Spectroscopy experiments of the inelastic scattering of laser pulses in an aqueous suspension of silicon dioxide (SiO2) nanoparticles at room temperature have revealed for the first time that the centroid of the OH Raman scattering band is shifted to the pump line up to 10 cm–1 and two components of stimulated backward and forward Brillouin scattering with frequency shifts of 7.5 and 14.3 GHz are simultaneously generated. The frequency shift 7.5 GHz corresponds to the Stokes component of Brillouin scattering in water (speed of sound of 1490 m/s), while the 14.3 GHz shift component corresponds to the speed of sound of 2900 m/s; i.e., this component falls within the range of speeds of sound in ice at room temperature. In our opinion, the results of these experiments indicate both the formation of hydrate layers with an ice-like hydrogen bonding structure around SiO2 nanoparticles and a decrease in the volumetric thermal expansion coefficient of the aqueous suspension.

The detailed study of the different signal statistics in laser induced breakdown spectroscopy (LIBS) measurements has been carried out. It was demonstrated that the Nd:YAG laser pulse energy distribution function is not described by the Gaussian distribution function, but can follow the normal distribution if proper lasing conditions (pumping level, Q-switch type, etc.) are chosen. The time gated LIBS signals (atomic lines intensity, plasma background emission, acoustic signal) have been shown to be biased from a Gaussian distribution function. Alternatively, distribution function of the time and spectra integrated plasma emission corresponded to the normal distribution. The normalization procedure did not change the distribution functions for LIBS signals so the generalized extreme value distribution was a better choice. In case of the generalized extreme value distribution for the LIBS signals, the limits of detection should be defined by distribution functions rather than calibration curve and “3-sigma criteria” approach.

When excited by a powerful picosecond pulse of the second harmonic of a YAP:Nd laser, inelastic scattering lines with frequency detunings in the range of 10–130 GHz relative to the laser line were detected in suspensions of morphologically similar AltMV and PVX viruses. This scattering has a threshold nature, and the sets of its spectral lines are different for different virus samples.

The review presents both new theoretical and practical results of the application of modern physical methods and technologies in agriculture. Physical technologies and materials for passive management of the solar spectrum in greenhouses are considered. A review of the instrumentation used for laser remote sensing of agro- and biosystems and modern laser express technologies used for express analysis of the chemical composition of a substance is carried out. Optical methods used in biological and agricultural diagnostics, including methods based on Mueller polarimetry, are described in detail. A separate chapter of the review is devoted to the production and application of nano -sized objects in agriculture and the food industry. The use of numerous plasma technologies in agriculture is considered.

Consideration is given to the stationary mode of electromagnetic field oscillations in a resonator filled with a nanodisperse liquid suspension and excited by an external monochromatic wave. A general case of excitation of field oscillations in a resonator at an arbitrary ratio between the field and thermal energies of nanoparticles is investigated. It is shown that the increase in the field intensity in the resonator is nonlinear due to spatial redistribution of impurity dielectric particles and that the increase in the pump intensity may allow changing the resonator transmission and blocking radiation not associated with light absorption by the particles.

In a series of measurements, a comparison is made of nonlinear scattering in suspensions of porous silicon nanoparticles in ethanol and bidistilled water. Scattering has a threshold character in terms of the concentration of nanoparticles and the energy of the initiating laser. With a small difference in the sizes of nanoparticles, a significant difference in the nature of scattering spectra and optimal concentrations of suspensions is observed.

A set of vibrational eigenmodes of the tobacco mosaic virus is recorded in the frequency range of 4‒50 GHz in experiments on stimulated inelastic scattering of laser light in a liquid suspension of viral nanoparticles. The data obtained in this way is proposed to be used for rapid optical identification of viruses.

— A shift of the frequency of resonances of stimulated low-frequency Raman scattering (SLFRS) of laser radiation in liquid suspensions of viruses with a change in the pump wave intensity has been found for the first time. It is shown that the experimentally observed dependence of the frequency of these resonances in a suspension of tobacco mosaic virus (TMV) on the pump intensity is explained in terms of the scattering mechanism proposed by us previously.

Stimulated low-frequency scattering spectra in a suspension of two morphologically similar viruses, Alternanthera mosaic virus and Potato virus X the frequency range 1–60 GHz, were calculated and successively measured under the same conditions. Differences in the values of the eigen frequencies of the studied viruses were found. These frequencies make it possible to identify viruses and act on them to suppress their activity. The difference in the low-frequency spectra of stimulated scattering of laser radiation, despite the similar morphology of the virions, is due, in our opinion, to the difference in the mechanical properties of the viruses.

Ultracompact (~300 g) fluorescence LIDAR is developed to be installed on a small drone for remote sensing of agricultural fields. The LIDAR is based on a diode laser (405 nm, 150 mW) and a mini spectrometer allows reducing the device sizes and power consumptions for its placing on small aircraft drones. For field testing, the LIDAR was placed on a quadcopter for remote sensing of plants in maize field. Field testes proved the feasibility and perspectives of autonomous LIDAR sensing from drones for early detection and field locations with plants under stress.

Abstract—In a series of experiments aimed at testing the reproducibility of stimulated inelastic scattering spectra in suspensions of tobacco mosaic virus nanoparticles, it is found that “freshly prepared” samples feature identical spectra, including those for different virus concentrations in liquid. Sample preparation was accompanied by control measurements within standard biochemical procedures. Using standard control procedures with these virus suspension samples, no changes were detected. However, further laser experiments revealed that virus suspension storage for three years at a temperature of +4°C led to a noticeable change in the stimulated inelastic light scattering spectrum. Differences in the spectra can be due to substructural changes in the virion, for the detection of which standard methods used in virological studies are inapplicable. It is proposed to use stimulated laser light scattering spectroscopy for diagnosing small changes in virions in the native environment.

The propagation of a linearly polarized transverse sound wave in a semiconductor layer with a certain crystallographic structure with a sufficiently high concentration of conduction electrons is considered. The semiconductor layer is located in a spatially uniform magnetic field directed perpendicular to the plane of incidence of the sound wave and modulated with the sound frequency. The relationship between the plasma subsystem and acoustic oscillations in the layer is achieved due to the internal piezoelectric field. It is shown that propagation of a sound beam under these conditions is accompanied by a counterpropagating sound wave with a conjugated wave front. The conversion coefficient of direct and phase-conjugated waves is found.

For the first time, stimulated dynamic scattering of a light wave in a liquid nanodispersed medium is observed, which is caused by phase modulation of the dipole moment of the suspension nanoparticles subjected to acoustically induced vibrations in the electromagnetic field. Experiments have been carried out in an aqueous suspension of amorphous silicon dioxide SiO2 nanospheres ≈100 and ≈350 nm in diameter under stimulated scattering excited by the second-harmonic radiation of the pulsed single-mode Nd3+:YAG laser. In addition to the first Stokes component of the stimulated Brillouin scattering with the frequency shift Ω typical of a solvent, a scattering line with the frequency shift ≈2Ω is observed in full agreement with the theory developed in the work.

A lidar backscattering signal from an opaque target object, passed through a 9-m water layer with scattering meshes on the laser beam path, has been detected (for the first time, to the best of our knowledge) when sensing by pulses with eye-safe radiation energy density ( 1 μJ/cm2). The new principle of laser sensing makes it possible to measure the position of meshes on the lidar path, in contrast to conventional laser rangefinders, which measure the distance to only the first target. The lidar has been developed based on a pulsed diode-pumped Nd3+:YAG laser (532 nm, 3 ns, 2 µJ/pulse, pulse repetition rate 4 kHz) and gated single-photon avalanche photodiode (SPAD) with a gain up to 106, serving as a detector. The large gain of the detector and suppression of its noise by gating ensured a signal-to-noise ratio of ≈35 for the target signal, which provides an estimate of underwater sensing range up to 30 m, according to the 3σ detection criterion. Compact lidars based on diode lasers ( 1 µJ/pulse) with a radiation wavelength ( 450 nm) in the spectral range of minimum losses in water and the increase in the safety of manned and unmanned underwater vehicles at early detection of nets (invisible for sonars) by a lidar are discussed.

A physical mechanism of stimulated light scattering on nanoscale objects in a water suspension is pro-posed. The proposed mechanism is based on the dipole interaction between the light wave and the inevitable uncompensated electrical charge on a nanoscale object (e.g., a virus or nanoparticle) in a water environment. Experimental data on the tobacco mosaic virus are presented to support the proposed physical mechanism. It is demonstrated that stimulated amplification spectral line frequencies observed experimentally are well explained by the proposed mechanism. In particular, the absence of lower-frequency lines and the shifting of generation lines when the pH changes are due to ion friction in the ionic solution environment. The selection rules observed experimentally also confirm the dipole interaction type. It is shown that microwave radiation on the nanoscale object acoustic vibrations frequency should appear under such scattering conditions. We demonstrate that such conditions also allow for local selective heating of nanoscale objects from dozens to hundreds of degrees Celsius. This effect is controlled by the optical irradiation parameters, and it can be used to selectively affect a specific type of virus.

We performed for the first time experiments on laser remote sensing of the moisture content of biological objects essential for the agricultural industry. Probing was carried out using a fluorescence lidar based on a pulsed solid-state laser (527 nm, 5 ns, 1 kHz, 200 μJ/pulse), developed at the Prokhorov General Physics Institute, Russian Academy of Sciences, and a gated intensified charge coupled device camera. The spectra of laser fluorescence of various biological objects of plant origin were recorded at different humidity values. The loss of water was accompanied by the degradation of biological pigments, causing an uneven increase in the intensity of bands in the fluorescence spectrum for different spectral ranges. The ratio of the spectral bands of chlorophyll a (680 nm) and protochlorophyllide (630 nm) has the best correlation with residual moisture, which opens up a promising direction for lidar measurement and monitoring of moisture/dry matter in silage or perennial grasses.

Low-frequency stimulated Raman spectra in suspensions of Alternanthera mosaic virus and Potato virus X are calculated and measured. The discrepancy between the calculated and measured frequencies of the Raman lines for the Potato virus X is attributed to the difference in the mechanical properties of the viruses, in particular, Young's modulus, in the native environment and when measured with an atomic force microscope. Differences are recorded in the stimulated Raman spectra of these viruses, allowing them to be identified.

Spectra of Raman scattering in the range of about 20 to 60 GHz are measured in Tris suspensions of the morphologically similar Alternanthera mosaic virus and potato virus X. Lines are observed whose frequency shift does not agree with the calculated values of the dominant vibrational modes in the mechanical model of the investigated virions as a single whole. These frequencies are related, in our opinion, to acoustical vibrations of functional groups of proteins and amino acids.

The excitation of stimulated scattering of laser radiation at several equidistant frequencies is observed in an aqueous suspension of hollow glass microspheres. The scattering spectrum is frequency-asymmetric. No stimulated Brillouin scattering, accompanying nonlinear processes in condensed media excited by narrowband laser pulses on the order of tens of nanoseconds, is detected. The observed features are interpreted in terms of stimulated scattering mediated by the whispering-gallery modes of glass microspheres.

Improving the laser-induced breakdown spectroscopy analysis of heterogeneous agricultural samples utilizing large laser spotting.