Abstract

Recently, optically encoded second-harmonic generation (SHG) in semiconductor microcrystal lite-doped glasses (SDG) has been observed.¹ The most likely mechanism is the encoding of an effective χ⁽²⁾ due to χ⁽³⁾ of the crystallites and a periodic frozen-in de field. To clarify if this is indeed the case we have studied the properties of the effective χ⁽²⁾ tensor induced during the encoding process. The SDG studied were prepared with linearly polarized fundamental (1064-nm) and second harmonic (532-nm) radiation from a Q-switched Nd:YAG laser producing 8-ns pulses. The glasses were then illuminated with fundamental light polarized linearly with an angle of polarization varied from 0° to 360° relative to the encoding polarization direction. The SHG was analyzed both parallel and perpendicular to the encoding polarization. The measured behavior matches that predicted from internal filled dc field mixing with the χ⁽³⁾ of the crystallites to produce an effective χ⁽²⁾. The influence of the band-gap resonance on χ⁽²⁾ is determined by using glasses with band gaps above and below 532 nm. Since the de field is believed to be caused by electrons swept into surface traps during the encoding process and the ultimate use of these materials will be determined by their stability in optically illuminated conditions, we have measured the intensity and wavelength dependence of optical erasure and in prepared SDG. The results are used to distinguish between erasure by bandgap excitation and trap to conduction band processes.

© 1991 Optical Society of America