Contactless optical extensometer having: a laser beam source for producing a first laser beam and a second laser beam; a first apparatus and a second apparatus for measuring an intensity of a laser beam; wherein the contactless optical extensometer is configured and embodied in that the first laser beam and the second laser beam are brought into interference at an angle (θ) in relation to one another on a surface of a test object, as a result of which an interference fringe pattern is produced on the surface of the test object; in that a first region of the interference fringe pattern is imaged onto the first apparatus for measuring an intensity of the laser beam and a second region of the interference fringe pattern is imaged onto the second apparatus for measuring an intensity of a laser beam, wherein the first region and the second region are disjoint; characterised in that the extensometer has an evaluation device, which is embodied to evaluate a signal of the first apparatus for measuring an intensity of a laser beam and a signal of the second apparatus for measuring an intensity of a laser beam differentially in respect of the frequency and/or the phase, wherein the extensometer further has: a third apparatus for measuring an intensity of a laser beam; a first polarising beam splitter arranged in front of the first apparatus for measuring an intensity of a laser beam, wherein light of a first polarisation of the first region of the interference fringe pattern is imaged onto the first apparatus for measuring an intensity of a laser beam and light of a second polarisation of the first region of the interference fringe pattern is imaged onto the third apparatus for measuring an intensity of a laser beam; a fourth apparatus for measuring an intensity of a laser beam; and a second polarising beam splitter arranged in front of the second apparatus for measuring an intensity of a laser beam, wherein light of a first polarisation of the second region of the interference fringe pattern is imaged onto the second apparatus for measuring an intensity of a laser beam and light of a second polarisation of the second region of the interference fringe pattern is imaged onto the fourth apparatus for measuring an intensity of a laser beam. a laser beam source for producing a first laser beam and a second laser beam; a first apparatus and a second apparatus for measuring an intensity of a laser beam; wherein the contactless optical extensometer is configured and embodied in that the first laser beam and the second laser beam are brought into interference at an angle (θ) in relation to one another on a surface of a test object, as a result of which an interference fringe pattern is produced on the surface of the test object; in that a first region of the interference fringe pattern is imaged onto the first apparatus for measuring an intensity of the laser beam and a second region of the interference fringe pattern is imaged onto the second apparatus for measuring an intensity of a laser beam, wherein the first region and the second region are disjoint; characterised in that the extensometer has an evaluation device, which is embodied to evaluate a signal of the first apparatus for measuring an intensity of a laser beam and a signal of the second apparatus for measuring an intensity of a laser beam differentially in respect of the frequency and/or the phase, wherein the extensometer further has: a third apparatus for measuring an intensity of a laser beam; a first polarising beam splitter arranged in front of the first apparatus for measuring an intensity of a laser beam, wherein light of a first polarisation of the first region of the interference fringe pattern is imaged onto the first apparatus for measuring an intensity of a laser beam and light of a second polarisation of the first region of the interference fringe pattern is imaged onto the third apparatus for measuring an intensity of a laser beam; a fourth apparatus for measuring an intensity of a laser beam; and a second polarising beam splitter arranged in front of the second apparatus for measuring an intensity of a laser beam, wherein light of a first polarisation of the second region of the interference fringe pattern is imaged onto the second apparatus for measuring an intensity of a laser beam and light of a second polarisation of the second region of the interference fringe pattern is imaged onto the fourth apparatus for measuring an intensity of a laser beam. a third apparatus for measuring an intensity of a laser beam; a first polarising beam splitter arranged in front of the first apparatus for measuring an intensity of a laser beam, wherein light of a first polarisation of the first region of the interference fringe pattern is imaged onto the first apparatus for measuring an intensity of a laser beam and light of a second polarisation of the first region of the interference fringe pattern is imaged onto the third apparatus for measuring an intensity of a laser beam; a fourth apparatus for measuring an intensity of a laser beam; and a second polarising beam splitter arranged in front of the second apparatus for measuring an intensity of a laser beam, wherein light of a first polarisation of the second region of the interference fringe pattern is imaged onto the second apparatus for measuring an intensity of a laser beam and light of a second polarisation of the second region of the interference fringe pattern is imaged onto the fourth apparatus for measuring an intensity of a laser beam.