Thickness dependence of a giant nonlinear saturable absorption response in GeSb₄Te₇ thin films

Nonlinear optical absorption (NOA) materials with large saturable absorption response and high damage threshold are useful for a variety of applications such as ultrafast nonlinear optical devices and laser mode lockers. In this study, a suite of GeSb₄Te₇ thin films with different thicknesses were prepared, and the surface morphology, structure and linear optical absorption of these films were investigated in detail. Through an open aperture Z-scan technique with femtosecond pulses at 800 nm wavelength, it is found that effective NOA coefficient as high as −93 009 cm GW⁻¹ can be achieved in GeSb₄Te₇ thin films. Besides, GeSb₄Te₇ thin films exhibit a giant and ultrafast third-order nonlinear optical saturable absorption response due to significant band filling effect. Especially, NOA response, coefficient and damage threshold can be well controlled by adjusting the film thickness. Both stability and efficiency can be acquired by thermal treatment. (paper)