Black phosphorus as broadband saturable absorber for pulsed lasers from 1μm to 2.7μm wavelength

Abstract

It attracts wide interest to seek universe saturable absorber covering wavelengths from near infrared to midinfrared band. Multilayer black phosphorus, with variable direct bandgap (0.3-2 eV) depending on the layer number, becomes a good alternative as a universe saturable absorber for pulsed lasers. In this contribution, we first experimentally demonstrated broadband saturable absorption of multilayer black phosphorus from 1 μm to 2.7 μm wavelength. With the as-fabricated black phosphorus nanoflakes as saturable absorber, stable Qswitching operation of bulk lasers at 1.03 μm, 1.93 μm, 2.72 μm were realized, respectively. In contrast with large-bandgap semiconducting transition metal dichalcogenides, such as MoS 2 , MoSe 2 , multilayer black phosphorus shows particular advantage at the long wavelength regime thanks to its narrow direct bandgap.This work will open promising optoelectronic applications of black phosphorus in mid-infrared spectral region and further demonstrate that BP may fill the gap of between zero-bandgap graphene and large-bandgap TMDs.Keywords: multilayer black phosphorus; saturable absorber; mid-infrared pulsed laser. IntroductionBlack phosphorus (BP), a layered allotrope of phosphorus, owns its unique properties. Due to puckered layer or zigzag direction of intralayer atoms, the BP crystal exhibits highly anisotropic mechanical properties [1].Moreover, few-layered BP presents highly anisotropic electric conductance and strain-controlled anisotropic electric mobility [2]. By use of its high carrier mobility, few-layer BP has been manufactured into fast fieldeffect transistors (FETs) and opens its electronic applications [3][4]. Similar to MoS 2 , BP also possesses thickness-depended energy bandgap with 1.5-2.0 eV for single layer [5][6][7], 0.59 eV for five layers [8] and 0.3-0.33 eV for bulk sample [1,3]. However, MoS 2 shows a transition from direct bandgap to indirect bandgap once it becomes multilayer while BPs always show direct bandgap property [5]. Such difference would endow multilayer BPs with intrinsically stronger light-matter interaction than multilayer MoS 2 . This might lead to

Black Phosphorus Q-Switched Large-Mode-Area Tm-Doped Fiber Laser

“…More importantly, BP has a thickness-dependent direct energy bandgap from 0.3 eV (bulk) to 2.0 eV (single layer) [15], filling up the interval between the zero gap of graphene and large gap of TMDCs, which is of great importance to the optical applications. Up to now, the broadband BP saturable absorbers have been widely applied to pulsed lasers in a wide spectral range from visible to mid-infrared [16][17][18][19][20][21][22][23][24][25]. Specifically, in 2 m Q-switched fiber lasers, Wang et al reported a passively Q-switched Tmdoped fiber laser using a BP deposited microfiber, delivering the maximum pulse energy of 154 nJ [26]; Jiang et al deposited the BP powders onto a side-polished fiber and achieved Q-switched operation with the maximum pulse energy of 276 nJ [27].…”

Watt-level high-power passively Q-switched laser based on a black phosphorus solution saturable absorber

“…In addition, BP is a highmobility semiconductor with a direct bandgap sensitivity depending on the number of layers from 0.3 (bulk) to 2.0 eV (single layer) that exactly fill the gap between the zero bandgap of graphene and the wide bandgap (1.0-2.0 eV) of TMDs [25] . The narrower bandgap of BP makes itself act as the SA, which has been used in a broader wavelength operation range of 4-0.8 μm [26,27] . In addition, like graphene, BP SA owns the same excellent nonlinear optical response and easy fabrication process [13,23] .…”

“…In addition, like graphene, BP SA owns the same excellent nonlinear optical response and easy fabrication process [13,23] . Q-switching or mode locking in SSLs using graphenelike absorbers [9,15,16,18,20,21,26,27,[29][30][31][32][33][34][35] are listed in Table 1. These absorbers are made by growing nanomaterials by chemical vapor deposition and transferring themon a mirror or depositing them on the quartz substrate by the spin-coating method.…”

“…We observe that three peaks appear at 357. [23,[25][26][27] . Figure 1(d) shows the nonlinear transmission curve of the BP solution SA, which is measured by a 150 fs titanium gem laser at 800 nm with a Figure 2 shows the schematic of a passively QS Nd:YVO 4 laser with an 18 cm long V-type cavity (L 1 ¼ 2 cm, L 2 ¼ 10 cm, L 3 ¼ 6 cm).…”

“…% Nd 3þ is employed as the gain media, and two light-passing faces of the crystal are coated for 808 nm and 1064 nm antireflection (AR) film. In order to improve the thermal diffusion, the crystal is wrapped with indium foil and mounted in a water-cooled copper block maintained at 21°C by a cool-water machine [27,35] . An 808 nm fiber-coupled diode laser with a core diameter of 200 μm and a numerical aperture of 0.22 is used as the pump source, of which the maximum output power is 30 W. Through a 1∶2 optical focusing system, the pump laser is focused on the gain crystal with a diameter of 400 μm.…”