derived with Poisson statistics. The comparison confirms that the major contribution to the total statistical uncertainty of the temperature measurements originates from shot noise. The total statistical uncertainty of a 20 min temperature measurement is lower than 0.1 K up to 1050 m a.g.l. (above ground level) at noontime; even for single 10 s temperature profiles, it is smaller than 1 K up to 1020 m a.g.l. Autocovariance and spectral analyses of the atmospheric temperature fluctuations confirm that a temporal resolution of 10 s was sufficient to resolve the turbulence down to the inertial subrange. This is also indicated by the integral scale of the temperature fluctuations which had a mean value of about 80 s in the CBL with a tendency to decrease to smaller values towards the CBL top. Analyses of profiles of the second-, third-, and fourth-order moments show that all moments had peak values in the IL around the mean top of the CBL which was located at 1230 m a.g.l. The maximum of the variance profile in the IL was 0.39 K2 with 0.07 and 0.11 K2 for the sampling error and noise error, respectively. The third-order moment (TOM) was not significantly different from zero in the CBL but showed a negative peak in the IL with a minimum of −0.93 K3 and values of 0.05 and 0.16 K3 for the sampling and noise errors, respectively. The fourth-order moment (FOM) and kurtosis values throughout the CBL were not significantly different to those of a Gaussian distribution. Both showed also maxima in the IL but these were not statistically significant taking the measurement uncertainties into account. We conclude that these measurements permit the validation of large eddy simulation results and the direct investigation of turbulence parameterizations with respect to temperature.

A nonperturbative quantum electrodynamic approach to the theory of laser induced high harmonic generation

Using nonperturbative quantum electrodynamics, we develop a scattering theory for high harmonic generation (HHG). A transition rate formula for HHG is obtained. Applying this formula, we calculate the spectra of high harmonics generated from different noble gases shined by strong laser light. We study the cutoff property of the spectra. The data show that the cutoff orders of high harmonics are greater than that predicted by the “3.17” cutoff law. As a numerical experiment, the data obtained from our repeated calculations support the newly derived theoretical expression of the cutoff law. The cutoff energy of high harmonics described by the new cutoff law, in terms of the ponderomotive energy Up and the ionization potential energy Ip, is 3.34Up + 1.83Ip. The higher cutoff orders predicted by this theory are due to the absorption of the extra photons, which participate only the photon-mode up-conversion and do nothing in the photoionization process.

Fluorescence correlation spectroscopy of gold nanoparticles, and its application to an aptamer-based homogeneous thrombin assay

We have studied the fluorescence properties and diffusion behaviors of gold nanoparticles (GNPs) in solution by using fluorescence correlation spectroscopy (FCS) at single molecule level. The GNPs display a high photo-saturation feature. Under illumination with strong laser light, they display higher brightness per particle (BPP) despite their low quantum yields. Based on the unique fluorescence properties and diffusion behaviors of GNPs, we have developed a sensitive and homogenous thrombin assay. It is based on a sandwich strategy and is making use of GNPs to which two different aptamers are conjugated. When the differently aptamer-labeled GNPs are mixed with solutions containing thrombin, the affinity reaction causes the GNPs to form dimers or oligomers. This leads to an increase in the diffusion time of the GNPs in the detection volume that is seen in FCS. The FCS method enables sensitive detection of the change in the characteristic diffusion time of the GNPs before and after the affinity reaction. Quantitative analysis of thrombin is based on the measurement of the change in the diffusion time. Under optimal conditions, the calibration plot is linear in the 0.5 nM to 110 nM thrombin concentration range, and the detection limit is 0.5 nM. The method was successfully applied to the direct determination of thrombin in human plasma.

Broadband Plasmonic Absorber for Photonic Integrated Circuits

Surface plasmon polaritons losses have long been considered as a fatal shortcoming of plasmonics based information transport. Here, we propose a plasmonic absorber utilizing this shortcoming to absorb the stray light in photonic integrated circuits (PICs). Benefiting from adiabatic mode evolution, its performance is insensitive to incident wavelength with bandwidth larger than 300 nm, and is robust against surrounding environment and temperature. Besides, the use of metal enables it to be very compact and beneficial to thermal dissipation. With this 40-\(\mu \) m-long absorber, the absorption efficiency can be over 99.8% at 1550 nm, with both the reflectivity and transmittance reduced to <;0.1%. Such a device may find various applications in PICs, to eliminate the residual strong pump laser or stray light.

Influence of the Sampling Rate and Noise Characteristics on Prediction of the Maximal Safe Laser Exposure in Human Skin Using Pulsed Photothermal Radiometry

Pulsed photothermal radiometry (PPTR) allows for noninvasive determination of the laser-induced temperature depth profile in strongly scattering samples, including human skin. In a recent experimental study, we have demonstrated that such information can be used to derive rather accurate predictions of the maximal safe radiant exposure on an individual patient basis. This has important implications for efficacy and safety of several laser applications in dermatology and aesthetic surgery, which are often compromised by risk of adverse side effects (e.g., scarring, and dyspigmentation) resulting from nonselective absorption of strong laser light in epidermal melanin. In this study, the differences between the individual maximal safe radiant exposure \((H_{\mathrm{max}})\) values as predicted from PPTR temperature depth profiling performed using a commercial mid-IR thermal camera (as used to acquire the original patient data) and our customized PPTR setup are analyzed. To this end, the latter has been used to acquire 17 PPTR records from three healthy volunteers, using 1 ms laser irradiation at 532 nm and a signal sampling rate of 20 000 \(\mathrm{s}^{-1}\). The laser-induced temperature profiles are reconstructed first from the intact PPTR signals, and then by binning the data to imitate the lower sampling rate of the IR camera (1000 fps). Using either the initial temperature profile in a dedicated numerical model of heat transfer or protein denaturation dynamics, the predicted levels of epidermal thermal damage \((\varOmega )\) and the corresponding \(H_{\mathrm{max}}\) are compared. A similar analysis is performed also with regard to the differences between noise characteristics of the two PPTR setups.

A portable double-slit quantum eraser with individual photons

The double-slit experiment has played an important role in physics, from supporting the wave theory of light, via the discussions of the wave–particle duality of light (and matter) to the foundations of modern quantum optics. Today it keeps playing an active role in the context of quantum optics experiments involving single photons. In this paper, we present a truly portable double-slit apparatus which demonstrates both the wave–particle duality of light and the phenomenon of quantum erasing. The device can be operated either with strong laser light and screen projection, or with individual photons, in which case quantum interference and quantum erasing are detected by a photomultiplier whose pulses are rendered acoustically by means of a loudspeaker. Alternatively, the phenomena can be displayed using multimedia projection of oscilloscope traces.

Measurements of electron density and temperature in a miniature microwave discharge ion thruster using laser Thomson scattering technique

In order to improve the thrust performance of a miniature microwave discharge ion thruster, the relationship between electron number density/temperature and operational conditions, mass flow rate, incident microwave power and magnetic field strength were measured by means of laser Thomson scattering. A photon counting method and a triple grating spectrometer were used against a small Thomson scattering signal and a strong stray laser light. Electron number density increased with incident microwave power and was saturated at critical incident microwave power; it was about 1.2 × 1018 m−3 at incident microwave power >8 W. In addition, electron number density increased with mass flow rate and became saturated; it was about 1.7 × 1018 m−3 at mass flow rate > 0.04 mg s−1. The electron number density gradually increased with an increase in the number of magnets, i.e. magnetic field strength. There was a sudden jump at thirteen magnets, although the thruster failed to ignite at fourteen magnets. This is because there is an optimum distance between the antenna and the electron cyclotron resonance layer. These results suggest that future improvement in thrust efficiency in miniature microwave discharge ion thrusters may come from the fine adjustment of the magnetic field configuration inside the discharge chamber.

Electrically Tunable and Dual-Wavelength Semiconductor Laser with a Liquid Crystal Display

An electrically tunable semiconductor laser with a liquid crystal display (LCD) and a commercially available laser diode is presented. We tested two types of LCD under strong laser light and, on the basis of the results, selected the supertwist-nematic (STN) LCD with a passive matrix. Tuning is achieved up to 5 nm by moving a single stripe pattern displayed on the LCD. The wavelength shifts in 0.553 nm/cell, which agrees well with the calculated resolution derived from the diffraction grating formula. Dual-wavelength oscillation is also achieved up to a wavelength separation of 4.62 nm using the double stripe pattern.

Structure and Dynamics of Isotropic Order

“Isotropic order”. Soft condensed matter system can form the huge length scale order. SmBPIso is characterized by the simultaneous presence of the local order parameter of an helix and of a smectic layer, while being spontaneously isotropic without any characteristic discontinuity on a mesoscopic length scale. It is great advantage for the optical devices that the spectrum of the iridescent color of SmBPIso is completely equivalent by the changing the viewing angle because of the special isotropic symmetry and its wavelength can be successively controlled by changing temperature. Recently, we found the color can be tuned by shining the strong pulsed laser light. Then we can artificially design the special pattern of the “structural color” by scanning and on/off the laser light beam. Response time of the color shift is not so fast but not so slow (~200msec) in spite of the existence of the complicated inter-connected multi-lamellar structure. We also confirms experimentally that the existence of the collective fluctuation mode just around the sub second by the dynamic light scattering measurement. Relaxation time can be assigned as reorientation motion of the helical pitch, which must be correlated to the dynamics of the shrinkage/elongation of the inter-connected multi-lamellar structure through the coupling between two types of the liquid crystalline orders. Furthermore, we found that cubic SmBP reenter the SmBPIso at super cooling temperature (Tsc) in the twin poor region. Since Smectic A phase appear by applying the heating shock and is stable until Tsc where cubic SmBP reappear. So we can conclude that the re-entrant SmBPIso is super-cooled state. We also found the power law slow dynamics in the director orientation fluctuation as similar to the conven smectic-A phase, which is hidden by the super cooling of SmBP tional liquid-glass transition. However, it should be noted that

Anisotropic bulletlike emission of terminal ethynyl fragment ions: Ionization of ethynylbenzene-d under intense femtosecond laser fields

The authors investigated Coulomb explosions of ethynylbenzenes under intense femtosecond laser fields. Deuteration on the edge of the triple bond gave information about specific fragment emissions and the contribution of hydrogen migration. Some fragments not resulting from migration were emitted in the direction of laser polarization. These were ethynyl fragment ions (D(+), CD(+), C(2)D(+), and C(3)D(+)). Although two bonds have to be cleaved to produce C(3)D(+), the rigid character of the triple bond was maintained in the Coulomb explosion process. In contrast, fragment ions, which are formed after single or double hydrogen migration, showed isotropic emissions with distinct kinetic energies. The character of the substituents has been found to hold even under strong laser light fields where violent fragmentation took place. The ethynyl parts were emitted like bullets from the molecular frame of ethynylbenzene despite the explosion into pieces of the main body of benzene ring.