Corner Cube Research Articles

Active fiber-based retroreflector providing phase-retracing anti-parallel laser beams for precision spectroscopy.

We present an active fiber-based retroreflector providing high quality phase-retracing anti-parallel Gaussian laser beams for precision spectroscopy of Doppler sensitive transitions. Our design is well-suited for a number of applications where implementing optical cavities is technically challenging and corner cubes fail to match the demanded requirements, most importantly retracing wavefronts and preservation of the laser polarization. To illustrate the performance of the system, we use it for spectroscopy of the 2S-4P transition in atomic hydrogen and demonstrate an average suppression of the first order Doppler shift to 4 parts in 106 of the full collinear shift. This high degree of cancellation combined with our cryogenic source of hydrogen atoms in the metastable 2S state is sufficient to enable determinations of the Rydberg constant and the proton charge radius with competitive uncertainties. Advantages over the usual Doppler cancellation based on corner cube type retroreflectors are discussed as well as an alternative method using a high finesse cavity.

Modelling LARES temperature distribution and thermal drag II: Numerical computation of current-epoch thermal forces

The LARES satellite is a laser-ranged space experiment to contribute to geophysics observation, and to measure the general relativistic Lense-Thirring effect. LARES consists of a solid tungsten alloy sphere, into which 92 fused-silica Cube Corner Reflectors (CCRs) are set in colatitude circles (“rows”). During its first four months in orbit it was observed to undergo an anomalous along-track orbital acceleration of approximately $ -0.4$ pm/s2 $(pm: = picometer)$ . The first paper in this series (Eur. Phys. J. Plus 130, 206 (2015) - Paper I) computed the thermally induced along-track “thermal drag” on the LARES satellite during the first 126 days after launch. The results there suggest that the IR absorbance $ \alpha$ and emissivity $ \epsilon$ of the CCRs equal 0.60, a possible value for silica with slight surface contamination subjected to the space environment. Paper I computed an average thermal drag acceleration of $ -0.36$ pm/s2 for a 120-day period starting with the 7th day after launch. The heating and the resultant along-track acceleration depend on the plane of the orbit, the sun position, and in particular on the occurrence of eclipses, all of which are functions of time. Thus we compute the thermal drag for specific days. The satellite is heated from two sources: sunlight and Earth’s infrared (IR) radiation. Paper I worked in the fast-spin regime, where CCRs with the same colatitude can be taken to have the same temperature. Further, since all temperature variations (temporal or spatial) were small in this regime, Paper I linearized the Stefan-Boltzmann law and performed a Fourier series analysis. However, the spin rate of the satellite is expected currently ( $ \approx$ day 1500) to be slow, of order $ \approx 5$ /orbit, so the “fast-spin equal-temperatures in a row” assumption is suspect. In this paper, which considers epochs up to 1580 days after launch, we do not linearize and we use direct numerical integration instead of Fourier methods. In addition to the along-track drag, this code produces all components of the thermally induced force on the satellite as a function of time throughout the orbit. We find that in the slow spin regime, although there are substantial excursions from the Fourier results, the Fourier results do provide good average values for the temperature of the CCRs (constant temperature in rows from the Fourier method), and for the daily along-track average drag. However, we also find that the relatively small average along-track drag (which swings between $ -0.7$ pm/s2 and $ -0.25$ pm/s2 and averages $ -0.50$ pm/s2 over days 1460-1580) arises from instantaneous accelerations that have excursions that are about an order of magnitude larger than the resulting orbit-averaged drag. Note that neither the first paper nor this one addresses the additional particle drag on the satellite.

A numerical study on nano-indentation induced fracture of low dielectric constant brittle thin films using cube corner probes

In this study, a finite element (FE) model of indentation induced fracture of brittle thin films on tough substrates using the cube corner probes is developed utilising the cohesive zone method. Th...

Fabrication of corner cube array retro-reflective structure with DLP-based 3D printing technology

In this article, the fabrication of a corner cube array retro-reflective structure is presented by using DLP-based 3D printing technology. In this additive manufacturing technology a pattern of a cube corner array is designed in a computer and sliced with specific software. The image of each slice is then projected from the bottom side of a reservoir, containing UV cure resin, utilizing a DLP video projector. The projected area is cured and attached to a base plate. This process is repeated until the entire part is made. The best orientation of the printing process and the effect of layer thicknesses on the surface finish of the cube has been investigated. The thermal reflow surface finishing and replication with soft molding has also been presented in this article.

A study of the micro- and nanoscale deformation behavior of individual austenitic dendrites in a FeCrMoVC cast alloy using micro- and nanoindentation experiments

Micro- and nanoindentation experiments were conducted to investigate the deformation mechanisms in a Fe79.4Cr13Mo5V1C1.6 (wt. %) cast alloy. This alloy consists of an as cast microstructure mainly composed of austenite, martensite, and a complex carbide network. During microhardness testing, metastable austenite transforms partially into martensite confirmed by electron backscatter diffraction. For nanoindentation tests, two different indenter geometries were applied (Berkovich and cube corner type). Load-displacement curves of nanoindentation in austenitic dendrites depicted pop-ins after transition into plastic deformation for both nanoindenters. Characterizations of the region beneath a nanoindent by transmission electron microscopy revealed a martensitic transformation as an activated deformation mechanism and suggest a correlation with the pop-in phenomena of the load-displacement curves. Furthermore, due to an inhomogeneous chemical composition within the austenitic dendrites, more stabilized regions deform by mechanical twinning. This additional deformation mechanism was only observed for the cube corner indenter with the sharper geometry since higher shear stresses are induced beneath the contact area.

Development of a Single-Longitudinal-Mode Ho:YAG Laser Based on Corner Cube**Supported by the National Natural Science Foundation of China under Grant Nos 61308009 and 61405047, the China Postdoctoral Science Foundation Funded Project under Grant No 2013M540288, the Fundamental Research Funds for the Central Universities under Grant Nos HIT.NSRIF.2014044 and HIT.NSRIF.2015042, the Science Fund for Outstanding Youths of Heilongjiang Province under Grant

We present a Tm-doped fiber laser pumped Fabry–Perot etalons Ho:YAG laser based on a corner cube. A maximum single-longitudinal-mode and fundamental transverse mode output power of 478 mW at the wavelength of 2091.06 nm is achieved with a pump power of 16.3 W, corresponding to an optical-to-optical efficiency of 2.9% and a slope efficiency of 7.9%. The single-longitudinal-mode and fundamental transverse mode are less sensitive to the rotating of the corner cube. The results indicate the potential impact of a single-longitudinal-mode Ho:YAG laser with corner cube geometry to improve the anti-maladjustment stability.

System for the measurement of the deviation of a laser beam from the vertical direction.

If a used "vertical beam" is not perfectly vertical in a measurement, a cosine error will be introduced into it. To decrease and compensate for this cosine error, a measurement system is proposed to measure the deviation of the laser beam from the vertical direction. The structure of our measurement system is illustrated, and a model for solving for the deviation angle is established. As the distance of the beam spots on the charge-coupled device is the essential parameter for the measurement results, the acquisition process for this distance is explained. Moreover, the accuracy of the algorithm used in the acquisition process is also tested by experiments. Further, a self-correction module is designed and applied to reduce the error caused by the corner cube reflector in the system. The characteristics of the measurement system such as the resolution, stability, temperature drift, and direction accuracy are analyzed through experiments. The combined uncertainty of the measurement system is calculated to be 11×10-6 rad.

Thermo-optical vacuum testing of Galileo In-Orbit Validation laser retroreflectors

The Galileo constellation is a space research and development program of the European Union to help navigate users all over the world. The Galileo IOV (In-Orbit Validation) are the first test satellites of the Galileo constellation and carry satellite laser retroreflectors as part of their payload systems for precision orbit determination and performance assessment. INFN-LNF SCF_Lab (Satellite/lunar/GNSS laser ranging/altimetry and Cube/microsat Characterization Facilities Laboratory) has been performing tests on a sample of the laser array segment under the Thermo-optical vacuum testing of Galileo IOV laser retro-reflectors of Galileo IOV LRA project, as defined in ESA-INFN Contract No. 4000108617/13/NL/PA. We will present the results of FFDP (Far Field Diffraction Pattern) and thermal relaxation times measurements in relevant space conditions of Galileo IOV CCRs (Cube Corner Retroreflectors) provided by ESA-ESTEC. A reference for the performance of laser ranging on Galileo satellites is the FFDP of a retroreflector in its design specifications and a Galileo retroreflector, in air and isothermal conditions, should have a minimum return intensity within the range [0.55×106m2–2.14×106m2] (ESA-INFN, 2013). Measurements, performed in SCF_Lab facility, demonstrated that the 7 Galileo IOV laser retroreflectors under test were compliant with design performance expectations (Porcelli et al., 2015). The kind of tests carried out for this activity are the first performed on spare Galileo IOV hardware, made available after the launch of the four Galileo IOV satellites (2011 and 2012), which were the operational core of the constellation. The characterisation of the retroreflectors against their design requirements is important because LRAs (Laser Retroreflector Arrays) will be flown on all Galileo satellites.

Variable link equation parameters and expected photon returns for the HartRAO Lunar Laser Ranger - Improving our understanding of the Earth-Moon system

The HartRAO Lunar Laser Ranger (LLR) system requires a state-of-the-art software tool that enables optimal efficiency and signal path parameter estimation. The existing link budget equation estimates the number of returned photons for given conditions and LLR system parameters. This equation is one of the essential mathematical tools that can be considered when developing an integrated system and model for the LLR. The mathematical tool, still under development at HartRAO, can be used to estimate and visualize the relationship between the returned number of photons (observed and computed) and the varying link budget equation parameters. In this work, the tool is used to indicate “worse and optimal” parameter values which influence the return signal, presented as an estimate of expected number of returned photons for the HartRAO station. This is all done to achieve optimal efficiency in the LLR signal path in order to yield an improvement in the return-energy of the laser so that ranges to the lunar corner cube retroreflectors can be measured accurately. The geographic position of the HartRAO station, new state-of-the-art HartRAO LLR system under development and the expected number of returned photons will enable HartRAO to play a key role in improving the ranging accuracy to a sub-centimetre level. This will enhance the current effort to determine highly accurate Earth-Moon distances for various scientific purposes such as Lunar Ephemeris, determination of Universal Time and rate of change of the gravitational constant, G .

Electromagnetic Embossing of Optical Microstructures

Electromagnetic forming (EMF) is a high-speed forming process that is already established in the macroworld. Due to its advantages like high deformation rate and cheaper tools, it is introduced to microforming. In this research, the replication of prismatic optical microstructures is investigated. EN AW-1050A (Al99.5) micrometal sheets with a thickness of 50 μm and 300 μm are electromagnetically micro-embossed. With this technique, it is possible to successfully replicate triangular cross section micro V-grooves of 86.6 μm in width and 24.1 μm in depth with an average surface roughness of Sa = 44 nm. The microstructures of the embossing tool are generated by diamond micro chiseling (DMC), a novel machining process to produce microstructures with discontinuous geometry, like miniature cube corner retro reflectors and V-grooves with well-defined endings.

Reinjection of transmitted laser light into laser-produced plasma for efficient laser ignition.

For improving the laser absorption efficiency in laser ignition, the transmitted laser light was returned to the laser-produced plasma by using a corner cube. In the experiments, the transmitted light was reinjected into the plasma at different times. The laser absorption efficiency was found to be substantially improved when the transmitted light was reinjected into the plasma after adequate plasma expansion. Furthermore, through visualization experiments on gas-dynamics phenomena, it was found that the reinjection of the transmitted light affected not only the laser absorption efficiency but also the gas dynamics after breakdown, and thereby the initial flame kernel development.

Note: Optimal choice of the reflector by phase analysis for heterodyne interferometric roll angle measurement.

The choice of an actual reflector instead of an ideal or perfect reflector has to be dealt with for heterodyne-interferometric roll angle measurement methods. The candidates of regular reflectors such as corner cube prism and right angle prism are analyzed by the homogeneous coordinate transformation method, which provides a theoretical basis for the determination of the actual reflector. Furthermore, the influences of the phase loss of the determined reflector are strictly argued due to non-perfect or natural characteristics itself. Several tactics are considered to solve this problem by phase analysis. By contrast, it is an optimal choice that mirrors-based right angle prism can improve evidently the phase loss by experiment.

Measuring method of diffraction efficiency for plane grating based on Fourier spectral technology.

A traditional double monochromatic measurement instrument of diffraction efficiency for a plane grating involves two major problems: one is the differences of output spectrum bandwidths during measurement of a standard reflection mirror and the tested grating; the other is overlapping of diffracted spectra, which influence testing accuracy of diffraction efficiency. In this paper, a new measuring method of diffraction efficiency based on Fourier spectral technology is presented. The mathematical model of diffraction efficiency is first deduced and then verified by ray tracing and Fourier optics simulation. The influences of the moving cube corner's tilt error, lateral shift error, and maximal moving distance error on the measurement accuracy are analyzed in detail. The analyses provide theoretical references for designing diffraction efficiency instruments. Compared with the traditional diffraction efficiency measurement instrument with double monochromator structure, our method not only improves the measurement accuracy of diffraction efficiency but also has the advantage of high luminous flux, high spectral resolution, multiwavelength measurement in mean time, and high wavenumber accuracy.

Experimental single-photon exchange along a space link of 7000 km

Extending the single photon transmission distance is a basic requirement for the implementation of quantum communication on a global scale. In this work we report the single photon exchange from a medium Earth orbit satellite (MEO) at more than 7000 km of slanted distance to the ground station at the Matera Laser Ranging Observatory. The single photon transmitter was realized by exploiting the corner cube retro-reflectors mounted on the LAGEOS-2 satellite. Long duration of data collection is possible with such altitude, up to 43 minutes in a single passage. The mean number of photons per pulse ({\mu}sat) has been limited to 1 for 200 seconds, resulting in an average detection rate of 3.0 cps and a signal to noise ratio of 1.5. The feasibility of single photon exchange from MEO satellites paves the way to tests of Quantum Mechanics in moving frames and to global Quantum Information.

A numerical study on nano-indentation induced fracture of low dielectric constant brittle thin films using cube corner probes

In this study, a finite element (FE) model of indentation induced fracture of brittle thin films on tough substrates using the cube corner probes is developed utilising the cohesive zone method. The model is specifically applied to brittle low dielectric constant (low-k) thin films and is corroborated by comparison to experimental results. It is shown that the model can decipher mechanisms of radial crack initiation and propagation during loading and unloading phases consistent with experiments. As such, the model lends itself to use as a platform for quantitative and mechanistic understanding of thin film mechanics and characterisation of their fracture properties.

区域观测卫星激光反射器有效反射面积的设计

The structure of laser retro-reflector array dominates the distribution of the effective reflection area and influences the intensity of echo signals. However, for the special purpose of compact experimental satellites the observational activities are only performed in the certain sky region by the ground station. But the laser retro-reflector needs tens of square centimeters of the effective reflection area, and the weight and size are limited. For that the reasonable design of the normal pointing of the cube corners within the retro-reflectors array should be implemented in order to achieve the requirements of large reflection area. The calculation model of the effective reflection area for laser retro-reflector with different normal pointing cube corner was derived and taking laser retro-reflector array designed for one of the regional observational satellites as an example, the simulated calculation and the laboratory test of the effective reflection were given. The results show that the simulations of the effective reflection area of laser retro-reflector for satellite regional observation accord with the testing results. The practicability of the design of laser retro-reflectors for satellite regional observation lays the foundation of its further applications in the future.

区域观测卫星激光反射器有效反射面积的设计

The structure of laser retro-reflector array dominates the distribution of the effective reflection area and influences the intensity of echo signals. However, for the special purpose of compact experimental satellites the observational activities are only performed in the certain sky region by the ground station. But the laser retro-reflector needs tens of square centimeters of the effective reflection area, and the weight and size are limited. For that the reasonable design of the normal pointing of the cube corners within the retro-reflectors array should be implemented in order to achieve the requirements of large reflection area. The calculation model of the effective reflection area for laser retro-reflector with different normal pointing cube corner was derived and taking laser retro-reflector array designed for one of the regional observational satellites as an example, the simulated calculation and the laboratory test of the effective reflection were given. The results show that the simulations of the effective reflection area of laser retro-reflector for satellite regional observation accord with the testing results. The practicability of the design of laser retro-reflectors for satellite regional observation lays the foundation of its further applications in the future.

板ばね研磨による月面反射鏡の平滑加工

板ばね研磨による月面反射鏡の平滑加工

角锥腔固体激光器相干特性的研究

角锥腔固体激光器相干特性的研究

角锥腔固体激光器相干特性的研究

角锥腔固体激光器相干特性的研究