We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

/pdf/science-and-technology-roadmap-for-graphene-related-two-4q9m7czlkc.pdf

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Magnetocaloric effect: From materials research to refrigeration devices

Over the last decade there have been spectacular developments in ultrafast laser technology, due to the introduction of solid state active materials and of new mode-locking and amplification techniques. These advances, together with the discovery of new nonlinear optical crystals, have fostered the introduction of ultrafast optical parametric amplifiers as a practical source of femtosecond pulses tunable across the visible and infrared spectral ranges. This article summarizes the recent progress in the development of ultrafast optical parametric amplifiers, giving the basic design principles for different frequency ranges and in addition presenting some advanced designs for the generation of ultrabroadband, few-optical-cycle pulses. Finally, we also briefly discuss the possibility of applying parametric amplification schemes to large-scale, petawatt-level systems.

Ultrafast optical parametric amplifiers

POWERFUL, tunable ultraviolet laser sources, required for many spectroscopic applications, rely on the frequency-doubling of lasers in the visible range. Such second-harmonic generation (SHG) depends on the development of nonlinear optical (NLO) materials with high SHG coefficients, a wide transparent region in the ultraviolet, and moderate birefringence. Few such materials are available; those most widely used at present are the inorganic crystals β-BaB2O4 (BBO)1 and LiB3O5 (LBO)2. These crystals are effective for SHG only down to wavelengths of 205 nm (ref. 3), because of a limited ultraviolet-transparent range in the former case and birefringence problems in the latter. We have developed previously4 a new inorganic NLO crystal, KBe2BO3F2 (KBBF), which avoids both of these problems to a large degree. But it is hard to grow large crystals of KBBF because of weak binding between its layered structural units. We have now developed an improved material by rational design: Sr2Be2B2O7 (SBBO), which shares (and in fact slightly improves on) all of the favourable NLO properties of KBBF and is easy to grow as large (so far up to 7 × 7 × 3 mm) crystals of high optical quality. The large SHG coefficients and wide range of ultraviolet transparency make this material a promising candidate for frequency doubling into the ultraviolet.

Design and synthesis of an ultraviolet-transparent nonlinear optical crystal Sr 2 Be 2 B 2 O 7

Nonlinear Optical Crystals: A Complete Survey

The boron–oxygen compound LiB3O5 is recognized as a new nonlinear-optical crystal. This follows theoretical calculations of the second-harmonic generation (SHG) coefficients using the anionic group theory and the complete neglect of differential overlap approximation to obtain the localized wave functions of component groups. An optically perfect single crystal with space group Pna21, grown at the Fujian Institute of Research on the Structure of Matter by the high-temperature flux method, is found to be transparent from 160 nm to 2.6 μm. It has a SHG coefficient comparable with that of β-BaB2O4 as well as two other outstanding advantages: a high damage threshold of 25 GW/cm2 (at 1.064 μm, 0.1 nsec) and a wide acceptance angle of 25 mrad for θ ≠ 90° and 95 mrad for θ = 90° with a 6-mm-long crystal.

New nonlinear-optical crystal: LiB 3 O 5

The nonlinear optical coefficients of lithium triborate LiB3O5 (LBO) have been determined by the method of Maker fringes at λ=1.079 μm. It is found that these coefficients relative to d36 for potassium dihydrogen phosphate are d31=∓2.51 (l±0.09), d32=±2.69 (l±0.12), d33=±0.15 (l±0.10), d15=∓2.30 (l±0.22), and d24=±2.52 (l±0.20). The phase‐matching conditions, effective second‐harmonic generation (SHG) coefficients, walk‐off angles, and acceptance angles for SHG at λ=1.079 μm are also investigated. The figures of merit of LBO in different cases are then compared with those of potassium dihydrogen phosphate (KDP), β‐barium metaborate (BBO), and potassium titanyl phosphate (KTP) crystals. All these figures combined with the damage thresholds of the crystals show that an LBO crystal may operate better than KDP and BBO crystals for frequency conversions of a tightly focused Nd:YAlO3 (YAP) or Nd:Y3Al5O12 (YAG) laser and also a dye laser.

The nonlinear optical characteristics of a LiB3O5 crystal

As another new high quality nonlinear optical (NLO) crystal of the borate series, lithium triborate LBO has been characterized in our Fujian Institute. This follows theoretical calculations of the second harmonic generation (SHG) coefficients on the basis of the anionic group theory (which has been generalized into a general NLO active group theory) with the GNDO approximation. This leads to localized wave functions for the component active anionic group (B3O7)5− and the resultant anionic group (B3O5)−.

Mew nonlinear optical crystal LiB3O5

In this paper, we report the effects of partial substitution of Mn for Cr on the structural, magnetic, and electrical/thermal transport properties of Mn+1AXn phase compounds Cr2−xMnxGaC (0 ≤ x ≤ 1). As a result, the unit cell volume and the thermal conductivity decrease while the resistivity increases with increasing x. Interestingly, the magnetism of Cr2−xMnxGaC changes from the nonmagnetic Cr2GaC (x = 0) to the ferrimagnetic CrMnGaC (x = 1). In order to shed light on the discrepancy observed between Hall coefficient and Seebeck coefficient of Cr2GaC, the electrical conductivity, Hall coefficient, and magnetoresistance are analyzed within a two-band model. Furthermore, an upturn is observed in low-temperature specific heat of Cr2−xMnxGaC, which may be related with the magnetic Mn dopant.

S. Lin

Papers

New nonlinear-optical crystal: LiB 3 O 5

The nonlinear optical characteristics of a LiB3O5 crystal

Mew nonlinear optical crystal LiB3O5

Magnetic and electrical/thermal transport properties of Mn-doped Mn+1AXn phase compounds Cr2-xMnxGaC (0 《 x 《 1)

Tunable temperature coefficient of resistivity in C- and Co-doped CuNMn3