9. Conclusion

On the basis of the model accounting interference of multiple waves with random phases a relation between phase dynamics of the waves sounding a thin transparent object and the speckle dynamics in the object image plane was detected theoretically. General-case formulas were obtained to determine the dependence of time-average intensity ~I and temporal autocorrelation function η ¼ ηðtÞ of this intensity at some point in the image plane with mean value 〈x〉, mean square deviation σu, and correlation time τ<sup>0</sup> of optical path difference Δu of wave pairs in the neighborhood of the conjugate point of the object plane. The diameter of this neighborhood equals the linear resolution of the lens that generates the object image. Relation between the temporal spectral function of a random process ΔuðtÞ and a similar function of the process <sup>~</sup>Iðt<sup>Þ</sup> was substantiated.

An optical device relevant to the model used in the theory was developed.

Very good coincidence between the theory and the experiment has been demonstrated by batched random variation of path difference Δu. The procedure of calibrating the optical device for determination of σ<sup>u</sup> was developed; its errors and the sensitivity limit of the technique were assessed.

Biological objects in the form of a live cell monolayer on a transparent substrate in a thin cuvette with nutrient solution were used to substantiate application of value σ<sup>u</sup> as a cell activity parameter.

It was shown that the technique allows detection of herpes virus in cells as early as 10 min from the experiment start.

Rapid assessment of cell reaction to toxic substances therapeutic management of antibacterial and antiviral drugs can be the nearest perspective for application of the technique. Development of a technique for simultaneous determination of values 〈x〉, σu, and τ<sup>0</sup> in different parts of an individual cell can become a line of further research.
