Littrow

Littrow is a surname of Germanic origin. It is associated with the Austrian astronomer Josef von Littrow, who directed the Vienna Observatory in the 19th century. The lunar crater Littrow bears his name in honor of his contributions to astronomy, and the surname appears in several optical and astronomical terms that commemorate his work.

In optics and spectroscopy, Littrow configuration refers to a particular mounting of a diffraction grating in which the incident and diffracted beams share the same optical path. In this arrangement the angle of incidence equals the angle of diffraction, so the light is retroreflected by the grating. The grating equation for the m-th order becomes m λ = 2 d sin i. The Littrow condition, and the corresponding Littrow angle, maximize throughput and simplify instrument geometry, making the configuration common in high-resolution spectrographs, monochromators, and laser-wavelength calibration setups.