Giant Photoexpansion

Giant photoexpansions produced on a polished surface of a bulk AS2S3 glass. The photograph is taken using a Nomarski interference microscope, and the bar gives 10 pm. 

We here underline that there is an appreciable energy lack of 0.4 eV for [band-to-band) photoelectronic excitation. Nevertheless, the intense Urbach-edge light seems to work as if it were bandgap light. Why  

Another important factor is that the small absorption coefficient, which gives a long penetration depth ( 1 cm) can provide a volumetric effect (Hisakuni and Tanaka, 1994 Tanaka et al, 2006). 

Scalar volume expansions appear also in AgAsS2 when exposed to small [0.2-2 pm in diameter] light spots [Gotoh and Tanaka, 2001a] and to focused electron beams [Yoshida and Tanaka, 1997]. The expansion seems to reflect accumulation of Ag ions through electroionic processes. 

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Hisakuni H. and Tanaka K, Giant photoexpansion in As2S3 glass. Appl. Phys. Lett, 65, 2925-2927 (1994). 

Figure 3.4 Self-aligned microlenses (spherical and aspherical] produced for optical fibers and semiconductor lasers through the giant photoexpansion process.

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