The circular dichroism spectral sensing effect of a chiral double-layer plasmon metasurface is investigated theoretically. By analyzing the spatial distribution of the electromagnetic field in the structure, it can be found that the enhanced chiral resonance response of the artificial structure is due to the local plasmon resonance in the slit and the coupling effect between two metasurfaces, and the circular dichroism transmission spectrum and co-polarized transmission spectrum of this structure respond differently to the refractive index changes of the biochemical layer. Under proper structural parameters, the sensitivity of circular co-polarized spectrum and circular dichroism spectrum can reach 109 nm/RIU and 111 nm/RIU, respectively. It is shown that the artificial chiral structure has the functions of co-polarized spectrum and circular dichroism spectrum sensing, and has potential application value in the field of new biochemical sensor devices.
As the main factors affecting the accuracy of spectral measurement, temperature and pressure are the research focus of developing high-precision spectral measuring instrument. A high-precision temperature and pressure control system for spectral measuring instrument is developed. The system is designed and optimized from the aspects of instrument structure, circuit design and control algorithm, so the long-term temperature control accuracy of the system can reach 0.003 °C, and long-term pressure control accuracy can reach 5.34 Pa. Under the condition of pressure control but without temperature control, the measurement results of methane gas concentration with a volume fraction of 300×10-6 fluctuates by 12.06×10-6 and the deviation σ is 3.26×10-6. While under the condition of both temperature and pressure control, the fluctuation of the corresponding measurement results is 4.03×10-6 and the deviation σ is 0.57×10-6. Results show that the high-precision temperature and pressure control system can improve the measurement accuracy and stability of the spectral measuring instrument, and also verify the reliability and feasibility of the system. It is shown that the developed temperature and pressure control system for spectral measuring instrument has reached the experimental and production standards, which provides reference for the development of similar high-precision spectral measuring instrument.
In order to realize the scanning requirements of the two-dimensional multi-axis differential absorption spectroscopy (MAX-DOAS) instrument, a control system for prism scanning is designed based on STM32 microprocessor and photoelectric encoder with the two-phase stepper motor driver chip TMC261 as the core. The requirements for rotational accuracy and resolution of two-dimensional MAX-DOAS external prism are analyzed, and then the system scheme is expounded from the two aspects of control system structure design and concrete implementation process. Measurement experiments are carried out to evaluate the actual effect of the designed system. Results show that the subdivision of the rotational stepping angle of the prism can be adjusted within the range from 0 to 256, the scanning resolution is up to 1.8°/256, the position accuracy error is less than 5%, and the absolute value of step angle accuracy error is less than 8%. It indicates that the designed scanning control system has a broad application prospect in optical instruments.
In order to realize the automatic acquisition of excimer laser induced breakdown spectrum (LIBS) and the convenient processing of spectral data, the whole system is programmed in modules by adopting LabVIEW actor framework, and a full-automatic real-time acquisition system of spectral data is successfully developed. The performance of the software has been tested on the experimental platform of excimer LIBS for elemental imaging of biological tissues. During the operation of the excimer LIBS experimental system at 3 Hz, the program didn’t appear the phenomenon such as jam, crash, data loss, and the correct element distribution map was obtained by processing the data automatically, which shows that the developed software meets the requirements of LIBS system in data acquisition, storage and processing speed.
The processing inspection of large-relative off-axis convex parabolic mirrors is one of the important challenges in optical processing inspection. Combined with a large relative aperture off-axis convex parabolic lens with a diameter of φ100 mm, an off-axis amount of 87.5 mm, and a radius of curvature of 500 mm, the grinding amount of the master mirror is calculated, and a detection method combining the process spherical compensation detection and off-axis Hindle ball detection is proposed. The new method effectively avoids the shortcomings of using either of the two traditional detection methods alone, not only saves processing costs, but also improves the detection accuracy. The precision root mean square (RMS) of the large-relative off-axis convex parabolic mirror processed at last is better than λ/40(λ=632.8 nm), which shows that this method is feasible and can be widely used in practical production and processing.
A structural design scheme is proposed for a 400 mm aperture capture and tracking telescope. In this scheme, the main mirror is supported by three-point flexible bottom support and ball head spindle side support to avoid the interference of support stress and ensure that the main mirror has high profile accuracy. And an indium steel connecting rod structure is used in the connection of primary mirror and secondary mirror to ensure that the distance between primary and secondary mirrors changes within the tolerance range under large temperature difference, so that the telescope has good image quality under the limit conditions. Furthermore, the finite element model of the whole structure of the telescope is established, and the shape accuracy of the main mirror and the structural strength of the barrel are analyzed. The root mean square (RMS) value of the main mirror shape is better than λ/40, and the relative eccentricity and inclination of primary mirror and secondary mirror are 3 μm and 2.5′′ respectively, which meets the index requirements. Finally, the optical parameters of the telescope are measured quantitatively by using laser interferometer and collimator, and it is found that the RMS value of optical system is better than λ/14, the full width at half maxima (FWHM) value of star point is 1.432, which is close to the diffraction limit level. The designed scheme has certain reference value for the structure design of similar telescopes.
Compared with traditional optical imaging techniques, ghost imaging has the advantages of high resolution and strong anti-noise capability. While compared with single-wavelength ghost imaging, multi-wavelength ghost imaging can not only reconstruct the spatial information of the target object to be measured, but also reconstruct its color information. Firstly, the theoretical basis of multi-wavelength ghost imaging is briefly introduced. Then the color reconstruction of the multi-wavelength ghost imaging is carried out by using Hadamard illumination pattern with the multi-wavelength ghost imaging with white illumination as the experimental architecture. The optimization experiment of expanding the spectral range is proposed, that is, increasing types of the wavelength, which improves the color brightness of the reconstructed image experimentally. It is believed that the research is helpful for the practical applications of multi-wavelength ghost imaging in the field of spectrum imaging.
In order to enable the fiber laser to efficiently pump and generate high power laser, the pump source is typically coupled into the active doped fiber through a duplet lens system. For there are some disadvantages of duplet lens system, it can be replaced by a compound parabolic concentrator to improve the pumping efficiency and simplify the coupling system. The compound parabolic concentrator can concentrate all the lights with incident angles less than its maximum acceptance angle to its exit surface, and most of the energy is concentrated within the active doped fiber’s acceptance angle, so it has high coupling efficiency. In addition, the compound parabolic concentrator has the advantages of simple structure, small size, and simple docking with the pump source. Simulation proves that the compound parabolic concentrator has higher coupling efficiency than the duplet lens system, which is very suitable for the pump source injection test of fiber laser and can provide conditions for generating high power laser.
In order to obtain high order harmonic spectra with high-intensity, a method of chirp-delay regulation is proposed to control the harmonic intensity of H+2 and D+2. The results show that, when driven by shorter pulse duration, both of the harmonic spectra of H+2 and D+2 mainly come from the falling-region of laser field. Therefore, by properly introducing a chirp in the falling-region of laser field, the high-intensity spectral continuum can be obtained, and the harmonic intensity of H+2 is higher than that of D+2. However, when driven by longer pulse duration, the main contribution of harmonic spectra of H+2 and D+2 come from the rising and the falling region of laser field, respectively. Thus, the corresponding high-intensity spectral continuum can be produced by introducing the chirps in the rising or the falling region of laser field, and the harmonic intensity of H+2 is lower than that of D+2 in this case. Finally, by selecting the appropriate spectral continuum and superposing the harmonics, a single attosecond pulse with the pulse duration of 36 as can be obtained.
In view of the fact that current avalanche photodiode (APD) test platforms have the disadvantages of redundant equipment and low test efficiency, an APD performance test system with field programmable gate array (FPGA) as the control core and TDC-GPX as the high-precision time-to-digital conversion chip is designed, which can realize the automatic test of APD performance parameters. In this work, a design method of stable single photon pulse signal output is designed, and the design scheme of photon counting, data processing and post-pulse parameter calculation using time-to-digital conversion is introduced. The experimental results show that the integrated light source of the test system has a full width at half maximum (FWHM) of 46.6 ps, a peak amplitude of 304.4 mV, and an amplitude jitter of 3.7%, which meets the requirements of the APD test for the input single photon source. It indicates that the test system can effectively test the APD performance parameters, and the test efficiency has been greatly improved.
As the optical nonreciprocity has very important applications in optical signal processing and quantum networks, the optical nonreciprocity in a two-cavity optomechanical system with two mechanical resonators is investigated. In the system, there is a Coulomb interaction between the two mechanical resonators and the two cavities are coupled together by optical fiber. Based on the time evolution equation of the system operator and the standard input-output relationship in frequency domain, the transmission amplitude equation is obtained. The results show that when the system are on the red-sideband, the quantum coherence between the two paths of the optomechanical interaction and the linearly-coupled interaction can make the system present the optical nonreciprocity. Furthermore, it is shown that the phase difference can not only determine whether optical nonreciprocity can occur in the system, but also determine the direction of optical nonreciprocity. It is also found that the optical nonreciprocity can be enhanced by increasing the strength of the effective optomechanical interactionor or the linearly-coupled strength between the two cavities.
Real state cloning is an important part of quantum cloning. However, for obtaining the optimal asymmetric real state cloning by using the method of optimizing the fidelity directly, the mathematical operation process is very cumbersome, and the results are not so simple and clear. For this reason, the method of coordinate system rotation transformation is introduced. Based on rotation transformation of the coordinate system, a real state cloning in the original coordinate system will become a well-known phase-covariant cloning in the new coordinate system. According to representation transformation, the optimization of asymmetric real state cloning can be realized easily in the original coordinate system by comparison with optimized asymmetric phase covariant cloning, that is, a set of coefficients for the optimized asymmetric real state clone transformation can be obtained. It is shown that using the method to optimize asymmetric real state cloning, the idea of processing operation is clear, and the optimization result is symmetrical, neat, and concise. In addition, the specific relationships between different coefficients of the optimized asymmetric real state clone can be obtained explicitly.
The atomic population and quantum entanglement in the system of binomial light field interacting with V-type three-level atom are calculated exactly without rotating wave approximation. The influence of the binomial light field parameter η on atomic population and quantum entanglement is studied, and the influence of the superposition of atomic energy levels at the initial time on the quantum entanglement is also discussed. Results show that the collapse-revival period of atomic population increases gradually with the increase of η, and the collapse-revival region manifests chaotic characters when η is big enough. In addition, with the increase of η, the periodicity of quantum entanglement evolution gradually disappears, and when the atom is in the excited state at the initial time, the entanglement value at the initial stage and the evolution average value increase gradually, while when the atom is initially in the superposition state, the degree of entanglement decreases gradually. It is also shown that under the non-rotating wave approximation, both of the atomic population probability and the evolution curve of the entanglement between the light field and atom show small sawtooth oscillation.
A new scheme combining controllable quantum teleportation with remote state preparation is proposed to realize two kinds of quantum information communications simultaneously. In the proposed scheme, Alice and Bob are both senders and receivers, and Alice, Bob and Charlie share a nine-qubit entangled state as quantum channel. Under the control of Charlie, Alice can transmit an unknown arbitrary single qubit state to Bob through a series of projection measurement, and meanwhile, Bob can also remotely prepare an arbitrary known two-qubit state to Alice. Compared with other similar hybrid schemes, the state of remote preparation in the proposed scheme is improved from single qubit to two-qubit. Analysis and inference show that the success rate of the proposed scheme is 100%.
For a syetem composed of a pair of V-type three-level atoms in entangled state and a pair of two-mode cavity fields in entangled state, a large detuning interaction between one atom with a cavity field is made to happen during a proper interaction time, so as to realize the entanglement between the atom and the cavity field. The atomic entropy evolution properties of the system are studied, and the influences of the detuning δ on the evolution of atom entropy are discussed by using the quantum entropy theory. The results indicate that δ affects the maximum entanglement value of the entropy and the collapse- recovery phenomenon of atom entropy, and when δ is zero, collapse-recovery phenomenon of atom entropy almost disappears.
Abstract: Rice is one of the main food crops in China, and the detection of heavy metal content is of great significance for its safety and quality. Laser-induced breakdown spectroscopy (LIBS) is expected to overcome the shortcomings of traditional methods for detecting time-consuming and achieve rapid insitu quantitative detection of heavy metals in crop plants such as rice. The collinear double-pulse laser-induced breakdown spectroscopy (DP-LIBS) technique was used to analyze the heavy metal Cd elements in rice leaves. Because different characteristic spectral lines have different effects on the results, in order to obtain more accurate and stable analysis results, the multi-point ablation test method of the sample surface was used to discuss the influence of the three resonance lines of Cd I: 228.8 nm, Cd II: 214.4 nm, and Cd II: 226.5 nm on the coefficient and prediction results of the calibration curve. The comparative study found that the best spectral intensity can be obtained when the 532 nm laser is excited before the 1064 nm laser, and the two pulses have a time interval of 0.5 μs. Among the three analytical lines, the calibration coefficients R2 of Cd I: 228.8 nm, Cd II: 214.4 nm and Cd II: 226.5 nm spectral lines are 0.86, 0.60, and 0.93 respectively, and it is found that the quantitative results of atomic spectral lines are higher than that of the ionic spectral lines. Further study shows that the relative prediction errors of Cd I: 228.8 nm spectral lines are less than 10%, and the detection limit is 3.03 mg/kg. Experiments show that by optimizing the detection conditions of LIBS, the detection of heavy metal contents in rice leaves can be achieved. In addition, the optimized spectral acquisition and characteristic spectral line selection methods in the experiment are also expected to be applied to the detection of heavy metal components in other different agricultural products.
To realize the FPGA on-orbit reconfiguration function of CCD drive circuit of a spaceborne differential absorption spectrometer, an STM32-based ground verification method for on-board reconfiguration of FPGA is proposed. The actual reconfiguration scheme is analyzed and a ground experiment scheme is proposed, then overall scheme is described from two aspects of hardware design and software design. After the test validation in the laboratory environment, it is found that the data sent and read back by the host computer are consistent, and STM32 can simulate the JTAG protocol to load configuration data to the FPGA with reconfiguration time being shortened to 800 ms. The design of hardware and software has been proved to be reasonable and feasible, and can complete the modification of FPGA functions. It is presumed that the solution can provide a reference for FPGA reconfiguration method of CCD driving circuit.
The quantum transport theory of mesoscopic system provides physical model and basis for the design and implementation of quantum devices with excellent performance. By using a transmission matrix method to calculate various transmission coefficients for two-terminal systems based on tight-banding models with fluctuating on-site energies in the scattering region, a two-dimension T-shaped three-terminal quantum dot array model is presented, and then it is reformulated and treated as a standard two-terminal model to study the electron transport of T-shaped quantum dot arrays with asymmetric and symmetric electrodes relative to the middle original point. It is shown that for asymmetric T-shaped quantum dot array, the number of transmission peaks is equal to the number of quantum dots at the input terminal, while for symmetric T-shaped quantum dot array, the number of transmission peaks is equal to the number of quantum dots at the left and right terminal. It is also found that the transmission coefficients are related to the transition integral and the number of quantum dots, but not to the width of quantum dots.