Nonlinear optical responses of α-Fe2O3 nanosheets and application as a saturable absorber in the wide near-infrared region

In the present work, we report a strategy to synthesize alpha-Fe2O3 nanoflakes as a nonlinear optical (NLO) material for the optical pulse generation in the near-infrared (NIR) band. With the excitation wavelength of 1 mu m, the effective nonlinear absorption coefficients beta(eff )was -0.501 cm/GW and the nonlinear refractive index n(2) was 9.33 x cm(2)/GW. While at 1.34 mu m, beta(eff )was -0.713 cm/GW and n(2) was 5.01 x 10(-4) cm(2)/GW. The two-photon absorption cross sections at 1 and 1.34 mu m were as high as 9.6 x 10(5) and 5.7 x 10(5) GM, respectively, indicating that the hematite nanosheets could be used as the nonlinear optical devices. The third-order NLO susceptibilities were 6.3 x 10(-11) and 3.75 x 10(-11) esu at 1 and 1.3 mu m, respectively. Using the ultrafast spectroscopy, the excited state lifetime was similar to 2.62 ps, suitable for the (ultra)short pulse generation. Based on the marvelous nonlinear absorption properties of the alpha-Fe2O3 nanoflakes saturable absorber, passively Q-switched Nd:GdVO4 lasers at F-4(3/)2 -> I-2(11/2) and F-4(3/2) -> I-2(13/2) lasing transitions were demonstrated, producing the shortest pulse duration of 135 ns. The experimental results confirmed that alpha-Fe2O3 nanoflakes were an excellent candidate for the short NIR pulse generation in a broad band.

Automated summary

This study introduces a strategy to synthesize alpha-Fe2O3 nanoflakes as a nonlinear optical material for optical pulse generation in the near-infrared band. The experimental results demonstrate the excellent nonlinear absorption properties of alpha-Fe2O3 nanoflakes, making them a promising candidate for short NIR pulse generation in a broad band.