  The measurement of the wavelength of light using speckle is a promising tool
for the realization of compact and precise wavemeters and spectrometers.
However, the resolution of these devices is limited by strong correlations
between the speckle patterns produced by closely-spaced wavelengths. Here, we
show how principal component analysis of speckle images provides a route to
overcome this limit. Using this, we demonstrate a compact wavemeter which
measures wavelength changes of a stabilized diode laser of 5.3 am, eight orders
of magnitude below the speckle correlation limit.

Optics;Instrumentation and Detectors