Branka Murić

Improving the holographic sensitivity of dichromated gelatin in the blue–green part of the spectrum by sensitization with xanthene dyes

The holographic properties of dichromated gelatin (DCG) sensitized with various xanthene dyes were studied, and results are reported. The sensitivity of dyed DCG in the green part of the spectrum compared with that of pure DCG (215 mJ/cm(2)) was significantly improved by addition of Rhodamine 6G (140 mJ/cm(2)) or Erythrosin B (90 mJ/cm(2)). Diffraction gratings were recorded with a He-Ne laser at 543.5 nm. The maximum diffraction efficiency was found to be 32% at normal incidence of the readout beam; it was 80% at the Bragg angle.

Real-time measurement of internal stress of dental tissue using holography.

We describe a real-time holographic technique used to observe dental contraction due to photo-polymerization of dental filling during LED lamp illumination. An off-axis setup was used, with wet in-situ processing of the holographic plate, and consequent recording of interference fringes using CCD camera. Finite elements method was used to calculate internal stress of dental tissue, corresponding to experimentally measured deformation. A technique enables selection of preferred illumination method with reduced polymerization contraction. As a consequence, durability of dental filling might be significantly improved.

Luminescence thermometry via the two-dopant intensity ratio of Y2O3:Er3+, Eu3+

In this work we investigated the photoluminescence properties of Y2O3:Er3+, Eu3+ as a function of temperature and the possibility to use this material as a temperature sensor. Photoluminescence emission measurements with 532 nm laser excitation were recorded in the temperature range from 303 up to 573 K. The measured intensity ratio of erbium 4S3/2 → 4I15/2 and europium 5D0 → 7F2 emission lines was used for determination of the temperature calibration curve. These emission lines are intense, narrow and well defined. The distance between the lines, being 47 nm, can be easily measured even with a low-resolution spectrometer. The calculated relative sensitivity of the temperature sensor was 1.4% K−1 at 303 K, in the physiological temperature range, meaning that it could be successfully applied in biological studies.

Thermal analysis of microlens formation on a sensitized gelatin layer

We analyze a mechanism of direct laser writing of microlenses. We find that thermal effects and photochemical reactions are responsible for microlens formation on a sensitized gelatin layer. An infrared camera was used to assess the temperature distribution during the microlens formation, while the diffraction pattern produced by the microlens itself was used to estimate optical properties. The study of thermal processes enabled us to establish the correlation between thermal and optical parameters.

Imaging properties of laser-produced Gaussian profile microlenses

Microlens and microlens arrays have been successfully produced using sensitized gelatin and Nd:YAG laser at 532 nm. Obtained microlenses are divergent (negative), with parabolic profile and 600 &mgr;m useful aperture diameter. Microlenses have near diffraction limited performance with resolution more then 50 cycles/mm for the total field of view (2&ohgr; = 18°). Single microlens is manufactured in just a few seconds using 60 mW unfocused Nd:YAG laser beam.

Holographic Measurement of a Tooth Model and Dental Composite Contraction

We have developed a real-time holographic technique to observe deformation induced by dental composite contraction. The standard split beam method was used, in conjunction with in situ holographic plate processing. Experiments were performed on a mechanical model of a human tooth with cavity. A silicone mold was used to manufacture a number of identical casts, using photoactivated composite. A LED lamp was used to induce photo-polymerization reaction in a composite. We have shown that the proposed method is ideal to analyze various polymerization strategies, with the purpose of recommending one which minimizes the polymerization contraction.

Sensitized gelatin as a versatile biomaterial with tailored mechanical and optical properties

Abstract We have found that gelatin doped with tot’hema (medication used for curing anemia) andeosin becomes elastic, while retaining good optical properties. The mechanical properties oftot’hema–eosin-sensitized gelatin films (TESG) have been investigated for variousconcentrations of tot’hema (ranging from 5 to 30% v/v). TESG specimens were preparedaccording to the ASTM standards for elastic materials. Tensile strength, strain at break andYoung’s modulus were measured. The results show that the extensibility of TESG filmincreases with increasing tot’hema concentration, while the Young’s modulus and stress atbreak exponentially decrease. Mechanical properties can be tailored to suit various biomedicalapplications such as blood vessels, human lens capsules and biosensors based on microlenses.Tunable (strain responsive) TESG microlenses were produced and a mechanical model ofblood vessels was prepared.PACS numbers: 42.70.Jk, 81.40.Jj, 87.85.J−, 87.85.fk(Some figures may appear in colour only in the online journal)

Biomechanical model produced from light-activated dental composite resins: a holographic analysis

Light-activated dental composites, commonly applied in dentistry, can be used as excellent material for producing biomechanical models. They can be cast in almost any shape in an appropriate silicone mold and quickly solidified by irradiation with light in the blue part of the spectrum. In that way, it is possible to obtain any number of nearly identical casts. The models can be used to study the behavior of arbitrary structure under mechanical loads. To test the technique, a simple mechanical model of the tooth with a mesio–occluso–distal cavity was manufactured. Composite resin restoration was placed inside the cavity and light cured. Real-time holographic interferometry was used to analyze the contraction of the composite resin and its effect on the surrounding material. The results obtained in the holographic experiment were in good agreement with those obtained using the finite element method.