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Abstract. Laser photoacoustic spectroscopy (PAS) is a method that utilizes the sensing of the pressure waves that emerge upon the absorption of radiation by absorbing species. The use of the conventional electret microphone as a pressure sensor has already reached its limit, and a new type of microphone -an optical microphone -has been suggested to increase the sensitivity of this method. The movement of a micro-lever or a membrane is sensed via a reflected beam of light, which falls onto a position-sensing detector. The use of one micro-lever as a pressure sensor in the form of a silicon cantilever has already enhanced the sensitivity of laser PAS.Herein, we test two types of home-made sensing elements -four coupled silicon micro-levers and a multilayer graphene membrane -which have the potential to enhance this sensitivity further. Graphene sheets possess outstanding electromechanical properties and demonstrate impressive sensitivity as mass detectors. Their mechanical properties make them suitable for use as micro-/nano-levers or membranes, which could function as extremely sensitive pressure sensors.Graphene sheets were prepared from multilayer graphene through the micromechanical cleavage of basal plane highly ordered pyrolytic graphite. Multilayer graphene sheets (thickness ∼ 10 2 nm) were then mounted on an additional glass window in a cuvette for PAS. The movements of the sheets induced by acoustic waves were measured using an He-Ne laser beam reflected from the sheets onto a quadrant detector. A discretely tunable CO 2 laser was used as the source of radiation energy for the laser PAS experiments. Sensitivity testing of the investigated sensing elements was performed with the aid of concentration standards and a mixing arrangement in a flow regime. The combination of sensitive microphones and micromechanical/nanomechanical elements with laser techniques offers a method for the study and development of new, reliable and highly sensitive chemical sensing systems. To our knowledge, we have produced the first demonstration of the feasibility of using four coupled silicon micro-levers and graphene membranes in an optical microphone for PAS. Although the sensitivity thus far remains inferior to that of the commercial electret microphone (with an S/N ratio that is 5 times lower), further improvement is expected to be achieved by adjusting the micro-levers and membrane elements, the photoacoustic system and the position detector.

The applicability of cantilever-enhanced photoacoustic spectroscopy (CEPAS), which exploits the unique properties of a micromechanical lever sensor (cantilever) in combination with tunable quantum cascade lasers (QCLs), is evaluated for the monitoring of several species produced by biomass burning. The detection limits of the selected molecules (HCOOH, CH3CN, CH3OH, CH3COCH3, CO2, and N2O) for a commercial CEPAS unit (GASERA) used together with QCLs were estimated under laboratory conditions. The normalized noise equivalent absorption (NNEA) coefficients for these molecules were determined experimentally, and the theoretical detection limits for the relevant biomass-burning products, accessed in the spectral ranges of available commercial QCLs in the mid-infrared region, were extrapolated using the determined NNEA values and the spectra simulated with the SpectraPlot software.

Abstract. The availability of reliable modeling tools and input data required for the prediction of surface removal rate from the lithium fl uoride targets irradiated by the intense photon beams is essential for many practical aspects. This study is motivated by the practical implementation of soft X-ray (SXR) or extreme ultraviolet (XUV) lasers for the pulsed ablation and thin fi lm deposition. Specifi cally, it is focused on quantitative description of XUV laser-induced desorption/ablation from lithium fl uoride, which is a reference large band-gap dielectric material with ionic crystalline structure. Computational framework was proposed and employed here for the reconstruction of plume expansion dynamics induced by the irradiation of lithium fl uoride targets. The morphology of experimentally observed desorption/ablation craters were reproduced using idealized representation (two-zone approximation) of the laser fl uence profi le. The calculation of desorption/ablation rate was performed using one-dimensional thermomechanic model (XUV-ABLATOR code) taking into account laser heating and surface evaporation of the lithium fl uoride target occurring on a nanosecond timescale. This step was followed by the application of two-dimensional hydrodynamic solver for description of laser-produced plasma plume expansion dynamics. The calculated plume lengths determined by numerical simulations were compared with a simple adiabatic expansion (blast-wave) model.

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