Polarization Dependence of Photoinduced Birefringence in Chalcogenide Thin Film

• Published in: Japanese Journal of Applied Physics Vol. 40; no. 6R; pp. 3965 - 3968
• Main Authors: Lee, Hyun-Yong, Jang, Sun-Joo, Kim, Eun-Soo, Chung, Hong-Bay
• Format: Journal Article
• Language: English
• Published: 2001
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.40.3965

Polarization dependence of photoinduced birefringence has been investigated in an amorphous As–Ge–Se–S chalcogenide thin film using two 632.8 nm HeNe lasers (inducing and probing beams), which have a lower energy than the optical energy gap ( E OP ) of the film, that is, an exposure to sub-band gap light ( h v < E OP ). The polarization states of the inducing beam are controlled using a pair of phase retarder and linear polarizer to obtain linearly, circularly and elliptically polarized light beams. In addition, the kinetics of photoinduced dichroism has also been studied. The amplitudes of dichroism ( D ) and birefringence ( Δ n ) increase with increasing induction time and eventually both are saturated even if their saturation times are not the same. The scalar absorption coefficient (α) of the film before photoinduction is about 6.02×10 3 cm -1 at 632.8 nm, that is, it is independent of polarization, but the α after photoinduction depends strongly on the polarization of the probing beam. That is, for a 0.5-µm-thick-film induced for 25 s by a laser with a power of 5.48 mW/cm 2 , the difference of two polarization absorption coefficients ( Δ α= α ⊥ -α ∥ ) for the scalar α is estimated to be about 13.8%, which corresponds to D ∼4.2%. The photoinduced birefringence also depends strongly on the polarization states of the inducing beam. For example, for 0.9-µm-thick As–Ge–Se–S film the saturation values of Δ n are about 0.69×10 -2 , 0.81×10 -2 , and 1.33×10 -2 for the circularly, elliptically, and linearly polarized beams, respectively. In particular, the saturation values of birefringence of the film are not constant for an inducing history but vary significantly.