ABSTRACT The laser Doppler velocimeter was developed specially for students laboratory training. The experimental kit consists of the classic dual beam laser Doppler system and the set of the dynamic objects such as moving phase screen and scattering flows. Signal processing and data analysis is performed using personal computer that allows for flexible training

Alexey S Kurtov

Boris L Djagilev

Ivan V Fedosov

Valery V Tuchin

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Laser Doppler velocimeter for laboratory training
ivan V. Fedosov*, Boris L. Djagilev, Alexey S. Kurtov, Valery V. Tuchin
Saratov State University, REC-006, Laboratory of biophotonics.
ABSTRACT
The laser Doppler velocimeter was developed specially for students laboratory training. The experimental kit consists of the
classic dual beam laser Doppler system and the set of the dynamic objects such as moving phase screen and scattering
flows. Signal processing and data analysis is performed using personal computer that allows for flexible training.
Keywords: speckles, blood flow
1. INTRODUCTION
Optical education in the century of hi-tech instrumentation has to reveal the interrelations between optics and different
branches of sciences and the principles of optical instrumentation design for students. Practical training is the shortest way
to demonstrate to students the interrelations between the fundamental principles and its real world applications. At present
laser Doppler anemometry is one of well developed and useful instrument with wide range of applications' . Laser Doppler
velocimeters (LDV) are used for supersonic flow investigation, for multicomponent flow analysis2. in i'ii'o hioflow
monitoring3 etc. LDV is based Ofl the fundamental principles of the modern optics such coherence, Doppler effect, light
scattering and diffraction. In one hand, practical work with the simplest LDV will illustrate these principles, will enable
students to understand the principles of optical instrumentation design. In other hand such simple device is a useful
instrument for practical investigation of flow structure that will allow for students to arrange its research works in
mechanics and biophysics. LDV is one of examples of interrelations between different branches of modern physics.
Moreover the flexible signal processing using personal computer illustrates the principles of digital signal processing and
analysis.
Our main idea is to develop the basic kit of instruments to provide the wide range of practical works on optics, fluid
mechanics, biophysics, engineering and digital signal processing. In present paper the ideology of such kit is described and
illustrated with the first result obtained with our first prototype. The examples of practical tasks are proposed and discussed.
2. BASIC KIT
This practical work will enable student to: understand principles of optical heterodyning; understand principles of digital
signal processing; get an overview ofprinciples and schemes for basic laser instruments such LDV. Basic kit consists on the
simple dtal beam LDV designed for forward scattering geometry; positioning stage with micrometer screw; frozen glass
rotating disc with motor drive; set of transparent tubes and scattering suspension. The main component of basic kit is the
LDV setup that is shown on fig. 1 . Coherent collimated light beam from 1 mW laser diode module is divided with
wavefront splitter and resulting beams are focused into the tube or on the glass disc surface and forms the sensitive olume.
Angle between crossed beams is 10 deg. Scattered light is collected on the photodiode and non-scattered light is blocked
with beam stops. Objectives working distances are 67 mm. The optical components are mounted on the steel plate.
Photocurrent signal is amplified and digitized with standard PC sound card. Photocurrent amplifier output is designed for
sound card to minimize the cost of educational set up. The further signal processing is performed using standard or
customized software and allows for different kind of work. The additional equipment is mounted on the micropositioning
stage. Motorized frozen glass disc of 14 mm in diameter is driven with variable DC voltage 0 —24 volts. The results of
spectrum analysis of the photocurrent signal obtained when frozen glass disc is placed in the sensitive volume of the LDV
is shown on the figure 2.
*
FedosovIVinfo.sgu.ru; phone: 7(8452)51-51-95; Saratov State University. Dept. of Optics, 155, Moskovskaya, 410026 Saratov.
Russia.
Seventh International Conference on Education and Training in Optics and Photonics,
Tuan-Kay Lim, Arthur H. Guenther, Editors, Proceedings of SPIE Vol. 4588 (2002)
© 2002 OSA and SPIE · 0277-786X/02/$15.00
507
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Fig. 2. Doppler frequency shift power spectrum obtained with rotating frozen glass disk.
3. EXAMPLES OF TASKS FOR STUDENTS
The developed kit allows for different kinds oftasks for students.
The simplest work is the investigation of the LDV properties. This work includes the following tasks: to calculate the
relation ofthe object velocity and Doppler frequency shift at known scattering geometry; to measure velocity offrozen glass
disc surface for different voltage on disc driver using two methods: LDV and direct measurements of rotation period and
disc radius for different; to analyze the correlation between two resulting data sets. The additional task is to measure the
length of LDV sensitive volume using rotating disk placed on the micropositionning stage or to investigate the case when
the disc surface is not perpendicular to the optical axe of the instrument and to check the property of to measure velocity
projection on the vector of sensitivity4.
Another kind of work is the investigation of flow and bioflow dynamics. Such research includes the following tasks: to
determine the velocity distribution across the flow in tube; to investigate the flow velocity distribution for liquids with
different viscosity at fixed pressure difference on the edges of tube. The additional task for students of biomedical
specialization is the investigation ofwhole blood flow as the flow ofnon-Newtonian liquid.
The third group ofpractical tasks is the investigation ofdigital signal processing principles and development ofsoftware for
the computer assisted experimental setup. LDV is used as a source of real signal. Typical tasks of this group are: the digital
filtering algorithm comparison; digital spectrum analysis ofstochastic signal; automatic velocity monitoring.
'
-I
Fig. 1 . Laser Doppler velocimeter
Proc. SPIE Vol. 4588508
4 CONCLUSION
The universal LDV for practical works is developed to support different kinds of courses on optics; optical instrumentation
and measurements; fluid mechanics; digital signal processing. Moreover such device is the useful laboratory instrument for
student's scientific research support. The basic kit is designed for use with standard PC with minimal system requirement
and contains no one costly component.
5. ACKNOWLEGEMENTS
This work is supported U. S. Civilian Research & Development Foundation for the Independent States of the Former Soviet
Union, Award NREC-0O6.
6. REFERENCES
1. C. Tropea, "Laser Doppler anemometry: recent develoments and future challenges," Meas Sci. Technol. 6, pp. 605-619,
1995.
2. F. Durst, G. Brenn, T.H. Xu, "A review of the development and characteristics of planar phase - Doppler anemometry,"
Meas. Schi. Technol., 8, pp. 1203-1221, 1997.
3. T. Eiju, M. Nagai, K. Matsuda, J. Ohtsubo, K. Homma, K. Shimizu, "Microscopic laser Doppler Velocimeter for blood
velocity measurement," Opt. Eng., Vol. 32, No. 1, pp. 15-20.
4. B. S. Rinkevitchus, Laser diagnostics qfflows, Moscow Institute of Energetic Engineering Press, Moskow, 1990.
Proc. SPIE Vol. 4588 509


Laser Doppler velocimeter for laboratory training

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Laser Doppler velocimeter for laboratory training

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