Marine particles investigation by underwater digital holography

A hardware-software complex for non-contact investigation of marine particles is presented. The complex is based on digital holography principles and can be immersed in water, for example, to study plankton in a habitat. Special features of a submersible holocamera (or DHC sensor) are considered. Results of approbation of the complex during the Mission in the Kara Sea are presented. A new DHC sensor design is discusse

Holography as a tool for advanced learning of optics and photonics

ABSTRACT Laboratory works on holograms recording, reconstruction and interpretation are useful for two reasons. Firstly, holography is widely used in science and engineering. Secondly, training labs in holography require complex applying of knowledge on interference, diffraction, coherency and other domains of optics. Educational kit and methodological instructions for optical experiments were presented in the previous paper 1 . The desktop holographic camera described in this paper is one of the additional functional units of the kit. The desktop holographic camera does not require additional protection against vibrations even if the exposure time is several minutes. This is a compact holographic installation for recording Denisyuk holograms. Two experiments are described in the paper to illustrate the usefulness of holographic laboratory works. The first one is a recording and reconstruction of a Denisyuk hologram. The second one is a recording and interpretation of a double-exposure interferogram when the holoplate is sagged due to loading between exposures. Also included in the paper are holographic setup and laboratory works on digital holography. These experiments require, in addition, complex applying of knowledge on photo receivers, CCD and other domains of photonics

Digital hologram as a display optical system

The holographic system is usually used for imaging, so it can be attributed to imaging optical systems. This analogy allows using a well-developed computational optics technique to design and analyze real digital holographic systems, as well as to solve the measuring tasks of digital holography. The work presents a mathematical model that establishes a one-to-one correspondence between dimensional and spatial parameters of a digital holographic image and a holographing object for the given case of an in-line scheme. The values of the model constants used to determine the real size and the longitudinal coordinate of an object according to its holographic image are found through calibration. The described approach is used to calibrate and analyze the imaging properties of a submersible digital holographic camera designed to study plankton in its habitat. The paper also shows the results obtained in situ using the holographic sensor of plankton

Digital holography of marine particles in situ during the Arctic Expedition

The paper presents the results of measurements of marine particles in situ during Arctic expedition using the digital holographic camera (DHC). Characteristics of various marine particles, including classification and statistics on taxa, depth profiles of plankton concentration were measured. DHC technology may be used without additional sensors to obtain additional information on the medium, such as volume content of methane according to bubble surfacing and water turbidity assessed by the screening coefficient of the suspension taxon

Phototropic response features for different systematic groups of mesoplankton under adverse environmental conditions

Current trends in the application of bioindication methods are related to the use of submersible tools that perform real- time measurements directly in the studied aquatic environment. The methods based on the registration of changes in the be- havioral responses of zooplankton, in particular Crustaceans, which make up the vast majority of the biomass in water areas, seem quite promising. However, the multispe- cies composition of natural planktonic biocenoses poses the need to consider the potential difference in the sensitivity of organisms to pollutants. This paper describes laboratory studies of the phototropic response of plankton to attracting light. The studies were carried out on a model natural community that in equal amounts includes Daphnia magna, Daphnia pulex, and Cyclops vicinus, as well as on the monoculture groups of these species. The phototropic response was initiated by the attracting light with a wavelength of 532 nm close to the local maximum of the reflection spectrum of chlorella microalgae. Standard potassium bichromate was used as the model pollutant

The effect of volume inclusions of the ZnGeP2 single-crystal on the dispersion of the refraction index and the absorption coefficient in mid-IR and terahertz ranges of wavelengths

Volume filamentary inclusions in ZnGeP2 have been visualized using the digital holography method. The chemical composition of the filamentous volume inclusions Zn3P2 and Ge have been determined using the method of X-ray diffraction analysis. It is shown that the presence of volume inclusions in the ZnGeP2 singlecrystal leads to an increase in the reflection coefficient in the region of 12.5 μm. The dispersion dependences of the refractive index and the absorption coefficient of the studied ZnGeP2 samples at wavelengths of 300–1000 μm in the region of non-fundamental absorption have been obtained. It has been shown that the presence of volume inclusions in a single-crystal leads to an increase in the refractive index in the entire THz range under study by the value of Δnmax = 0,0008. The difference between absorption coefficients for the studied samples varies from Δα = 0.1 cm 1 to Δα = 0.15 cm 1 depending on the wavelength

Underwater holographic sensor for plankton studies in situ including accompanying measurements

The paper presents an underwater holographic sensor to study marine particles—a miniDHC digital holographic camera, which may be used as part of a hydrobiological probe for accompanying (background) measurements. The results of field measurements of plankton are given and interpreted, their verification is performed. Errors of measurements and classification of plankton particles are estimated. MiniDHC allows measurement of the following set of background data, which is confirmed by field tests: plankton concentration, average size and size dispersion of individuals, particle size distribution, including on major taxa, as well as water turbidity and suspension statistics. Version of constructing measuring systems based on modern carriers of operational oceanography for the purpose of ecological diagnostics of the world ocean using autochthonous plankton are discussed. The results of field measurements of plankton using miniDHC as part of a hydrobiological probe are presented and interpreted, and their verification is carried out. The results of comparing the data on the concentration of individual taxa obtained using miniDHC with the data obtained by the traditional method using plankton catching with a net showed a difference of no more than 23%. The article also contains recommendations for expanding the potential of miniDHC, its purpose indicators, and improving metrological characteristics

Digital holography methods for visualization and identification of ZnGeP2 bulk defects

The volumetric filamentous inclusions in ZnGeP2 were visualized by digital holography, their characteristic sizes were determined, and their location in the sample volume was determined. The chemical composition of filamentous bulk inclusions – Zn3P2 and Ge-was determined by X-ray diffraction analysis. The influence of the second-phase inclusions (Zn3P2 and Ge) on the quasi optical characteristics (refractive index and absorption coefficient) in the resonant absorption band (12–12.5 microns) is established. The presence of bulk inclusions in the ZnGeP2 single crystal leads to an increase in the reflection coefficient in the region of 12.5 microns. The dispersion dependences of the refractive index and the absorption coefficient of the studied ZnGeP2 samples at wavelengths of 300–1000 microns in the non fundamental absorption region were obtained. The obtained experimental results confirm the assumption of the determining role of free carriers in the formation of dielectric losses in the wavelength range of 100–1000 microns. The hypothesis that one of the main sources of free carriers in ZnGeP2 is the matrix medium / inclusion interface of the second phase is confirmed.В ст. ошибочно: A. S. Bolshako

Errors in determining coordinates in the digital holography of particles

Based on the approach applied to diffraction-limited optical systems, the study evaluates the measurement errors of transverse and longitudinal coordinates of particle images reconstructed from digital holograms. The paper shows the experimental results of testing the above estimates

Assessment of fatigue damage to aircraft glass using digital holography methods

The purpose of this work is to test the digital holography method for determining the depth of fatigue surface defects of the "silver" type of aviation organic glass caused by cyclic mechanical overloads, as well as the impact of aggressive substances. To study the fatigue defects of aviation organic glass, a digital holographic camera was used, the configuration of which is an axial scheme for recording digital Gabor holograms. During the experiment, the possibility of using the digital holography method to determine the characteristic transverse dimensions of surface defects in aircraft glazing parts and longitudinal dimensions was shown. The work carried out and the created model of the digital holographic camera show the potential possibility of creating a method for checking with a given accuracy the elements of the aircraft glazing for the presence of surface damage and assessing their impact on flight safety