A system and technique for monitoring of one or more parameters of a sample are presented. The system comprising: an illumination unit configured for providing coherent illumination of at least two wavelength ranges and for directing said coherent illumination onto an inspection region, and a collection unit configured for collecting light returning from the inspection region and generate one or more image data pieces associated with speckle pattern generated at an intermediate plane between said inspection region and said collection unit. The use of illumination having at least two different wavelength ranges provides generation of speckles associated with mutual- interference of light of the different wavelength ranges, enabling higher efficiency and stability with respect to movement of the inspection region.
