Adaptive wavefront sensor based on the Talbot phenomenon

Abstract

A new adaptive method of wavefront sensing is proposed and demonstrated. The method is based on the Talbot self-imaging effect, which is observed in an illuminating light beam with strong second-order aberration. Compensation of defocus and astigmatism is achieved with an appropriate choice of size of the rectangular unit cell of the diffraction grating, which is performed iteratively. A liquid-crystal spatial light modulator is used for this purpose. Self-imaging of rectangular grating in the astigmatic light beam is demonstrated experimentally. High-order aberrations are detected with respect to the compensated second-order aberration. The comparative results of wavefront sensing with a Shack-Hartmann sensor and the proposed sensor are adduced.

Aberration measurements by a Talbot wavefront sensor in the presence of intensity variations

“…even in the presence of high level of amplitude noise. Besides, images do not contain any visible pit displacements as it is seen in the case of phase inhomogeneties [8,24]. On the other hand, pit images contain non constant intensity distributions and this leads to local displacements based on the Eq.…”

Effect of noise and pixel size on the wavefront generated by amplitude holograms

“…To verify the stability of the DOEs to the pixel size (this allows using the amplitude or the phase spatial light modulator (SLM), like in [29], for wavefront generation), a number of holograms were produced witha different step. Fig.…”

“…Despite the LCD dimensions, which are normally larger than the dimension of the CCD, the usage of SLM with the step less than 50 µm does not introduce large errors in the optical wavefront. Besides, the usage of an optical beam compressor [29], which can introduce additional aberrations, is not necessary.…”

Датчик Волнового Фронта Широкоапертурных Лазерных Пучков И Его Применения

“…Поэтому подходы, реализованные, например, в [6,7], даже с учетом современных успехов в создании широкоапертурной оптики из ZnSe и фотоприемников для спектральной области 2−20 µm, приводят к значительному увеличению стоимости прибора, что делает его недоступным для широкого использования. При этом известно, что для контроля волнового фронта мощных широкоапертурных ИК лазеров с успехом может применяться подход, основанный на эффекте Тальбота [8,9]. Эффект Тальбота реализуется на волновых пучках самой различной природы, некоторые примеры представлены в работах [10][11][12].…”