Optical properties and potential applications of ɛ-GaSe at terahertz frequencies

Abstract

Ordinary and extraordinary refractive indices of an ε-GaSe crystal at terahertz (THz) frequencies are experimentally determined in this study. Fitting experimental data by THz time-domain spectroscopy (THz-TDS) and a Fourier transform infrared spectrometer (FTIR), we proposed revised complex dielectric functions and Sellmeier equations of GaSe for both ordinary and extraordinary waves from 0.2 to 100 THz. Phonon vibrational modes and overtones in the THz frequency range are examined in detail. The high magnitude of the figure of merit (FOMϳ 10 3 at 1 THz), the large birefringence (⌬n ϳ 0.76 at 1 THz). and the low absorption coefficient (␣ ϳ 0.2 cm −1 at 1 THz) of GaSe are also identified. Potential applications to practical photonic devices such as phase shifters at THz frequencies are proposed.

Doped GaSe crystals for laser frequency conversion

“…With further study, the extraordinary refractive index for GaSe was found to be significantly lower, and the birefringence was found to be larger, than those values calculated using data from (Figure 11). 3,77,78 The dispersion equations for the ordinary refractive index referred to in papers 3,77,78 have a common origin in Palik's paper 79 ,which resulted in the similarity of the calculated curves (Figure 11a). …”

“…In particular, a pair of Vodopyanov's dispersion equations 77 Doped GaSe for frequency conversion J Guo et al 6 dispersion equations for THz range have been proposed by Chen et al 3 The ordinary and extraordinary refractive indices for solid solutions GaSe 12x S x decrease in proportion to the mixing ratio magnitudes, from GaSe to GaS. Thus, the S-content in GaSe can be estimated from the refractive indices.…”

“…The performance potential of GaSe, which belongs to the point group symmetry 6m2, can be attributed to its extreme physical properties. GaSe has a broadband transparency window over the range of 0.62-20 mm for non-polarized light continues at wavelengths o50 mm 2,3 . Other attractive physical properties of GaSe are its prodigious birefringence B 5 0.375 at l 5 10.6 mm and 0.79 at terahertz (THz) range 4 , and very high second-order nonlinear susceptibility d 22 5 54 pm V 21 at 10 mm 5 and 24.3 pm/V in the THz band 6 .…”

Dispersion properties of sulfur doped gallium selenide crystals studied by THz TDS

“…ε-polytype gallium selenide (hereinafter GaSe) promises efficient laser down-conversion almost over the entire THz range [2,3], except for the phonon absorption gap around 44 μm [2,4]. Owing to the large birefringence of GaSe (0.35 at 10 μm [5] and up to 0.79 [6] at 1 THz), phase matching can be achieved in multiple geometries: the common forward k 1 − k 2 = k 3 type II (oe → e) [2,3,[7][8][9][10][11]; (eo → e) [2] and (oe → o); [12], type I (ee → o) [10,13]; (oo → e) [14]; the original (ee → e) [15,16]; and backward type II (oe → e) [17].…”

Growth and optical parameters of GaSe:Te crystals

“…Gallium selenide (GaSe) is one of the most promising materials for conversion of optical frequencies in the infrared and terahertz spectral regions [1][2][3][4]. In comparison with other known noncentrosymmetrical chalcogenide crystals, GaSe possesses a high effective nonlinear coefficient and significant birefringence, which opens wide possibilities for phase matching between the interacting light waves [1, 4, and 5].…”