We describe the benign wet chemical synthesis, characterization, and third-order nonlinear optical properties of hydrogenated fluorographene, namely, of a new 2D counterpart of hydrogenated graphene (graphane). The presence of hydrogen in hydrogenated fluorographene was confirmed using infrared spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis coupled with evolved gas analysis. The nonlinear optical properties of the derivative were investigated in the visible and infrared using picosecond laser excitation and were compared to those of graphene and fluorographene. All samples were found to exhibit important nonlinear optical response, with hydrogenated fluorographene exhibiting the largest response under visible excitation (ca. 1 order of magnitude higher compared to graphene and fluorographene). This is among the highest recorded effects ever observed for any graphene-based materials, including graphene oxide presented elsewhere. The results reveal the importance of the nature of the functional group and the degree of functionalization (i.e., fluorination and hydrogenation) on the nonlinear optical properties of graphenes. It is likely that highly polarized donor-π electron-acceptor regions within a layer result in such large optical nonlinearities.

An experimental study of laser-produced plasmas is performed by irradiating a planar tin target by laser pulses, of 4.8 ns duration, produced from a KTP-based 2-µm-wavelength master oscillator power amplifier. Comparative spectroscopic investigations are performed for plasmas driven by 1-µm- and 2-µm-wavelength pulsed lasers, over a wide range of laser intensities spanning 0.5 − 5 × 1011 W/cm 2. Similar extreme ultraviolet (EUV) spectra in the 5.5–25.5 nm wavelength range and underlying plasma ionicities are obtained when the intensity ratio is kept fixed at I1µm/I2µm = 2.4(7). Crucially, the conversion efficiency (CE) of 2-µm-laser energy into radiation within a 2% bandwidth centered at 13.5 nm relevant for industrial applications is found to be a factor of two larger, at a 60 degree observation angle, than in the case of the denser 1-µm-laser-driven plasma. Our findings regarding the scaling of the optimum laser intensity for efficient EUV generation and CE with drive laser wavelength are extended to other laser wavelengths using available literature data.

Experimental spectroscopic studies are presented, in a 5.5-25.5 nm extreme-ultraviolet (EUV) wavelength range, of the light emitted from plasma produced by the irradiation of tin microdroplets by 5-ns-pulsed, 2µm-wavelength laser light. Emission spectra are compared to those obtained from plasma driven by 1-µmwavelength Nd:YAG laser light over a range of laser intensities spanning approximately 0.3 − 5 × 10 11 W cm −2 , under otherwise identical conditions. Over this range of drive laser intensities, we find that similar spectra and underlying plasma charge state distributions are obtained when keeping the ratio of 1-µm to 2-µm laser intensities fixed at a value of 2.1(6), which is in good agreement with RALEF-2D radiation-hydrodynamic simulations. Our experimental findings, supported by the simulations, indicate an approximately inversely proportional scaling ∼ λ −1 of the relevant plasma electron density, and of the aforementioned required drive laser intensities, with drive laser wavelength λ . This scaling also extends to the optical depth that is captured in the observed changes in spectra over a range of droplet diameters spanning 16-51 µm at a constant laser intensity that maximizes the emission in a 2% bandwidth around 13.5 nm relative to the total spectral energy, the bandwidth relevant for EUV lithography. The significant improvement of the spectral performance of the 2-µm-vs 1-µm driven plasma provides strong motivation for the development of high-power, high-energy nearinfrared lasers to enable the development of more efficient and powerful sources of EUV light.