A hand-held optical coagulation sensor, comprising: an assembly including a housing unit that contains a base substrate presenting a first surface with an aperture formed in the first surface of the base substrate, the base substrate being removably reinsertable into the housing unit; a superstrate juxtaposed with the first surface over the aperture to form a closed chamber and prevent access to said chamber through the aperture; and a detector disposed to acquire light scattered, by a medium within the chamber through the superstrate and to provide a data output representing a time series of cross-polarized speckle patterns generated by the medium; and a hand-held data-processing unit that includes electronic circuitry that is in operable communication with the detector and that is programmed to: calculate, based on the data output and using a reflectance standard, a time-averaged total reflectance parameter characterizing the medium; compute, based on the calculated time-averaged total reflectance parameter, a ratio of optical absorption to scattering characterizing the medium; calculate, based on the data output, a speckle autocorrelation curve from time-resolved intensity fluctuations in the speckle patterns; calculate, based on the computed ratio of optical absorption to scattering and on the calculated speckle autocorrelation curve, a mean square displacement associated with optical scatterers of the medium; produce, based on the calculated mean square displacement, an output representing a time-dependent product of a time-dependent effective radius of an optical scatterer of the medium and a viscoelastic modulus of the medium. an assembly including a housing unit that contains a base substrate presenting a first surface with an aperture formed in the first surface of the base substrate, the base substrate being removably reinsertable into the housing unit; a superstrate juxtaposed with the first surface over the aperture to form a closed chamber and prevent access to said chamber through the aperture; and a detector disposed to acquire light scattered, by a medium within the chamber through the superstrate and to provide a data output representing a time series of cross-polarized speckle patterns generated by the medium; a base substrate presenting a first surface with an aperture formed in the first surface of the base substrate, the base substrate being removably reinsertable into the housing unit; a superstrate juxtaposed with the first surface over the aperture to form a closed chamber and prevent access to said chamber through the aperture; and a detector disposed to acquire light scattered, by a medium within the chamber through the superstrate and to provide a data output representing a time series of cross-polarized speckle patterns generated by the medium; and a hand-held data-processing unit that includes electronic circuitry that is in operable communication with the detector and that is programmed to: calculate, based on the data output and using a reflectance standard, a time-averaged total reflectance parameter characterizing the medium; compute, based on the calculated time-averaged total reflectance parameter, a ratio of optical absorption to scattering characterizing the medium; calculate, based on the data output, a speckle autocorrelation curve from time-resolved intensity fluctuations in the speckle patterns; calculate, based on the computed ratio of optical absorption to scattering and on the calculated speckle autocorrelation curve, a mean square displacement associated with optical scatterers of the medium; produce, based on the calculated mean square displacement, an output representing a time-dependent product of a time-dependent effective radius of an optical scatterer of the medium and a viscoelastic modulus of the medium. calculate, based on the data output and using a reflectance standard, a time-averaged total reflectance parameter characterizing the medium; compute, based on the calculated time-averaged total reflectance parameter, a ratio of optical absorption to scattering characterizing the medium; calculate, based on the data output, a speckle autocorrelation curve from time-resolved intensity fluctuations in the speckle patterns; calculate, based on the computed ratio of optical absorption to scattering and on the calculated speckle autocorrelation curve, a mean square displacement associated with optical scatterers of the medium; produce, based on the calculated mean square displacement, an output representing a time-dependent product of a time-dependent effective radius of an optical scatterer of the medium and a viscoelastic modulus of the medium.