Using phase objects to qualify the transfer function of Fizeau interferometers for high spatial frequencies

Abstract

LIL and LMJ are two French high power laser facilities dedicated to laser-plasma interaction experiments. In order to control the flatness requirements of their optics in a wide spatial periods bandwidth, the CEA has several Fizeau interferometers of different diameters. We use special phase objects to qualify their spatial resolutions. A few papers already dealt with the determination of a Fizeau interferometer transfer function. This was achieved by using either a phase step object or a "virtual" sinusoidal phase object (made of the superposition of two wavefronts with different amplitudes and a small tilt). For practical reasons, we chose to use true sinusoidal phase objects to qualify our instruments. Sinusoidal profiles were then eroded in silica plates. Three different periods are available: 10 mm, 2.5 mm and 1 mm, with two different amplitudes for each period. These phase plates are used to qualify the interferometers performance in terms of spatial resolution in the different configurations (wide or narrow field of view, reflection or transmission) used for LIL/LMJ optics inspection. A comparison to the transfer functions obtained using steps of different widths is also proposed. An experimental verification of the Talbot effect is achieved with the 1-mm plate to investigate propagation effects, as well as contribution of the depth of field.

Measuring a laser focal spot on a large intensity range: effect of optical component laser damages on the focal spot

“…The interferometry result and the direct measurement are very similar up to a ~1 mm radius. We can notice that this is coherent with an interferometer cut-off frequency around 0.7 mm -1 (periods around 1.5 mm) (see [10] for details on interferometer transfer functions). Indeed, a first order approximation can assume that the focal spot is the Fourier transform (plane waves decomposition) of the CPP wavefront.…”

Linear-to-circular polarization conversion with full-silica meta-optics to reduce nonlinear effects in high-energy lasers

“…The transmitted wavefront was measured using a Zygo GPI 4" interferometer equipped with a 1024 × 1024 pixels camera and operating at the wavelength of 1064 nm in linear polarization 61 . The wavefront measurement is carried out with an aperture of 83 mm centered on the clear aperture of the waveplate; polarization is oriented in a vertical or horizontal direction, i.e., along the Oy or Ox axis respectively as depicted in Fig.…”

“…Here, we brought a particular attention to mid-spatial frequencies in the [1-10 mm] period range, which are of major importance for large inertial confinement fusion optics 15,48 . Previous works using calibrated phase plates and detailed elsewhere were carried out to characterize the optical response of the interferometer in terms of RMS and power spectral density in the [1-10 mm] period domain 61 . In addition, one dimensional mean PSD along X xand y axis are computed from the transmitted wavefront maps.…”