Stable, Surfactant‐Free Graphene–Styrene Methylmethacrylate Composite for Ultrafast Lasers

Abstract

the global range of applications of ultrafast lasers (e.g., manufacturing, biomedical research, telecommunications, spectroscopy, etc.) requires SAs to show thermal and environmental stability (i.e., moisture absorption ≤1% by weight in high, ≥80%, humidity environment and glass transition temperature ≥120 °C, for polymers). [ 11 ] Carbon nanotubes (CNTs), [ 2,12,13 ] graphene [13][14][15] and recently, other 2D materials such as semiconducting transition metal dichalcogenides (MoS 2 , [ 16,17 ] WS 2 , [ 18 ] MoSe 2 [ 19 ] ) and black phosphorus [ 20,21 ] have emerged as promising SAs for ultrafast lasers. [ 2,[22][23][24] In CNTs, broadband operation is achieved by using a distribution of tube diameters, [ 2,22 ] while this is an intrinsic property of graphene. [ 25 ] This, along with the ultrafast recovery time, [ 26 ] low saturation fl uence, [ 15,27 ] and ease of fabrication [ 28 ] and integration, [ 29 ] makes graphene an excellent broadband SA. [ 25 ] Consequently, modelocked lasers using graphene SAs (GSAs) have been demonstrated from ≈800 nm [ 30 ] to ≈970 nm, [ 31 ] ≈1 µm, [ 32 ] ≈1.5 µm, [ 27 ] and ≈2 µm [ 33 ] up to ≈2.4 µm. [ 34 ] Polymeric materials are the ideal solution to integrate GSAs into fi ber lasers. [ 1,35 ] They are easily processed by methods such as embossing, stamping, sawing, and wet or dry etching, and generally have a low-cost room-temperature fabrication process. [ 13,36 ] Liquid phase exfoliation (LPE) of graphite crystals in a surfactant-stabilized aqueous solution [37][38][39] and organic solvents [ 38,40,41 ] can be used to produce graphene. The LPE yield can be defi ned in different ways. [ 29 ] The yield by weight, Y M [%], is defi ned as the ratio between the weight of dispersed graphitic material and that of the starting graphite fl akes. References [ 38,41,42 ] reported surfactant-free dispersions of graphene in organic solvents, e.g., N -methylpyrrolidone (NMP), N -dimethylformamide (DMF), and ortho -dichlorobenzene ( o -DCB). Graphene from LPE is ideal to produce polymer composites as it can be mixed/blended in liquid or dry form with a host polymer matrix. [ 13,38 ] Polymers for composites used in fi ber lasers for ultrashort pulse generation have to be transparent at the device-operation wavelength, be mechanically fl exible, thermally, and chemically stable as well as being resistant to moisture (e.g., hydrophobic) [ 13,35 ] as moisture-induced hygroscopic swelling in polymers can cause internal stress in the polymeric matrix. [ 43 ] Various polymers, such as polyvinylacetate (PVAc), [ 44 ] polyvinylalcohol (PVA), [ 13 ] polymethylmetacrylate (PMMA), [ 45 ] polyaniline (PANi), [ 46 ] polycaprolactone (PCL), [ 47 ] polyurethane (PU), [ 48 ] polystyrene (PS), [ 49 ] polylactide (PLA), [ 50 ] polyethylene Graphene-polymer composites play an increasing role in photonic and optoelectronic applications, from ultrafast pulse generation to solar cells. The fabrication of an optical quality surfactant-free graphene-styrene methyl methacrylate composite, stable to large humidit...

Terahertz saturable absorbers from liquid phase exfoliation of graphite

“…for 1 h and the top 70% is collected for further characterization. Rheological measurements (viscosity, surface tension, density) give η GW ∼1.3 mPa s, γ GW ∼48 mN m −1 , ρ GW ∼0.8 g cm −3 ; η GEth ∼2.2 mPa s, γ GEth ∼30.7 mN m −1 , ρ GEth ∼0.98 g cm −3 , consistent with previous reports333435363738. Optical absorption spectroscopy is used to estimate the flakes concentration183132 via the Beer–Lambert law, which correlates the absorbance A = αcl , with the beam path length l [m], the concentration c [g l −1 ] and the absorption coefficient α [l g −1  m −1 ].…”

“…Graphene from LPE can be mixed or combined in dry or liquid form with a host polymer matrix, and can be used to produce both SAs1833 and printable inks3435. Inkjet printing then allows for the deposition of films at low temperatures (<60 °C), with 1200 dpi resolution36.…”

Solution-processed two-dimensional materials for ultrafast fiber lasers (invited)

“…The most popular exfoliation method used to fabricate SAs is ultrasonication, in which ultrasound waves are employed to disrupt the weak inter-layer van der Waals forces within the 2D crystal ( Figure 1A, B). Ultrasonication has proved effective for most 2DM-based SAs, including graphene [36,41,[62][63][64][65][66][67]133], TIs [16, 59, 89, 91, 105, 107-111, 114, 136-138], TMDs [19, 39, 60, 74, 83-89, 91, 92, 96, 97, 99-104, 135, 139-142], and BP [42,[116][117][118][119][120][121][122][123][124][125][126][127][128][129][130][143][144][145]. Its popularity arises from the ease of use, low cost, and immediate availability across most laboratories [55,146,147].…”

Fused Silica with Embedded 2D‐Like Ag Nanoparticle Monolayer: Tunable Saturable Absorbers by Interparticle Spacing Manipulation

“…In particular, rapid developments in multi‐gigahertz (GHz) mode‐locked lasers are stimulated by advances in the novel saturable absorber (SA) materials with superior nonlinear optical (NLO) response . Based on large optical nonlinearities and ultrafast dynamic responses, semiconductor saturable absorber mirrors (SESAMs) and 2D materials (such as graphene, black phosphorus, and transition metal dichalcogenides [TMDCs]) have become excellent SAs for ultrafast laser generation . Nonetheless, traditional commercially available SESAMs usually have the drawbacks of high‐cost, complex fabrication process, and limited NLO response band .…”