{'fraction_non_alphanumeric': 0.037383177570093455, 'fraction_numerical': 0.004672897196261682, 'mean_word_length': 4.601307189542483, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Holographic phase-conjugation through a sub-wavelength hole

We investigate a holographic lens [1] as an alternative to high-numerical-aperture microscope objectives. For this, the interference pattern of a plane reference beam R and a spherical signal beam S is recorded in an iron-doped lithium niobate crystal utilizing the photorefractive effect [2]. The signal beam is the light being transmitted through a sub-wavelength hole in a gold surface on top of the crystal. For read-out, the phase-conjugated reference beam R* is used, i.e. a plane wave counter propagating to R. The phase-conjugated signal beam S* is reconstructed. This wave is focused onto the sub-wavelength hole. In principle, light coming from all directions behind the hole can contribute to the focusing, and a numerical aperture close to the index of refraction n = 2.3 may result.