By using a repetition rate of 1 Hz, induced transparency (saturable absorption
) is obtained, while the increase in the repetition rate to 10Hz notably produces the signature of a multiphotonic absorption (induced absorption) process in the sample.
Compared with traditional saturable absorbers, such as semiconductor saturable absorber mirrors (SESAMs) [10,11], single-walled carbon nanotubes (SWCNTs) , graphene , transitional metal dichalcogenides [14,15], black phosphorus [16,17], topological insulator saturable absorber possesses many good qualities, such as low saturable absorption
threshold, large modulation depth [18, 19], short recovery time [20, 21], and wavelength independent saturable absorption
Runcorn et al., "Wideband saturable absorption
in few-layer molybdenum diselenide (Mo[Se.sub.2]) for Q-switching Yb-, Er- and Tm-doped fiber lasers," Optics Express, vol.
This indicates the reverse saturable absorption
(RSA) type of process.
In particular, a property called saturable absorption
changes drastically at high laser intensities.
Monolithic cavity devices with gain, gain modulation and saturable absorption
functions integrated on a single semiconductor chip are easy-to-use.
If [[chi].sup.(3).sub.I] < 0, then the z-scan will produce a peak near the focus, indicating induced transparency (due to saturable absorption
, for example).
Figure 2(a) shows the typical open-aperture curve of the Mo[Te.sub.2] sample, which manifests that the material can exhibit nonlinear saturable absorption
If the ESA cross section is larger than that of the ground state, [[sigma].sub.ex] > [[sigma].sub.g], then the absorption process is referred to as reverse saturable absorption
Since the Nd:glass (the first generation of SA) was successfully used for pulse generation in 1966 , a wide variety of SAs have been intensively developed, such as Semiconductor Saturable Absorption
Mirrors (SESAMs) [8, 9], Carbon Nanotubes (CNTs) , graphene [14-18], Topological Insulator (TI) [19, 20], and Transition Metal Dichalcogenides (TMDs) [21-24].
The absorption may be clue to two photon absorption (TPA), excited state absorption (ESA), reverse saturable absorption
The experiment results reveal the saturable absorption
behaviors of the TI: [Bi.sub.2][Te.sub.3], with normalized modulation depth of 47% and saturable intensity of 32 [micro]W/[cm.sup.2].