Y.J. Choi

PHASE-SHIFTING GRATING PROJECTION MOIRE TOPOGRAPHY

A phase-shifting projection moire´ method particularly intendednfor high-speed three-dimensional inspection of fine objects is presented.nEmphasis is on realization of phase-shifting fringe analysis innprojection moire´ topography using a set of line grating pairs designed tonprovide different phase shifts in sequence. Further, a time-integral fringencapturing scheme is devised to remove undesirable high-frequency originalngrating patterns in real time without time-consuming software imagenprocessing. Finally, the performances of the proposed method are discussednwith measurement results.

Reverse engineering: high speed digitization of free-form surfaces by phase-shifting grating projection moiré topography

Abstract A new digitization method is presented for automatic acquisition of geometric information on free-form surfaces for the sake of reverse engineering. Principles of grating projection moire topography are utilized with emphasis on enhancing the measuring resolution by incorporating phase-shifting fringe analysis. The measuring range and resolution can be readily adjusted to suit the object size to be measured, simply by varying the spatial line pitch of the moire gratings. In addition, no time-consuming beam scanning is required in the measurement, keeping the measuring time relatively low as compared with other existing techniques. Experimental results demonstrate that the three-dimensional coordinate data of 640×480 points can be attained within 5 seconds run on an IBM PC 586, with measuring resolutions of 0.1xa0mm down to 0.001xa0mm.

Two-frequency phase-shifting projection moire topography

Adopting phase-shifting technique in moire topography provides many advantages in measuring complex surface profiles with varying reflectance. However, still the so- called 2(pi) -ambiguity problem remains, which limits the maximum measurable step height difference between two neighboring sample points to be less than half the equivalent wavelength of moire fringes. To cope with the problem in this investigation, a two-wavelength scheme of projection moire topography is proposed along with necessary hardware design considerations. Test results prove that the proposed scheme is capable of finding absolute fringe orders automatically, so that the 2(pi) -ambiguity problem can be effectively overcome so as to treat large step discontinuities in measured surfaces.

Design and implementation of the UFFO burst alert and trigger telescope

The Ultra Fast Flash Observatory pathfinder (UFFO-p) is a telescope system designed for the detection of the prompt optical/UV photons from Gamma-Ray Bursts (GRBs), and it will be launched onboard the Lomonosov spacecraft in 2012. The UFFO-p consists of two instruments: the UFFO Burst Alert and Trigger telescope (UBAT) for the detection and location of GRBs, and the Slewing Mirror Telescope (SMT) for measurement of the UV/optical afterglow. The UBAT isa coded-mask aperture X-ray camera with a wide field of view (FOV) of 1.8 sr. The detector module consists of the YSO(Yttrium Oxyorthosilicate) scintillator crystal array, a grid of 36 multi-anode photomultipliers (MAPMTs), and analog and digital readout electronics. When the γ /X-ray photons hit the YSO scintillator crystal array, it produces UV photons by scintillation in proportion to the energy of the incident γ /X-ray photons. The UBAT detects X-ray source of GRB inthe 5 ~ 100 keV energy range, localizes the GRB within 10 arcmin, and sends the SMT this information as well as drift correction in real time. All the process is controlled by a Field Programmable Gates Arrays (FPGA) to reduce the processing time. We are in the final stages of the development and expect to deliver the instrument for the integration with the spacecraft. In what follows we present the design, fabrication and performance test of the UBAT.

Implementation of the readout system in the UFFO Slewing Mirror Telescope

China Center of Advanced Science and Technology (CCAST);Chinese Academy of Sciences (CAS);Institute of High Energy Physics (IHEP);National Natural Science Foundation of China (NSFC)

THE UFFO SLEWING MIRROR TELESCOPE FOR EARLY OPTICAL OBSERVATION FROM GAMMA RAY BURSTS

While some space born observatories, such as SWIFT and FERMI, have been operating, early observation of optical after grow of GRBs is still remained as an unexplored region. The Ultra-Fast Flash Observatory (UFFO) project is a space observatory for optical follow-ups of GRBs, aiming to explore the first 60 seconds of GRBs optical emission. Using fast moving mirrors to redirect our optical path rather than slewing the entire spacecraft, UFFO is utilized to catch early optical emissions from GRB within 1 sec. We have developed the UFFO Pathfinder Telescope which is going to be on board of the Lomonosov satellite and launched in middle of 2012. We will discuss about scientific potentials of the UFFO project and present the payload development status, especially for Slewing Mirror Telescope which is the key instrument of the UFFO-pathfinder mission.

A next generation Ultra-Fast Flash Observatory (UFFO-100) for IR/optical observations of the rise phase of gamma-ray bursts

The Swift Gamma-ray Burst (GRB) observatory responds to GRB triggers with optical observations in ~ 100 s, butcannot respond faster than ~ 60 s. While some rapid-response ground-based telescopes have responded quickly, thenumber of sub-60 s detections remains small. In 2013 June, the Ultra-Fast Flash Observatory-Pathfinder is expected tobe launched on the Lomonosov spacecraft to investigate early optical GRB emission. Though possessing uniquecapability for optical rapid-response, this pathfinder mission is necessarily limited in sensitivity and event rate; here wediscuss the next generation of rapid-response space observatory instruments. We list science topics motivating ourinstruments, those that require rapid optical-IR GRB response, including: A survey of GRB rise shapes/times,measurements of optical bulk Lorentz factors, investigation of magnetic dominated (vs. non-magnetic) jet models,internal vs. external shock origin of prompt optical emission, the use of GRBs for cosmology, and dust evaporation inthe GRB environment. We also address the impacts of the characteristics of GRB observing on our instrument andobservatory design. We describe our instrument designs and choices for a next generation space observatory as a secondinstrument on a low-earth orbit spacecraft, with a 120 kg instrument mass budget. Restricted to relatively modest mass,power, and launch resources, we find that a coded mask X-ray camera with 1024 cm2 of detector area could rapidlylocate about 64 GRB triggers/year. Responding to the locations from the X-ray camera, a 30 cm aperture telescope witha beam-steering system for rapid (~ 1 s) response and a near-IR camera should detect ~ 29 GRB, given Swift GRBproperties. The additional optical camera would permit the measurement of a broadband optical-IR slope, allowingbetter characterization of the emission, and dynamic measurement of dust extinction at the source, for the first time.

Three-dimensional profile measurement of fine objects by phase-shifting shadow moire interferometry

An industrial application of phase-shifting shadow moire interferometry for automatic 3D inspection of fine objects is presented. A line grating is used to generate shadow type moire fringes whose relative phases are readily determined by implementing the principle of phase shifting so that the surface height of the object can be measured. A special phase-measuring algorithm, named the A-bucket algorithm, is used which can precisely computes the relative phases even though there exists a significant level of errors in phase shifting due to miscalibration and external vibration. Finally, several experimental cases are discussed to demonstrate that a measuring accuracy in the order of 0.001 mm can practically be achieved.

Ultra-Fast Flash Observatory for observation of early photons from gamma ray bursts

We describe the space project of Ultra-Fast Flash Observatory (UFFO) which will observe early optical photons from gamma-ray bursts (GRBs) with a sub-second optical response, for the first time. The UFFO will probe the early optical rise of GRBs, opening a completely new frontier in GRB and transient studies, using a fast response Slewing Mirror Telescope (SMT) that redirects optical path to telescope instead of slewing of telescopes or spacecraft. In our small UFFO-Pathfinder experiment, scheduled to launch aboard the Lomonosov satellite in 2012, we use a motorized mirror in our Slewing Mirror Telescope instrument to achieve less than one second optical response after X-ray trigger. We describe the science and the mission of the UFFO project, including a next version called UFFO-100. With our program of ultra-fast optical response GRB observatories, we aim to gain a deeper understanding of GRB mechanisms, and potentially open up the z<10 universe to study via GRB as point source emission probes.

The slewing mirror telescope of the Ultra Fast Flash Observatory Pathfinder

The Slewing Mirror Telescope (SMT) is a key telescope of Ultra-Fast Flash Observatory (UFFO) space project to explore the first sub-minute or sub-seconds early photons from the Gamma Ray Bursts (GRBs) afterglows. As the realization of UFFO, 20kg of UFFO-Pathfinder (UFFO-P) is going to be on board the Russian Lomonosov satellite in November 2012 by Soyuz-2 rocket. Once the UFFO Burst Alert & Trigger Telescope (UBAT) detects the GRBs, Slewing mirror (SM) will slew to bring new GRB into the SMT’s field of view rather than slewing the entire spacecraft. SMT can give a UV/Optical counterpart position rather moderated 4arcsec accuracy. However it will provide a important understanding of the GRB mechanism by measuring the sub-minute optical photons from GRBs. SMT can respond to the trigger over 35 degree x 35 degree wide field of view within 1 sec by using Slewing Mirror Stage (SMS). SMT is the reflecting telescope with 10cm Ritchey-Chretien type and 256 x 256 pixilated Intensified Charge-Coupled Device (ICCD). In this paper, we discuss the overall design of UFFO-P SMT instrument and payloads development status.