As a part of the work carried out on a project supported by the Danish council for technology and innovation, we have investigated the option of smoothing standard CNC machined surfaces. In the process of constructing optical prototypes, involving custom-designed optics, the development cost and time consumption can become relatively large numbers in a research budget. Machining the optical surfaces directly is expensive and time consuming. Alternatively, a more standardized and cheaper machining method can be used, but then the object needs to be manually polished. During the polishing process the operator needs information about the RMS-value of the surface roughness and the current direction of the scratches introduces by the polishing process. The RMS-value indicates to the operator how far he is from the final finish, and the scratch orientation is often specified by the customer in order to avoid complications during the casting process.
In this work we present a method for measuring the RMS-values of the surface roughness while simultaneously determining the polishing direction. We are mainly interested in the RMS-values in the range from 0 – 100 nm, which corresponds to the finish categories of A1, A2 and A3. Based on simple intensity measurements we estimates the RMS-value of the surface roughness, and by using a sectioned annual photo-detector to collect the scattered light we can determine the direction of polishing and distinguish light scattered from random structures and light scattered from scratches.
The catastrophic optical mirror damage (COMD) effect is analyzed for 808 nm emitting diode lasers in single-pulse
operation. During each single pulse, both nearfield of the laser emission and thermal image of the laser facet are
monitored with cameras being sensitive in the respective spectral regions. A temporal resolution in the μs-range is
achieved. The COMD is unambiguously related to the occurrence of a 'thermal flash' detected by thermal imaging. A
one-by-one correlation between emission nearfield, 'thermal flash', thermal runaway, and structural damage is observed.
As a consequence of the single-pulse-excitation technique, the propagation of 'dark bands' as observed in photo- or
cathodoluminescence maps in the plane of the active region from the front facet is halted after the first pulse. Because of
the rapidness of the thermal runaway, we propose the single-pulse technique for testing the facet stability and the
intentional preparation of early stages of COMD; even for diode lasers that regularly fail by other mechanisms.
KEYWORDS: Doppler tomography, Optical coherence tomography, Heart, Signal processing, Electronic filtering, Linear filtering, Field programmable gate arrays, Signal analyzers, In vivo imaging, Optical filters
We demonstrate a field programmable gate-array-based real-time optical Doppler tomography system. A complex-valued bandpass filter is used for the first time in optical coherence tomography signal processing to create the analytic signal. This method simplifies the filter design, and allows efficient and compact implementation by combining the conversion to an analytic signal with a pulse shaping function without the need for extra resources as compared to the Hilbert transform method. The conversion of the analytic signal to amplitude and phase is done by use of the coordinate rotation digital computer (CORDIC) algorithm, which is an efficient algorithm that maps well to the field programmable gate array. Flow phantom experiments, and the use of this system for in vivo imaging of cardiac dynamics in the chick embryo, are presented. We demonstrate the visualization of blood flow in the early embryonic heart as well as in the aorta, small peripheric vitelline vessels, and coronary arteries of fully formed chick hearts.
We investigate vascular changes during Photodynamic therapy (PDT) of skin tumors using optical Doppler tomography
(ODT). The effect of vascular shut down on tumor destruction is currently not known, and to optimize treatment it is
relevant to investigate this issue further. Optical Doppler tomography is capable of measuring blood flow in biological
tissue down to 1-2 mm with sub-mm/s velocity sensitivity and micrometer spatial resolution making it suitable for blood
flow measurements in the skin. We demonstrate the ability of detecting blood flow in the human skin using non-interstitial
ODT to preserve the non-invasiveness. In general a very limited blood flow activity was observed in normal
skin and around skin tumors making monitoring of changes difficult. We suggest solutions to a number of practical
issues such as sampling errors and natural fluctuations in flow activity for future work.
One of the most critical but poorly understood processes during cardiovascular development is the establishment of a
functioning coronary artery (CA) system. Due to the lack of suitable imaging technologies, it is currently impossible to
visualize this complex dynamic process on living human embryos. Furthermore, due to methodological limitations, this
intriguing process has not been unveiled in living animal embryos, too. We present here, to the best of our knowledge,
the first in vivo images of developing CAs obtained from the hearts of chick embryos grown in shell-less cultures. The
in vivo images were generated by optical coherence tomography (OCT). The OCT system used in this study is a mobile
fiber-based time-domain real-time OCT system operating with a center wavelength of 1330 nm, an A-scan rate of 4
kHz, and a typical frame rate of 8 frames/s. The axial resolution is 17 &mgr;m (in tissue), and the lateral resolution is 30 &mgr;m.
The OCT system is optimized for in vivo chick heart visualization and enables OCT movie recording with 8 frames/s,
full-automatic 3D OCT scanning, and blood flow visualization, i.e., Doppler OCT imaging. Using this OCT system, we
generated in vivo OCT recordings of chick embryo hearts to study the process of connection of the future right coronary
artery (RCA) to the aorta. Recordings were made at three critical stages during development: day 8 (no clear connection
yet), day 9 (established connection of RCA with the aorta with clear blood flow) and day 10 (further remodeling of the established RCA).
We present a compact, non-contact, low-cost optical sensor for real time vibration detection and active vibration control
of mechanical devices based on laser speckle translation. The speckle translation is processed optically with a narrow
spatial filter to provide electrical signals carrying in-phase and phase quadrature information about the speckle motion.
The optical sensor is integrated with an ASIC. The ASIC and an external programmable logical device (PLD) calculate a
real time electrical error signal, which then is fed back a piezo-electrical crystal. For testing purposes a mechanical
sinusoidal vibration is applied to the target via a piezo-electrical spacer. The error signal deforms the piezo-electrical
spacer in order to counteract and minimize the vibrational motion of the target. The primary purpose of this work is to
demonstrate the feasibility of producing a compact, low-cost sensor that carries out single-point measurement of submicron,
in-plane translational vibration of a solid structure in real time.
Proc. SPIE. 5690, Coherence Domain Optical Methods and Optical Coherence Tomography in Biomedicine IX
KEYWORDS: Optical filters, Digital signal processing, Optical coherence tomography, Field programmable gate arrays, Linear filtering, Signal processing, Analog electronics, Electronic filtering, Doppler tomography, Bandpass filters
We report the design of and results obtained by using a Field Programmable Gate Array (FPGA) to digitally process Optical Doppler Tomography signals. The processor fits into the analog signal path in an existing OCT setup. We demonstrate both Doppler frequency and envelope extraction using the Hilbert transform, all in a single FPGA. An FPGA implementation has certain advantages over a general purpose Digital Signal Processor (DSP) due to the fact that the processing elements operate in parallel as opposed to the DSP, which is primarily a sequential processor.
In this paper, we demonstrate that the use of a FPGA enables sampling rates exceeding DSP-based solutions. In addition, this implementation has the important feature that calculation of the phase in addition to the amplitude of the interference fringe pattern only requires few additional resources. The proposed implementation of Doppler frequency extraction in a single FPGA is feasible for real-time Doppler OCT applications requiring high signal sampling rates.
We present a compact, low-cost optical method for detection of in-plane speckle translation, which e.g. could be a measure of in-plane translation or rotation of a solid structure. The speckles are produced by illuminating a non-specular target surface with coherent light. The scattered light propagates through free-space to the sensor inlet. The sensor is based on a lenticular array, which implements a narrow spatial band-pass filter, acting on the translating speckle patterns. The sensor detects speckle translation, which for the given configuration can be caused to detect both translation and rotation of the target. The presented free space propagation design can provide a sensor with no direct sensitivity on the working distance. The electrical signals from the sensor are processed with a digital algorithm, based on zero-crossings detection to provide real-time displacement measurements. The spatial filter of the sensor is characterized here, and the precision of the sensor, integrated with a processor, which applies zero-crossing detection to the signal, is considered.