  We present a proposal of a set-up to measure the work distribution due to an
arbitrary unitary process acting on the spatial transverse degrees of freedom
of a light beam. Hermite-Gaussian optical modes representing a quantum harmonic
oscillator are prepared in a thermal state and sent through an interferometer.
We show that the Fourier transform of the work distribution, or the
characteristic function, can be obtained by measuring the intensity at the
output of the interferometer. The usefulness of the approach is illustrated by
calculating the work distribution for a unitary operation that displaces the
linear momentum of the oscillator. We discuss the feasibility of the
experiment, which can be realized with simple linear optical components.
