A differential fiber-optic confocal microscope, comprising: an illumination system; a first single-mode optical fiber arranged with an end adapted to be optically coupled to said illumination system to receive illumination radiation from said illumination system; a fiber coupler adapted to be optically coupled to a second end of said first single-mode optical fiber; a second single-mode optical fiber having an end adapted to be optically coupled to said fiber coupler; a sample support stage arranged to receive illumination radiation from a second end of said second single-mode optical fiber; a third single-mode optical fiber having an end adapted to be optically coupled to said fiber coupler; a detector arranged to receive output radiation from a second end of said third single-mode optical fiber, the output radiation having a detected frequency; characterized in that said differential fiber-optic confocal microscope furthermore comprises: a stage assembly operatively coupled to said sample support stage, said stage assembly being structured to move said support stage by incremental steps in three different linear directions toward and away from said second end of said second single-mode optical fiber; a lock-in amplifier electrically connected to said detector and said illumination system, whereby the lock-in amplifier correlates a time-varying strength of the illumination system with the detector by matching a frequency of the illumination radiation with the detected frequency; and a computer in communication with said lock-in amplifier, and said stage assembly, wherein said computer is programmed to move said sample support stage to a position along at least one of said three different linear directions of motion of said sample support stage toward and away from said second end of said second single-mode optical fiber, whereby observations are made outside of a diffraction-limited region of optical response of said differential confocal microscope. an illumination system; a first single-mode optical fiber arranged with an end adapted to be optically coupled to said illumination system to receive illumination radiation from said illumination system; a fiber coupler adapted to be optically coupled to a second end of said first single-mode optical fiber; a second single-mode optical fiber having an end adapted to be optically coupled to said fiber coupler; a sample support stage arranged to receive illumination radiation from a second end of said second single-mode optical fiber; a third single-mode optical fiber having an end adapted to be optically coupled to said fiber coupler; a detector arranged to receive output radiation from a second end of said third single-mode optical fiber, the output radiation having a detected frequency; characterized in that said differential fiber-optic confocal microscope furthermore comprises: a stage assembly operatively coupled to said sample support stage, said stage assembly being structured to move said support stage by incremental steps in three different linear directions toward and away from said second end of said second single-mode optical fiber; a lock-in amplifier electrically connected to said detector and said illumination system, whereby the lock-in amplifier correlates a time-varying strength of the illumination system with the detector by matching a frequency of the illumination radiation with the detected frequency; and a computer in communication with said lock-in amplifier, and said stage assembly, a stage assembly operatively coupled to said sample support stage, said stage assembly being structured to move said support stage by incremental steps in three different linear directions toward and away from said second end of said second single-mode optical fiber; a lock-in amplifier electrically connected to said detector and said illumination system, whereby the lock-in amplifier correlates a time-varying strength of the illumination system with the detector by matching a frequency of the illumination radiation with the detected frequency; and a computer in communication with said lock-in amplifier, and said stage assembly, wherein said computer is programmed to move said sample support stage to a position along at least one of said three different linear directions of motion of said sample support stage toward and away from said second end of said second single-mode optical fiber, whereby observations are made outside of a diffraction-limited region of optical response of said differential confocal microscope.