5 Laser Specklometer, Speckle-Optical Diagnostics and Laser …
367
the dependence of correlated intensity functions on movement of the object along
the optical axis are slightly investigated.
The character of speckle decorrelation depends on the way of object movement,
and it will differ from uniform transversal shift [4, 12], longitudinal [13, 14], threedimensional [15] and periodical [5, 16, 17] ones.
Rather effective methods are developed for determination of: (a) transversal velocities due to the measurement of correlation time, shift of peak of correlation function
[18, 19]; (b) amplitude and oscillation frequency due to ratio of harmonics of intensity
fluctuation spectrum of the scattered radiation [20, 21]; (c) longitudinal coordinates
due to interfrequency interval [22]; and (d) velocity of speckle movement [23].
If the diffusive object shifts across the optical axis, then the character of the
formed and time-changing speckle-field depends greatly on conditions of illumination of the diffuser (radius of curvature of the wave front and sizes of laser beam) and
on registration conditions [24–26]. Speckle lifetime is inversely proportional to the
velocity of movement of the diffuser. The speckle lifetime determinates the character
of time correlation function of intensity fluctuation and consequently power spectrum of intensity fluctuations of dynamic speckles connected with it according to
the Wiener–Khinchin theorem. This fact underlies a number of methods of measurement of movement velocity [27, 28]. Much less attention was paid to the fact that
proportionality coefficient depends on longitudinal parameters of the scheme [22].
If the velocity of object movement is known, then determination of proportionality
coefficient gives the possibility to obtain information about longitudinal distances
between the radiator and the diffuser, the diffuser and the observation plane that
is undoubtedly interesting during the development of new methods and devices for
measurements of longitudinal shifts.
Development of holographic and speckle-interferometry [29–34] for determination of shifts [35, 36], elastic responses of biotissues [37, 38], measurements
of velocity of muscle contraction using speckle counting [39], etc., have shown
the possibility and availability of development of new diagnostic coherent-optical
methods and devices in medicine and biology as most objects of the study are
diffusing.
The study of medical–biological objects is connected with great difficulties
comparing to the objects of physical measurements. Mobility, complex structure,
high fault probability, several simultaneous and often uncontrolled processes, bad
repeatability of measurements and other factors cause the necessity of statistical
methods of data processing and establishing correlation connections between the
results of measurements and the functional state of the organism [15, 40, 41]. But due
to contactlessness, non-invasiveness, high sensitivity, objectiveness, possibilities of
speckle-optics do not raise doubts during diagnosing and obtaining new information
about functional state of medical–biological objects [42–45].
First attempts of using laser anemometry [46, 47], optical mixing spectroscopy
[48, 49], holographic methods for creation of archives and pathology classifiers [50],
holographic and speckle-interferometry for studying neuro- and muscular preparations [51, 52], elastic responses of biotissues [53, 54], degree of roughness of human
skin [55], polarization characteristics of radiation scattered by human skin in different
367
the dependence of correlated intensity functions on movement of the object along
the optical axis are slightly investigated.
The character of speckle decorrelation depends on the way of object movement,
and it will differ from uniform transversal shift [4, 12], longitudinal [13, 14], threedimensional [15] and periodical [5, 16, 17] ones.
Rather effective methods are developed for determination of: (a) transversal velocities due to the measurement of correlation time, shift of peak of correlation function
[18, 19]; (b) amplitude and oscillation frequency due to ratio of harmonics of intensity
fluctuation spectrum of the scattered radiation [20, 21]; (c) longitudinal coordinates
due to interfrequency interval [22]; and (d) velocity of speckle movement [23].
If the diffusive object shifts across the optical axis, then the character of the
formed and time-changing speckle-field depends greatly on conditions of illumination of the diffuser (radius of curvature of the wave front and sizes of laser beam) and
on registration conditions [24–26]. Speckle lifetime is inversely proportional to the
velocity of movement of the diffuser. The speckle lifetime determinates the character
of time correlation function of intensity fluctuation and consequently power spectrum of intensity fluctuations of dynamic speckles connected with it according to
the Wiener–Khinchin theorem. This fact underlies a number of methods of measurement of movement velocity [27, 28]. Much less attention was paid to the fact that
proportionality coefficient depends on longitudinal parameters of the scheme [22].
If the velocity of object movement is known, then determination of proportionality
coefficient gives the possibility to obtain information about longitudinal distances
between the radiator and the diffuser, the diffuser and the observation plane that
is undoubtedly interesting during the development of new methods and devices for
measurements of longitudinal shifts.
Development of holographic and speckle-interferometry [29–34] for determination of shifts [35, 36], elastic responses of biotissues [37, 38], measurements
of velocity of muscle contraction using speckle counting [39], etc., have shown
the possibility and availability of development of new diagnostic coherent-optical
methods and devices in medicine and biology as most objects of the study are
diffusing.
The study of medical–biological objects is connected with great difficulties
comparing to the objects of physical measurements. Mobility, complex structure,
high fault probability, several simultaneous and often uncontrolled processes, bad
repeatability of measurements and other factors cause the necessity of statistical
methods of data processing and establishing correlation connections between the
results of measurements and the functional state of the organism [15, 40, 41]. But due
to contactlessness, non-invasiveness, high sensitivity, objectiveness, possibilities of
speckle-optics do not raise doubts during diagnosing and obtaining new information
about functional state of medical–biological objects [42–45].
First attempts of using laser anemometry [46, 47], optical mixing spectroscopy
[48, 49], holographic methods for creation of archives and pathology classifiers [50],
holographic and speckle-interferometry for studying neuro- and muscular preparations [51, 52], elastic responses of biotissues [53, 54], degree of roughness of human
skin [55], polarization characteristics of radiation scattered by human skin in different