A system, comprising: an optical modulator; a local oscillator source configured to provide a reference frequency signal to the optical modulator; an offset source configured to provide an offset frequency signal; a mixer configured to provide a heterodyne signal based on the reference frequency signal and the offset frequency signal; a light source optically coupled to the optical modulator, wherein the light source is operable to emit light so as to illuminate a sample with at least a first portion of the emitted light and illuminate the optical modulator with at least a second portion of the emitted light, wherein the optical modulator is configured to controllably modulate at least the second portion of the emitted light based on the reference frequency signal so as to provide modulated light; an image sensor optically coupled to the sample and the optical modulator, such that the modulated light illuminates the image sensor, wherein the image sensor comprises a plurality of detector elements, wherein each detector element of the plurality of detector elements has a gain input, wherein the gain input is coupled to the mixer such that the gain input of each detector element is modulated based on the heterodyne signal; and a controller comprising at least one processor, wherein the controller is programmed to carry out operations, the operations comprising: adjusting a frequency of the heterodyne signal; while adjusting the frequency of the heterodyne signal, receiving information from the image sensor; and determining a movement of a portion of the sample based on the received information. an optical modulator; a local oscillator source configured to provide a reference frequency signal to the optical modulator; an offset source configured to provide an offset frequency signal; a mixer configured to provide a heterodyne signal based on the reference frequency signal and the offset frequency signal; a light source optically coupled to the optical modulator, wherein the light source is operable to emit light so as to illuminate a sample with at least a first portion of the emitted light and illuminate the optical modulator with at least a second portion of the emitted light, wherein the optical modulator is configured to controllably modulate at least the second portion of the emitted light based on the reference frequency signal so as to provide modulated light; an image sensor optically coupled to the sample and the optical modulator, such that the modulated light illuminates the image sensor, wherein the image sensor comprises a plurality of detector elements, wherein each detector element of the plurality of detector elements has a gain input, wherein the gain input is coupled to the mixer such that the gain input of each detector element is modulated based on the heterodyne signal; and a controller comprising at least one processor, wherein the controller is programmed to carry out operations, the operations comprising: adjusting a frequency of the heterodyne signal; while adjusting the frequency of the heterodyne signal, receiving information from the image sensor; and determining a movement of a portion of the sample based on the received information. adjusting a frequency of the heterodyne signal; while adjusting the frequency of the heterodyne signal, receiving information from the image sensor; and determining a movement of a portion of the sample based on the received information.