Single-shot phase detection in a speckle wavemeter for the measurement of femtometric wavelength change

An optical system with instantaneous phase detection is proposed for wavelength change detection in the femtometre scale. Phase measurements are achieved within a few tens of femtometres using a custom made Integrating Sphere (IS) with temperature control. The phase is detected in a single-shot of speckle patterns that are produced using light from a tunable laser after multiple reflections in an IS and combined with a reference beam. It is shown that the proposed optical system produces fringe patterns with phase that is as sensitive as a Wavelength Scanning Interferometer (WSI), with similar optical path difference corresponding to the diameter of the IS. The interference patterns produced by the optical setup show some areas of the interferogram with phase sensitivities that are analogous to the WSI interference, and other areas were vortex generation and annihilation appear independently. Depending on the phase spatial distribution and sensitivity, it is shown here that the phases without vortices can be used to identify particular wavelengths within the femtometre resolution, therefore the sub-femtometer resolution can be attributed to the vortices creation and annihilation.