A new ion acceleration method, namely, phase-stable acceleration, using circularly-polarized laser pulses is proposed. When the initial target density n(0) and thickness D satisfy a(L) approximately (n(0)/n(c))D/lambda(L) and D>l(s) with a(L), lambda(L), l(s), and n(c) the normalized laser amplitude, the laser wavelength in vacuum, the plasma skin depth, and the critical density of the incident laser pulse, respectively, a quasiequilibrium for the electrons is established by the light pressure and the space charge electrostatic field at the interacting front of the laser pulse. The ions within the skin depth of the laser pulse are synchronously accelerated and bunched by the electrostatic field, and thereby a high-intensity monoenergetic proton beam can be generated. The proton dynamics is investigated analytically and the results are verified by one- and two-dimensional particle-in-cell simulations.

It has been a great challenge to achieve the direct light manipulation of matter on a bulk scale. In this work the direct light propulsion of matter is observed on a macroscopic scale using a bulk graphene-based material. The unique structure and properties of graphene, and the novel morphology of the bulk three-dimensional linked graphene material make it capable not only of absorbing light at various wavelengths but also of emitting energetic electrons efficiently enough to drive the bulk material, following Newtonian mechanics. Thus, the unique photonic and electronic properties of individual graphene sheets are manifested in the response of the bulk state. These results offer an exciting opportunity to bring about bulkscale light manipulation with the potential to realize long-sought applications in areas such as the solar sail and space transportation driven directly by sunlight.U sing beams of light, scientists have been able to trap 1 , move 2 , levitate 3 and even pull 4 small objects (such as atoms and molecules, living cells and viruses, and micro/nanoscopic particles) on the microscopic scale, as well as nano/micrometre-sized graphene sheets 5-7 on a small spatial scale, typically on the order of hundreds of micrometres 8 . There have also been reports of efforts to enlarge the optical manipulation distance by harnessing strong thermal forces 9 , and also the robust manipulation of airborne micro-objects photophoretically with a bottle beam 10 . Furthermore, the rotation and motion of a millimetre-sized graphite disk by photoirradiation has been realized with the graphite levitated magnetically 11 . If these optical operations were to be achieved with large objects on a macroscopic spatial scale, significant applications such as the long-sought direct optical manipulation of macroscale objects (including the proposed solar sail and space transportation via laser or beam-powered propulsion) could be realized. To acquire the required energy and momentum for propulsion, two main mechanisms have been proposed: the use of a laser to superheat a propellant (or air), which then provides propulsion in the same manner as a conventional rocket 4,12,13 , or obtaining propulsion directly from light pressure (radiation pressure) acting on a light sail structure (as with the IKAROS spacecraft) 14,15 .It has been a great challenge to realize the intrinsic properties of single-layer graphene in the bulk state, because stacking of the graphene sheets diminishes most of its properties (electronic, photonic and even mechanical). In this Article, we show that if graphene sheets are assembled in the proper manner into the bulk state, the resulting bulk material not only can retain the intrinsic properties of the individual graphene sheets, but also allows their manifestation on a macroscopic scale. Here, we demonstrate the directly lightinduced macroscopic propulsion and rotation of a bulk graphene sponge material with dimensions on the scale of a centimetre and milligram weight. The mechanism behind this novel phenomenon ...

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Graphene, a two-dimensional carbon atom sheet, has attracted tremendous attention and research interest because of its exceptional physical properties. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. The main focus so far has been on fundamental physics and electronic devices. However, because the linear dispersion of the Dirac electrons enables ultrawideband tunability, we believe its true potential lies in photonics and optoelectronics. In this review, we introduce recent advances in the nonlinear optical properties of graphene-based materials. The rise of graphene in nonlinear optics is shown by several recent results, ranging from saturable absorbers and the four-wave mixing effect to giant two-photon absorption, reverse saturable absorption and optical limiting. The relevant forms of the graphene-based materials include pure graphene, graphene oxide and graphene hybrids.

Many interesting phenomena and unique properties given by reduced dimensions make 2D materials very attractive recently [1,2]. These 2D materials include graphene [3], black phosphorus [4] and TMDs, among which TMDs show promising application in optoelectronic and photonic devices (such as, solar cell, sensor, and photodetector) due to the tunable bandgap, high carrier mobility and large optical absorption [6][7][8][9]. For manipulating the application of these 2D materials, there has been much research on the optical and electronic properties of TMDs [10,11]. These works mainly focused on the classic TMDs with 2H-phase, such as MoS 2 and WSe 2 et al [10,11].Platinum diselenide (PtSe 2 ) is a group-10 TMD with 1T-phase. Many methods are employed to synthesize PtSe 2 , such as direct selenization of Pt film, thermally assisted conversion (TAC) and chemical vapor deposition (CVD) [12][13][14]. The strong interlayer interaction and intrinsic quantum confinement effect make the bandgap of PtSe 2 greatly tunable, leading to a type-II Dirac semimetal-to-semiconductor transition when going from bulk to few-layer form and exhibiting a biggest bandgap of ~1.2 eV for monolayer (ML) PtSe 2 (from theoretical prediction) [14,15]. Furthermore, the bandgap of PtSe 2 can be modulated by applying different types of strain [16]. Among the studied TMDs, the carrier mobility of ML PtSe 2 is the highest and comparable to that of black phosphorus [17]. In addition, the Raman spectrum [18] and absorption spectrum [19] of PtSe 2 show strong dependence on the thickness. The interesting properties render it be a top-priority candidate for functional material in transistors, photodetectors, optical sensors, chemiresistors and photocatalysts [12,14,15]. Manipulating the application of PtSe 2 in optoelectronic and photonic fields requires an accurate description of their optical response. Thus, it is necessary to know the optical constants (i.e. refractive index n and extinction coefficient k) of PtSe 2 and how the values vary with the thickness. Moreover, the k spectrum is a macroscopic

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Based on the polarization-sensitive absorption of graphene under conditions of total internal reflection, a novel optical sensor combining graphene and a microfluidic structure was constructed to achieve the sensitive real-time monitoring of refractive indexes. The atomic thickness and strong broadband absorption of graphene cause it to exhibit very different reflectivity for transverse electric and transverse magnetic modes in the context of a total internal reflection structure, which is sensitive to the media in contact with the graphene. A graphene refractive index sensor can quickly and sensitively monitor changes in the local refractive index with a fast response time and broad dynamic range. These results indicate that graphene, used in a simple and efficient total internal reflection structure and combined with microfluidic techniques, is an ideal material for fabricating refractive index sensors and biosensor devices, which are in high demand.