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In today’s heavily competitive game market making a game that stands out from the huge amount of available games has become very important. Even though the game might not be the most unique one out there, it still can offer a better playing experience than a similar competitor’s product by having better usability. Usability research could provide game companies with the tools needed to improve their games usability. The aim of this survey was to find out if game companies are doing usability research and investigate their views on game usability. This research was conducted by sending a survey to Northern European game companies’ and the results were analyzed using descriptive statistics and content analysis. Game companies regarded game usability to be very important in games and saw it as a broad concept. Their view corresponded well with the literature view that emphasises user experience. Companies used multitude of usability methods to improve their games usability but these methods and their usage has not stabilized. The most used methods were playtesting and observation whereas heuristic evaluation was one of the least used methods which seemed to be unknown method among the respondents.
Vuonna 1984 Michael Berry havaitsi kvanttimekaanisten geometristen vaiheiden merkityksen kvanttimekaniikassa. Siksi niitä kutsutaan yleisesti Berryn vaiheiksi. Geometrinen vaihe syntyy, kun systeemin Hamiltonin operaattorin parametrit kehittyvät adiabaattisesti parametriavaruudessa. Vaihetta sanotaan geometriseksi, koska se riippuu parametriavaruuden geometriasta. Tämän tutkielman tavoitteena on selvittää, mikä Berryn vaihe on, mistä se saa syntynsä, ja miten se ilmenee tietyissä suhteellisen yksinkertaisissa kvanttisysteemeissä. Sitä ennen tehdään kuitenkin selväksi, mitä geometrisella vaiheella tarkoitetaan. Se ei suinkaan ole pelkästään kvanttimekaaninen ilmiö, vaan se ilmenee myös klassisessa fysiikassa. Lisäksi esitellään geometristen vaiheiden synnyn kannalta keskeiset adiabaattisuuden ja epäholonomian käsitteet. Tarkoituksena on ollut koota tietoa eri lähteistä omaksi kokonaisuudekseen, josta lukija saa käsityksen Berryn vaiheesta ja siihen liittyvistä keskeisistä käsitteistä.
Abstract The main aim of this work was to design CMOS receiver channels for the integrated receiver chip of a pulsed time-of-flight (TOF) laser rangefinder. The chip includes both the receiver channel and the time-to-digital converter (TDC) in a single die, thus increasing the level of integration of the system, with the corresponding advantages of a cheaper price and lower power consumption, for example. Receiver channels with both linear and leading edge timing discriminator schemes were investigated. In general the receiver channel consists of a preamplifier, a postamplifier and a timing comparator. Since a large systematic timing error may occur due to high variation in the amplitude of the received echo, a leading edge timing discriminator scheme with time domain walk error compensation is proposed here, making use of the TDC already available in the chip to measure the slew rate of the pulse and using that information to evaluate the timing error. This compensation scheme benefits from the fact that compensation can be continued even though the signal is clipped in the amplitude domain, because the slew rate continues to increase even then. The receiver channel with leading edge detection and time domain walk error compensation achieved a compensated timing walk error of ±4.5 mm within a dynamic range of more than 1:10000. The standard deviation in single shot precision was less than 25 mm with an SNR of more than 20. The usability of the receiver channel in pulsed TOF laser rangefinders was verified by making actual time-of-flight measurements on a calibrated measurement track. The linearity of the receiver chip was better than ±5 mm in a measurement range from 3 m to 21 m, with the dynamic range of the receiver channel reaching more than 1:2000. An integrated CMOS laser diode pulser was also demonstrated to prove its functionality for generating ampere-scale peak current pulses through a low ohmic load and a laser diode. The CMOS pulser achieved a peak current pulse with the amplitude of ~1 A, an optical pulse width of ~2.5 ns and a rise time of ~1 ns with a 5 V power supply.
For two-dimensional topological insulators, the integer and intrinsic (without external magnetic field) quantum Hall effect is described by the gauge anomalous (2+1)-dimensional [(2+1)-d] Chern-Simons (CS) response for the background gauge potential of the electromagnetic U(1) field. The Hall conductance is given by the quantized prefactor of the CS term, which is a momentum-space topological invariant. Here, we show that three-dimensional crystalline topological insulators with no other symmetries are described by a topological (3+1)-dimensional [(3+1)-d] mixed CS term. In addition to the electromagnetic U(1) gauge field, this term contains elasticity tetrad fields E-mu(a) (r, t) = partial derivative X-mu(a) (r, t) which are gradients of crystalline U(1) phase fields X-a (r, t) and describe the deformations of the crystal. For a crystal in three spatial dimensions a = 1, 2, 3 and the mixed axial-gravitational response contains three parameters protected by crystalline symmetries: the weak momentum-space topological invariants. The response of the Hall conductance to the deformations of the crystal is quantized in terms of these invariants. In the presence of dislocations, the anomalous (3+1)-d CS term describes the Callan-Harvey anomaly inflow mechanism. The response can be extended to all odd spatial dimensions. The elasticity tetrads, being the gradients of the lattice U(1) fields, have canonical dimension of inverse length. Similarly, if such tetrad fields enter general relativity, the metric becomes dimensionful, but the physical parameters, such as Newton's constant, the cosmological constant, and masses of particles, become dimensionless.
We discuss the possibility of gravitational Nieh-Yan anomaly of the type ∂μj~5μ=γT2Ta∧Ta in topological Weyl materials, where T is temperature and Ta is the effective or emergent torsion. As distinct from the non-universal parameter ⋀ in the conventional (zero temperature) Nieh-Yan anomaly — with canonical dimensions of momentum — the parameter γ is dimensionless. This suggests that the dimensionless parameter is fundamental, being determined by the geometry, topology and number of the number of chiral quantum fields without any explicit non-universal UV scales. This conforms with previous results in the literature, as well as spectral flow calculations using torsional magnetic field at finite temperature.
We discuss the possibility of torsional Nieh-Yan anomaly of the type partial derivative(mu) (ej(5)(mu)) = gamma T-2 (T-a Lambda T-a) in Weyl superfluids, where T is the infrared (IR) temperature scale and T a is the effective or emergent torsion from the superfluid order parameter. As distinct from the dimensionful ultraviolet (UV) parameter Lambda(2) in the conventional torsional Nieh-Yan anomaly, the parameter gamma is dimensionless in canonical units. This suggests that such dimensionless parameter may be fundamental, being determined by the geometry, topology, and number of chiral quantum fields in the system. By comparing this to a Weyl superfluid with low-temperature corrections, T
Relativistic gravitational anomalies lead to anomalous transport coefficients that can be activated at finite temperature in hydrodynamic and condensed matter systems with gapless, linearly dispersing fermions. One is the chiral vortical effect (CVE), an anomalous chiral current along the system's rotation axis, expressed in terms of a gravimagnetic metric field in a rotating frame with mixed gravitational anomaly. Another one arises in the presence of hydrodynamically independent frame fields (and spin connection) and leads to the thermal chiral torsional effect (CTE). We discuss the relation of CVE, CTE, and gravitational anomalies for relativistic fermions from the perspective of nonzero torsion and the Nieh-Yan anomaly when the currents depend on the frame fields and connection instead of the metric. The transport coefficients induced by the two gravitational anomalies at zero frequency and momentum are found to be closely related and equal. At level of linear response, their difference is demarcated whether or not torsion is nonzero and the existence of nonmetric degrees of freedom in the hydrodynamic constitutive relations with sources. In particular, the relativistic anomaly from torsion is well defined, since instead of an UV divergent term the chemical potential or temperature scales enter. This is closely related to the derivation of CVE from the fourth order in gradients gravitational anomaly and its appearance already in the linear response. However, the torsional anomaly is second order in gradients and directly contributes in linear response for CTE, implying also the same for CVE. For an example where the two anomalies are sourced independently, we consider chiral p+ip Weyl superfluids and superconductors rotating at finite temperature. At low energies in the linear approximation, the system is effectively relativistic along a special anisotropy axis. The hydrodynamics is governed by two velocities, the normal velocity vn and superfluid velocity vs. The existence of the two thermal anomalies in the condensate follows from the normal component rotation and the dependence of the momentum density on the superfluid velocity (order parameter). In the CVE, the chiral current is produced by the solid body rotation of the normal component with (angular) velocity vn=ω×r. In the CTE, a chiral current is produced by the vorticity of the superfluid velocity ∇×vs, which in the low-energy quasirelativistic effective theory plays the role of gravitational torsion. In thermal equilibrium, ⟪∇×vs⟫=2ω spatially averaged and the two gravitational anomaly currents cancel each other. This is a version of the Bloch theorem for axial currents, prohibiting finite current in equilibrium, realized as the cancellation of two gravitational anomalies with independent sources: gravimagnetic rotation field ω and torsion from vs. Although the latter physically represents the superfluid vorticity similar to the CVE, in the low-energy quasirelativistic theory, it arises from torsion coupling to the normal component chiral fermions.
Topologically protected superfluid phases of He3 allow one to simulate many important aspects of relativistic quantum field theories and quantum gravity in condensed matter. Here we discuss a topological Lifshitz transition of the effective quantum vacuum in which the determinant of the tetrad field changes sign through a crossing to a vacuum state with a degenerate fermionic metric. Such a transition is realized in polar distorted superfluid He3-A in terms of the effective tetrad fields emerging in the vicinity of the superfluid gap nodes: The tetrads of the Weyl points in the chiral A-phase of He3 and the degenerate tetrad in the vicinity of a Dirac nodal line in the polar phase of He3. The continuous phase transition from the A-phase to the polar phase, i.e., the transition from the Weyl nodes to the Dirac nodal line and back, allows one to follow the behavior of the fermionic and bosonic effective actions when the sign of the tetrad determinant changes, and the effective chiral spacetime transforms to antichiral "anti-spacetime." This condensed matter realization demonstrates that while the original fermionic action is analytic across the transition, the effective action for the orbital degrees of freedom (pseudo-EM) fields and gravity have nonanalytic behavior. In particular, the action for the pseudo-EM field in the vacuum with Weyl fermions (A-phase) contains the modulus of the tetrad determinant. In the vacuum with the degenerate metric (polar phase) the nodal line is effectively a family of 2+1d Dirac fermion patches, which leads to a non-analytic (B2-E2)3/4 QED action in the vicinity of the Dirac line.
Theory of elasticity in topological insulators has many common features with relativistic quantum fields interacting with gravitational fields in the tetrad form. Here we discuss several issues in the effective topological (pseudo)electromagnetic response in three-dimensional weak crystalline topological insulators with no time-reversal symmetry that feature elasticity tetrads, including a mixed “axial-gravitational” anomaly. This response has some resemblance to “quasitopological” terms proposed for massless Weyl quasiparticles with separate, emergent fermion tetrads. As an example, we discuss the chiral/axial anomaly in superfluid 3He-A. We demonstrate the principal difference between the elasticity tetrads and the Weyl fermion tetrads in the construction of the topological terms in the action. In particular, the topological action expressed in terms of the elasticity tetrads cannot be expressed in terms of the Weyl fermion tetrads since in this case the gauge invariance is lost.
3+1-dimensional Weyl fermions in interacting systems are described by effective quasi-relativistic Green’s functions parametrized by a 16 element matrix eα μin an expansion around the Weyl point. The matrix eα μcan be naturally identified as an effective tetrad field for the fermions. The correspondence between the tetrad field and an effective quasi-relativistic metric gμν governing the Weyl fermions allows for the possibility to simulate different classes of metric fields emerging in general relativity in interacting Weyl semimetals. According to this correspondence, there can be four types of Weyl fermions, depending on the signs of the components g00 and g00 of the effective metric. In addition to the conventional type-I fermions with a tilted Weyl cone and type-II fermions with an overtilted Weyl cone for g00 > 0 and respectively g00 > 0 or g00 < 0, we find additional “type-III” and “type-IV” Weyl fermions with instabilities (complex frequencies) for g00 < 0 and g00 > 0 or g00 < 0, respectively. While the type-I and type-II Weyl points allow us to simulate the black hole event horizon at an interface where g00 changes sign, the type-III Weyl point leads to effective spacetimes with closed timelike curves.
Abstract The effects of the inhomogeneity of a time resolving CMOS single-photon avalanche diode array on the fluorescence-suppressed, time-gated, Raman spectroscopy device was experimentally studied here. Raman spectroscopy device using a 532 nm pulsed laser and a single time resolving single-photon avalanche diode (SPAD) with a micro step motor was developed to study these effects. A single SPAD with a step motor allows us to test the performance which could be achieved with an ideal line detector without any nonlinearities and inhomogeneities because the same SPAD and time interval measurement unit is used in every spectral point. Additionally, the single element can be replaced by a SPAD array with an on-chip time-to-digital converter (TDC) to make comparison measurements to clarify the effects of inhomogeneity. These comparison measurements were made by using an array of 256 elements with an on-chip 100 ps TDC and showed that the deterioration of Raman spectra is larger when fluorescence lifetimes and levels are shorter and higher, respectively.
Abstract Raman spectroscopy has proved to have potential in deep surface analytical applications. We present here, to the best of our knowledge, the first time depth analysis of semi-transparent media by a depth-resolving Raman spectrometer based on an adjustable time-correlated CMOS SPAD (single-photon avalanche diode) line sensor that can measure the depth of target samples embedded in a centimeter-scale semi-transparent medium simultaneously with a normal Raman depth profiling operation and suppress the fluorescence background by means of adjustable picosecond time gating. The variability of the depth derivation was measured to be ± 0.43 cm at depths ranging from 2 to 9 cm. In addition, the advantages of the adjustable picosecond time gating in terms of depth derivation and fluorescence background suppression performance were shown by comparing gate widths ranging from 100 ps to 13 ns. We believe that the technology concerned could pave the way for a new kind of compact, practical depth-resolving Raman spectrometer for deep subsurface analytical applications.
Abstract The effect of the timing of the biasing of a single photon avalanche diode (SPAD) on the accuracy of a time-gated SPAD array has been studied in this work. The measurement was realized in a time-gated Raman spectrometer utilizing a 16×256 CMOS SPAD array with on-chip time gating electronics. SPADs have to be biased into the Geiger-mode just before arriving Raman scattered photons from the sample to achieve synchronous measurements with a pulsed laser, and to minimize the dark count noise. The practical realization is, however, not straight-forward due to the strict timing requirements (∼50ps). With the shown biasing arrangement high timing accuracy and low noise can be achieved without sacrificing the fill factor of the detector array.
Abstract A pulse width-controlled CMOS pulser for a semiconductor laser diode (LD) and a time-gated time-resolved 8×4 single-photon avalanche diode array with a time-to-digital converter (TDC) were designed on a single integrated circuit and simulated by using a 150 nm technology. The pulse width of the driving current can be adjusted from 0.5 ns to 2.5 ns with a resolution of 100 ps. The start time of the time-gating can be adjusted over a dynamic range of 4.8 ns with a resolution of 100 ps and, furthermore, a 121 ps time-gating can be achieved. The returning photons are detected by the TDC with a resolution of 50 ps and stored to the 128 14-bit counters for merging to the distribution time-of-flight histogram. The average power consumption of the whole system was 377 mW at a repetition rate of 10 MHz.
Abstract A characterization environment was built to verify the timing characteristics of a single photon avalanche diode (SPAD) array designed for time-gated Raman spectroscopy. The characterization was applied to a 256 × 16 SPAD array that employed an on-chip time-to-digital converter (TDC) with a 50–100-ps resolution for time resolving. The timing skew and the time window homogeneity across the array were resolved, moving the time-resolving windows over an optical pulse by picosecond-level delay steps. A typical one 160-ps skew across the array was measured. The TDC time bins had average sizes of 33–144 ps while their deviation across the array was 8–12 ps. The method is applicable to multidetector time-correlated single photon counting systems that can finely adjust the delay between the optical pulse and the reference signal.
Abstract Remote Raman spectroscopy is widely used to detect minerals, explosives and air pollution, for example. One of its main problems, however, is background radiation that is caused by ambient light and sample fluorescence. We present here, to the best of our knowledge, the first time a distance-resolving Raman radar device that is based on an adjustable, time-correlated complementary metal-oxide-semiconductor (CMOS) single-photon avalanche diode line sensor which can measure the location of the target sample simultaneously with the normal stand-off spectrometer operation and suppress the background radiation dramatically by means of sub-nanosecond time gating. A distance resolution of 3.75 cm could be verified simultaneously during normal spectrometer operation and Raman spectra of titanium dioxide were distinguished by this system at distances of 250 cm and 100 cm with illumination intensities of the background of 250 lux and 7600 lux, respectively. In addition, the major Raman peaks of olive oil, which has a fluorescence-to-Raman signal ratio of 33 and a fluorescence lifetime of 2.5 ns, were distinguished at a distance of 30 cm with a 250 lux background illumination intensity. We believe that this kind of time-correlated CMOS single-photon avalanche diode sensor could pave the way for new compact distance-resolving Raman radars for application where distance information within a range of several metres is needed at the same time as a Raman spectrum.
Abstract The effects of the position and width of the time gate on the available signal-to-noise ratio in a time-gated Raman spectrometer are analyzed and measured. The Raman spectrometer used is based on a high power, 532 nm, pulsed laser (500 ps FWHM) and a time-resolving circuit with a single photon avalanche diode (SPAD) detector which is moved by a microstep motor to derive the whole Raman spectrum. The times of arrival of the scattered photons are recorded and the effectiveness of different time gate positions and widths are analyzed by post-processing the measured and simulated data. It is shown from measurements performed on olive and sesame seed oil samples having fluorescence lifetimes of 2.5 ns and 2 ns and Raman-to-fluorescence photon ratios of 0.03 and 0.003, respectively, that the fluorescence background can be substantially suppressed if the width and position of the time gate are properly selected.
Abstract This integrated receiver channel designed for a pulsed time-of-flight (TOF) laser rangefinder consists of a fully differential transimpedance amplifier channel and a timing discriminator. The amplitude-dependent timing walk error is compensated by measuring the width and rise time of the received pulse echo and using this information for calibration. The measured bandwidth, transimpedance and minimum detectable signal (SNR ~10) of the receiver channel are 230 MHz, 100 kΩ and ~1 μA respectively. The single-shot precision of the receiver is ~3 cm at an SNR of 13 and the measurement accuracy is ±4 mm with compensation within a dynamic range of~1:100,000. The receiver circuit was realized in a $0.35 μm CMOS process and has a power consumption of 150 mW. The functionality of the receiver channel was verified over a temperature range of -20 °C to +50 °C.
Abstract The fluorescence background in Raman spectroscopy can be effectively suppressed by using pulsed lasers and time-gated detectors. A recent solution to reduce the high complexity and bulkiness of the time-gated systems is to implement the detector by utilizing time-resolved single-photon avalanche diodes (SPADs) fabricated in complementary-metal-oxide-semiconductor (CMOS) technology. In this study, we investigate the effects of fluorescence-to-Raman ratio, recording time and excitation intensity on the quality of Raman spectra measured by using one of the furthest developed fluorescence-suppressed Raman spectrometers based on a time-resolved CMOS SPAD line sensor. The objectives were to provide information on the significance of the different causes behind the distortion of the measured Raman spectra with various measurement conditions and to provide general information on the possibilities to exploit the high-intensity non-stationary pulsed laser excitation to gain additional improvement on the spectral quality due to laser-induced fluorescence saturation. It was shown that the distortion of the spectra with samples having short fluorescence lifetimes (~2 ns) and high fluorescence-to-Raman ratios, i.e. with challenging samples, is dominated by the timing skew of the sensor instead of the shot noise caused by the detected events. In addition, the actual reason for the observed improvement in the spectral quality as a function of excitation intensity was discovered not to be the conventionally thought increased number of detected photons but rather the laser-induced fluorescence saturation. At best, 26% improvement to the signal-to-noise ratio was observed due to fluorescence saturation.
All realistic second order phase transitions are undergone at finite transition rate and are therefore non-adiabatic. In symmetry-breaking phase transitions the non-adiabatic processes, as predicted by Kibble and Zurek [1, 2], lead to the formation of topological defects (the so-called Kibble-Zurek mechanism). The exact nature of the resultingdefects depends on the detailed symmetry-breaking pattern.
We describe a crystalline topological insulator (TI) phase of matter that exhibits spontaneous polarization in arbitrary dimensions. The bulk polarization response is constructed by coupling the system to geometric deformations of the underlying crystalline order, represented by local lattice vectors - the elasticity tetrads. This polarization results from the presence of (approximately) flat bands on the surface of such TIs. These flat bands are a consequence of the bulk-boundary correspondence of polarized topological media, and contrary to related nodal line semimetal phases also containing surface flat bands, they span the entire surface Brillouin zone. We also present an example Hamiltonian exhibiting a Lifshitz transition from the nodal line phase to the TI phase with polarization. In addition, we discuss a general classification of three-dimensional (3D) crystalline TI phases and invariants in terms of the elasticity tetrads. The phase with polarization naturally arises from this classification as a dual to the previously better-known 3D TI phase exhibiting quantum (spin) Hall effect. Besides polarization, another implication of the large surface flat band is the susceptibility to interaction effects such as superconductivity: The mean-field critical temperature is proportional to the size of the flat bands, and this type of system may hence exhibit superconductivity with a very high critical temperature.
We describe a crystalline topological insulator (TI) phase of matter that exhibits spontaneous polarization in arbitrary dimensions. The bulk polarization response is constructed by coupling the system to geometric deformations of the underlying crystalline order, represented by local lattice vectors—the elasticity tetrads. This polarization results from the presence of (approximately) flat bands on the surface of such TIs. These flat bands are a consequence of the bulk-boundary correspondence of polarized topological media, and contrary to related nodal line semimetal phases also containing surface flat bands, they span the entire surface Brillouin zone. We also present an example Hamiltonian exhibiting a Lifshitz transition from the nodal line phase to the TI phase with polarization. In addition, we discuss a general classification of three-dimensional (3D) crystalline TI phases and invariants in terms of the elasticity tetrads. The phase with polarization naturally arises from this classification as a dual to the previously better-known 3D TI phase exhibiting quantum (spin) Hall effect. Besides polarization, another implication of the large surface flat band is the susceptibility to interaction effects such as superconductivity: The mean-field critical temperature is proportional to the size of the flat bands, and this type of system may hence exhibit superconductivity with a very high critical temperature.
Abstract Single-Photon Avalanche Photodiodes (SPADs) were fabricated and characterized in 150 nm CMOS technology. The SPAD is based on a p+/nwell junction with a p-substrate guard ring. In addition, a compact gain switched quantum well (QW) laser diode with a CMOS driver was used with the proposed SPAD for time-resolved diffuse optics measurements. The measured impulse response function (IRF) of the SPADs was ∼50 ps at best. Two phantoms were measured to demonstrate the suitability of SPADs for time-resolved diffuse optics imaging (TRDOI).
Abstract A laser rangefinder device based on pulsed time-of-flight (TOF) distance measurement techniques was constructed and tested. Key blocks of the system are the integrated receiver channel and the integrated time-to-digital converter (TDC) fabricated in a 0.35-um CMOS technology. The receiver-TDC chip set is capable of measuring the time position, rise time and pulse width of incoming optical pulses with ps precision in the amplitude range of more than 1: 50 000. The timing detection is based on leading edge detection in the receiver channel, and the amplitude-dependent timing error is compensated for by utilizing the multichannel TDC. A measurement distance of 100 m is achieved to a target with a reflectance of about 10% at the signal level of SNR = 6, with an optical output power and receiver aperture of 12 W and 18 mm, respectively.
Abstract The timing accuracy of a single-photon avalanche diode (SPAD) based receiver is analyzed as a function of excess bias voltage. The width of the used optical pulse was 100 ps, which matches well with the jitter of the used SPAD receiver fabricated in a 0.35 pm HVCMOS technology. The timing error was measured to be 900 ps within the excess bias voltage range of ~1.25 V-3.25 V. The single-shot resolution changes from 420 ps to 160 ps (FWHM), respectively.
Abstract A 16 × 256 element single-photon avalanche diode array with a 256-channel, 3-bit on-chip time-to-digital converter (TDC) has been developed for fluorescence-suppressed Raman spectroscopy. The circuit is fabricated in 0.35 μm high-voltage CMOS technology and it allows a measurement rate of 400 kframe/s. In order to be able to separate the Raman and fluorescence photons even in the presence of the unavoidable timing skew of the timing signals of the TDC, the time-of-arrival of every detected photon is recorded with high time resolution at each spectral point with respect to the emitted short and intensive laser pulse (~150 ps). The dynamic range of the TDC is set so that no Raman photon is lost due to the timing skew, and thus the complete time history of the detected photons is available at each spectral point. The resolution of the TDC was designed to be adjustable from 50 ps to 100 ps. The error caused by the timing skew and the residual variation in the resolution of the TDC along the spectral points is mitigated utilizing a calibration measurement from reference sample with known smooth fluorescence spectrum. As a proof of concept, the Raman spectrum of sesame seed oil, having a high fluorescence-to-Raman ratio and a short fluorescence lifetime of 1.9 ns, was successfully recorded.
Abstract Raman analysis of rock samples containing rare earth elements (REEs) is challenging due to the strong fluorescence, which may mask the weaker Raman signal. In this research, time‐gated (TG) Raman has been applied to the construction of the mineral distribution map from REE‐bearing rock. With TG Raman, material is excited with a short subnanosecond laser pulse, and the Raman signal is collected within a picosecond‐scale time window prior to the formation of a strong fluorescent signal by means of single‐photon avalanche diode array. This allows signal readout with a significantly reduced fluorescence background. TG Raman maps are used to reveal the location of valuable minerals and are compared with the elemental distribution given by laser‐induced breakdown spectroscopy. The analysis was carried out from a REE‐bearing rock, nepheline syenite sample from the Norra Kärr deposit, where REEs are mainly hosted in eudialyte and catapleiite. The combination of these two complimentary laser spectroscopic methods offers valuable elemental and mineralogical information about rocks.
Abstract The focus of this study was to assess the feasibility of time-gated Raman spectroscopy for stainless steel pickle liquor acid quantification. Pickle liquor is used for dissolving metal surface impurities during the pickling process. The pickle liquor samples consisted mainly of 11–89 g/L HNO3, 20–160 g/L H2SO4, 5–57 g/L HF and stainless steel residue. Raman peaks correlating with the different acids were identified in both aqueous and pickle liquor solutions. The linearity between Raman scattering intensity and acid concentration was studied. Multivariate PLSR calibration for pickle liquor HNO3, H2SO4 and HF quantification was also investigated. Time-gated Raman spectroscopy was found to be a promising technique for pickle liquor HNO3 and H2SO4 quantification.
A time crystal is a macroscopic quantum system in periodic motion in its ground state. In our experiments, two coupled time crystals consisting of spin-wave quasiparticles (magnons) form a macroscopic two-level system. The two levels evolve in time as determined intrinsically by a nonlinear feedback, allowing us to construct spontaneous two-level dynamics. In the course of a level crossing, magnons move from the ground level to the excited level driven by the Landau-Zener effect, combined with Rabi population oscillations. We demonstrate that magnon time crystals allow access to every aspect and detail of quantum-coherent interactions in a single run of the experiment. Our work opens an outlook for the detection of surface-bound Majorana fermions in the underlying superfluid system, and invites technological exploitation of coherent magnon phenomena – potentially even at room temperature.