Laser Optical System Research Articles

Realization of single optical frequency laser system for optically pumped cesium beam frequency standards

Compact laser system for optically pumped cesium beam clocks, which use single optical frequency laser for both Cs atomic state preparation and detection, is presented. The saturation probe laser intensity corresponding to certain Cs flux is researched by using laser, locked in the F = 4 → F′ = 4 transition of the Cs D2 line, to interact with Cs atoms. Light shift produced by laser could be reduced when the laser with small intensity, 0.7 mw/cm2, is used to interact with Cs atoms. High efficiency, 70%, fluorescence collectors are installed in the atom–laser interaction region to collect fluorescence. The frequency stability of the laser system is measured by mixing two output laser lights which are locked by fluorescence signal and it is about 3.2 × 10−11 at 2048 s. The compact laser scheme is beneficial to the miniaturization and industrial production of optically pumped Cs beam clocks. The design is also appropriate and useful for other laser frequency stabilization applications.

Half a century of progress in crystal growth of multifunctional borates RAl3(BO3)4 (R = Y, Pr, Sm–Lu)

Investigations of multifunctional RAl3(BO3)4 (R=Y, Pr, Sm–Lu) crystals are divided into three stages: 1962–1972, 1972–1990, 1990 to present, and reviewed step by step. Selective and predominantly unpublished results on high-temperature flux growth (mostly by solution growth on dipped seeds, abbreviated as SGDS method) of these bulk (three-dimensional) crystals and their solid solutions, performed by the author’s research group during last decades, are shortly summarized as well. The pursued studies can be considered as a key base for development of highly efficient optical and new laser systems.

Near diffraction-limited performance of an OPA pumped acetylene-filled hollow-core fiber laser in the mid-IR.

We investigate the mid-IR laser beam characteristics from an acetylene-filled hollow-core optical fiber gas laser (HOFGLAS) system. The laser exhibits near-diffraction limited beam quality in the 3 μm region with M2 = 1.15 ± 0.02 measured at high pulse energy, and the highest mid-IR pulse energy from a HOFGLAS system of 1.4 μJ is reported. Furthermore, the effects of output saturation with pump pulse energy are reduced through the use of longer fibers with low loss. Finally, the slope efficiency is shown to be nearly independent of gas pressure over a wide range, which is encouraging for further output power increase.

A study on laser multi-focus separation technology of thick KDP crystal

KDP crystal is an important electro-optic material in various laser systems, and belongs to very difficult-to-cut material, especially for thick crystals. In this study, an innovative separation method—laser multi-focus separation technology (LMFS) for thick KDP crystal has been developed by skillfully combining femtosecond laser and LMFS optical system of fiber laser for the first time. In this way, the uniformities of temperature and thermal stress distributions along crystal thickness and the utilization efficiency of the laser energy are greatly improved. A penetration crack along crystal thickness could be formed and its propagation direction could be controlled to achieve safe and high-quality separation. The separating thickness of LMFS (50mm) is at least 4 times thicker than that of existing laser separating technologies, and the separating efficiency of LMFS (200µm/s) is at least 20 times faster than that of traditional mechanical methods. The generation mechanism of multi-focus was expounded by optical analysis and design, and verified by an established LMFS optical system. A numerical simulation was also established to analyze the dynamic distributions of temperature and thermal stress of KDP crystal generated by the LMFS optical system, and explore the separation mechanism of LMFS. In addition, a window of appropriate processing parameters was predicted by a series of numerical simulations to successfully separate a thick KDP crystal with the thickness of 50mm. The quality of the separated sidewall surface was clean and flat (roughness of 10.857nm, flatness of 3.5389µm) without any contamination, subsurface damage and edge fragmentation. The experimental results proved the feasibility of LMFS, and are in good agreement with the theoretical analysis.

New generation high performance in situ polarized 3He system for time-of-flight beam at spallation sources.

Modern spallation neutron sources generate high intensity neutron beams with a broad wavelength band applied to exploring new nano- and meso-scale materials from a few atomic monolayers thick to complicated prototype device-like systems with multiple buried interfaces. The availability of high performance neutron polarizers and analyzers in neutron scattering experiments is vital for understanding magnetism in systems with novel functionalities. We report the development of a new generation of the in situ polarized 3He neutron polarization analyzer for the Magnetism Reflectometer at the Spallation Neutron Source at Oak Ridge National Laboratory. With a new optical layout and laser system, the 3He polarization reached and maintained 84% as compared to 76% in the first-generation system. The polarization improvement allows achieving the transmission function varying from 50% to 15% for the polarized neutron beam with the wavelength band of 2-9 Angstroms. This achievement brings a new class of experiments with optimal performance in sensitivity to very small magnetic moments in nano systems and opens up the horizon for its applications.

Five Micron High Resolution MALDI Mass Spectrometry Imaging with Simple, Interchangeable, Multi-Resolution Optical System.

High-spatial resolution mass spectrometry imaging (MSI) is crucial for the mapping of chemical distributions at the cellular and subcellular level. In this work, we improved our previous laser optical system for matrix-assisted laser desorption ionization (MALDI)-MSI, from ~9 μm practical laser spot size to a practical laser spot size of ~4 μm, thereby allowing for 5 μm resolution imaging without oversampling. This is accomplished through a combination of spatial filtering, beam expansion, and reduction of the final focal length. Most importantly, the new laser optics system allows for simple modification of the spot size solely through the interchanging of the beam expander component. Using 10×, 5×, and no beam expander, we could routinely change between ~4, ~7, and ~45 μm laser spot size, in less than 5 min. We applied this multi-resolution MALDI-MSI system to a single maize root tissue section with three different spatial resolutions of 5, 10, and 50 μm and compared the differences in imaging quality and signal sensitivity. We also demonstrated the difference in depth of focus between the optical systems with 10× and 5× beam expanders. Graphical Abstract ᅟ.

INJECTION EFFICIENCY IN COMPTON RING NESTOR

NESTOR is the hard X-ray source that is under commissioning at NSC KIPT. NESTOR based on the Compton scattering of laser photons on relativistic electrons. The structure of the facility can be represented as the following components: a linear accelerator, a transport channel, a storage ring, and a laser-optical system. Electrons are stored in the storage ring for energy of 40-200 MeV. Inevitable alignment errors of magnetic elements are strongly effect on the beam dynamics in the storage ring. These errors lead to a shift of the equilibrium orbit relative to the ideal one. Significant shift of the equilibrium orbit could lead to loss of the beam on physical apertures. Transverse sizes of electron and laser beams are only few tens of microns at the interaction point. The shift of electron beam at the interaction point could greatly complicate the operation adjustment of storage ring without sufficient beam position diagnostic system. This article presents the simulation results of the efficiency of electron beam accumulation in the NESTOR storage ring. Also, this article is devoted to electron beam dynamics due to alignment errors of magnetic element in the ring.

REDESIGN OF NESTOR STORAGE RING LATTICE

NESTOR is the hard X-ray source that is under commissioning at NSC KIPT. NESTOR based on the Compton scattering of laser photons on relativistic electrons. The structure of the facility can be represented as the following components: a linear accelerator, a transport channel, a storage ring, and a laser-optical system. Electrons are stored in the storage ring for energy of 40-225 MeV, laser photons are accumulated in the optical resonator. The frequencies of laser and electron bunches are synchronized, the interaction point located in the optical resonator. The measurements showed that parameters of the manufactured bending magnets different from the design ones. The bending magnets have different field index, besides the vertical focusing forces are significantly lower than designed ones. The beam dynamics simulation showed that due to decreasing of the vertical focusing the vertical betatron frequency becomes close to the frequency of the integer resonance Q = 2, as a result the vertical motion in the ring is unstable [1]. The second reason for optimization is the need to increase the length of the drift space for optical resonator. The results of optimization are presented in this paper.

激光扫描光学断层成像系统的设计与应用

激光扫描光学断层成像系统的设计与应用

Application and Development of Wavefront Sensor Technology

Wavefront sensing technology can directly test the phase distribution of wavefront distortion and has the advantages of simple operation, real-time and large dynamic range. It is widely used in adaptive optics, laser beam quality diagnosis, laser atmospheric communication, optical element and optics system detection, quantitative phase microscope, human eye aberration measurement and other fields. This paper mainly elaborates application and development of wavefront sensing technology in different fields. Combining with the research, wavefront sensing technology is utilized in the high-volume detection of aspherical mobile phone injection and the application advantages in aspheric injection molding lenses error, test efficiency and the number of quality evaluation parameters are illustrated.

One-dimensional magnetic photonic crystal structures with wide absolute bandgaps

The photonic absolute bandgaps have many potential applications in specific fields, and some methods to enlarge the absolute bandgaps, such as adjusting the material and the rotational symmetry, constituting a heterostructure have been explored. Recently, with the occurring of metamaterial, the photonic crystal based on metamaterial has also realized the wide absolute bandgaps. However, the metamaterial is an artificially structured material of which the construction is more complicated. In this paper, one-dimensional magnetic photonic crystal structure with wide absolute bandgaps is proposed, which is composed of two kinds of magnetic materials with the same refractive index and physical thickness but different wave impedances. First of all, the transmission properties of one-dimensional magnetic and non-magnetic photonic crystals with the same wave impedance ratio are studied by using transfer matrix method. It is shown that the normalized frequency bandwidth of magnetic photonic crystal, i. e. the ratio of the band of bandgap to its center, is 0.41, while the normalized frequency bandwidth of the non-magnetic photonic crystal is 0.14. From the results, we can conclude that the absolute bandgap of the above magnetic photonic crystal is wider than that of non-magnetic photonic crystal because the former bandgap is not sensitive to the incident angle nor polarization. Secondly, we adjust the wave impedance ratios of the two kinds of magnetic materials and make them respectively reach 2, 4 and 6, with the refractive index and the physical thickness kept unchanged. By analyzing their transmission properties, it is found that the normalized frequency bandwidths of the absolute bandgaps are respectively 0.47, 0.84 and 1.03, and the greater the difference between the two wave impedances, the wider the normalized frequency bandwidth is. Thirdly, we investigate the influence of the per-layer physical thickness of the magnetic material on the bandgap, with the other parameters remaining unchanged. It is shown that the center of the absolute bandgap shifts toward high frequency with the decrease of the per-layer physical thickness. Finally, a kind of heterostructure is constructed by the above two one-dimensional magnetic photonic crystals. The normalized frequency ranges of the first and the second absolute bandgap of one magnetic photonic crystal structure are respectively 1.18-2.85 and 5.37-6.85. The normalized frequency range of the absolute bandgap of the other magnetic photonic crystal is 2.37-5.68. The normalized frequency range of the absolute bandgap of the heterostructure can be enlarged to 1.18-6.85 and the corresponding normalized frequency bandwidth can reach more than 1.41. The wide absolute bandgaps can be applied to integrated optics, optical fiber communication and high-power laser systems, according to which we may design the polarization-independent and omnidirectional devices such as reflectors, optical switchers and optical filters.

Effect of applied electric field on the chemical structure and thermal diffusion of DLC film irradiated by laser

Diamond-like carbon (DLC) films have attracted much attention because of their excellent performance; however, the low anti-laser damage ability of such films seriously restricts their applicability to high-power infrared optical windows or laser system, etc. To overcome this problem, in this study, Titanium (Ti) electrodes were deposited on DLC films directly, forming a transverse bias field on films' surfaces. The damage morphology under laser irradiation was observed both before and after the bias field was applied, and Raman spectroscopy was used to analyse chemical structure of DLC films. It was shown that as the I(D)/I(G) ratio increased, the sp3 content decreased in laser-irradiated regions of DLC films when a bias electric field was not applied. When the bias electric field was applied to DLC films, it could effectively stop the content changing from sp3-bonding carbon to sp2-bonding carbon, prevent the formation of sp2 clusters, and slow down the films graphitisation process. The fast thermal diffusion improves the DLC films' anti-laser damage ability ultimately.

Effect of applied electric field on the chemical structure and thermal diffusion of DLC film irradiated by laser

Diamond-like carbon (DLC) films have attracted much attention because of their excellent performance; however, the low anti-laser damage ability of such films seriously restricts their applicability to high-power infrared optical windows or laser system, etc. To overcome this problem, in this study, Titanium (Ti) electrodes were deposited on DLC films directly, forming a transverse bias field on films' surfaces. The damage morphology under laser irradiation was observed both before and after the bias field was applied, and Raman spectroscopy was used to analyse chemical structure of DLC films. It was shown that as the I(D)/I(G) ratio increased, the sp3 content decreased in laser-irradiated regions of DLC films when a bias electric field was not applied. When the bias electric field was applied to DLC films, it could effectively stop the content changing from sp3-bonding carbon to sp2-bonding carbon, prevent the formation of sp2 clusters, and slow down the films graphitisation process. The fast thermal diffusion improves the DLC films' anti-laser damage ability ultimately.

Investigation of the effect of passive vortex inserts of different geometrical shapes on the vibrations reduction efficiency in pipelines with two-phase flow

This paper describes the experimental test bench used in coolant flow research with application of adjusted optical laser system. It is based on the technology of pulsed particle visualization of micro tracers, i.e. Particle Image Velocimetry (PIV system) that allows for the analysis of the microstructure of the hydrodynamic liquid flow passed through the vortex inserts. Optical measurement (PIV-method) of hydro- and aerodynamic characteristics of the coolant flow allowed obtaining the velocity distribution in straight and various curved sections of the pipeline in order to reliably define the vortex formation condition and the occurrence of the pressure gradient on the outer and inner walls of the curved sections. This gives us the opportunity to verify the calculation models describing the problem of passive control (decrease) of the displacement of pipelines of power equipment, and thus to improve the reliability and safe operation of the system in general.

Understanding Hybrid Additive Manufacturing of Functional Devices

The fabrication of electronic components in three-dimensional space is critical for building multifunctional devices. Traditional manufacturing approaches are limited to building planar device configurations. In order to address this limitation, our group has developed a novel hybrid additive manufacturing process that can deposit multi-material patterns on conformal substrates. This direct-write approach involves the combination of microextrusion, pico jet and laser systems. A multi-axis robot was employed to deposit slurries and colloids of conductive materials on different substrates. Fine deposition of the slurries was achieved by tuning the process parameters such as deposition line speed, extrusion pressure, curing temperature, Z-height, laser beam spot, material type and laser intensity. Precise deposition of the medium viscous colloidal liquids was achieved by pico jet unit. Sintering of the micro/nano particles was achieved using a fiber optic laser system and micro wave furnace. The conductance of the deposited electrical trace varied based on the material type and trace cross-section area. This research lays the foundation to build a three-dimensional hierarchy of electronic components. By embedding components at various depths and orientations complex electronic circuitry with versatile material compositions and design flexibility can be fabricated in situ.

Versatile optical laser system for experiments at the European X-ray free-electron laser facility.

We present the main features of the final prototype of a pulsed optical laser, developed for pump-probe and other experiments in conjunction with the femtosecond x-ray beams at the European X-ray free-electron laser facility. Adapted to the temporal x-ray emission pattern of the facility, the laser provides 10 Hz bursts of up to 600 µs duration with intra-burst pulse frequencies as high as 4.5 MHz. In this mode, we have generated pulses as short as 12 fs at 350 W average power during the burst and with beam qualities close to the diffraction limit. This is, to the best of our knowledge, the highest power to date of a few-cycle laser operating at a center wavelength of 800 nm. Important for experimental flexibility, the laser can be configured in various unique ways, enabling, e.g., energy scaling to >3 mJ per pulse through a frequency change down to 100 kHz and the generation of nearly transform limited pulses between 12 fs and 300 fs. In addition to the 800 nm femtosecond beam line, a synchronized long pulse (0.8 ps or 400 ps) 1030 nm beam can be utilized, offering up to 4 kW burst average power, i.e. up to 40 mJ per pulse at 100 kHz. Efficient nonlinear wavelength conversion and tuning through intrinsic and external means further enhance the capabilities of the laser.

Effects of photobiomodulation therapy (PBMT) on bovine sperm function.

Fertilization rates and subsequent embryo development rely on sperm factors related to semen quality and viability. Photobiomodulation therapy (PBMT) is based on emission of electromagnetic waves of a laser optical system that interact with cells and tissues resulting in biological effects. This interaction is mediated by photoacceptors that absorb the electromagnetic energy. Effects are dependent of irradiation parameters, target cell type, and species. In sperm, PBMT improves several features like motility and viability, affecting sperm aerobic metabolism and energy production. The aim of this study was to investigate, under same conditions, how different output powers (5, 7.5, and 10mW) and time of irradiation (5 and 10min) of laser (He-Ne laser, 633nm) may affect frozen/thawed bovine sperm functions. Results showed significant effects depending on power while using 10min of irradiation on motility parameters and mitochondrial potential. However, no effect was observed using 5min of irradiation, regardless of power applied. In conclusion, PBMT is effective to modulate bovine sperm function. The effectiveness is dependent on the interaction between power applied and duration of irradiation, showing that these two parameters simultaneously influence sperm function. In this context, when using the same fluency and energy with different combinations of power and time of exposure, we observed distinct effects, revealing that biological effects should be also based on simple parameters rather than only composite parameters such as fluency, irradiance and energy. Laser irradiation of frozen/thawed bovine semen led to an increase on mitochondrial function and motility parameters that could potentially improve fertility rates.

MOBILE MAPPING BY FMCW SYNTHETIC APERTURE RADAR OPERATING AT 300 GHZ

While optical cameras or laser systems are widely used for mobile mapping low attention was payed for radar systems. Due to new semiconductor technologies, compact and leight weight SAR systems based on the Frequency Modulated Continuous Wave (FMCW) principle in the millimeter wave domain can serve for mobile radar mapping on cars. For mapping of long stripes along roads in close range a special strategy for focusing of SAR images was developed. Hereby local adapted planes for processing are used considering the IMU data of the sensor. An experimental system was designed for high resolution radar mapping of urban scenes in close range geometry. This small and leight weighted system has a bandwidth of 30 GHz (5 mm resolution) and operates with 300 GHz in the lower terahertz domain. Experiments with a van in an urban scenario were carried out for proof of applicability of an operating SAR system resolving objects in the subcentimeter domain. The results show that narrow cracks in the asphalt of the road are visible and the measuring of small metallic objects placed in the scene is possible. Based on this mobile mapping techniques a first result from an acquisition of vertical facade structure is shown.

MOBILE MAPPING BY FMCW SYNTHETIC APERTURE RADAR OPERATING AT 300 GHZ

Abstract. While optical cameras or laser systems are widely used for mobile mapping low attention was payed for radar systems. Due to new semiconductor technologies, compact and leight weight SAR systems based on the Frequency Modulated Continuous Wave (FMCW) principle in the millimeter wave domain can serve for mobile radar mapping on cars. For mapping of long stripes along roads in close range a special strategy for focusing of SAR images was developed. Hereby local adapted planes for processing are used considering the IMU data of the sensor. An experimental system was designed for high resolution radar mapping of urban scenes in close range geometry. This small and leight weighted system has a bandwidth of 30 GHz (5 mm resolution) and operates with 300 GHz in the lower terahertz domain. Experiments with a van in an urban scenario were carried out for proof of applicability of an operating SAR system resolving objects in the subcentimeter domain. The results show that narrow cracks in the asphalt of the road are visible and the measuring of small metallic objects placed in the scene is possible. Based on this mobile mapping techniques a first result from an acquisition of vertical facade structure is shown.

Study on cooling of positronium for Bose–Einstein condensation

A proposed new method of cooling positronium is to realize the Bose–Einstein condensation (BEC) of positronium. We perform detailed studies of three processes: (1) thermalization processes between positronium and the silica walls of a cavity, (2) Ps–Ps scattering and (3) laser cooling. The thermalization process is shown to be not sufficient for BEC. Ps–Ps collision is shown to have a big effect on the cooling performance. We combine both methods and establish an efficient cooling process for BEC. We also propose a new optical laser system for the cooling.