Theoretical and experimental study of optical diffractometry based on Fresnel diffraction from a transmission phase step.

We present experiments to study the optical diffractometry of Fresnel diffraction from transmission phase steps under illuminating sources with distinct spatial profiles. The experimental results are extended analytically with the Fresnel Gaussian shape invariant introduced in previous publications to calculate the propagation of a coherent illuminating source through optical setups. We use a narrow coherent illuminating source to permit extending the applicability of the method for clinical purposes and perform calculations with illuminating sources with different spatial profiles, including a non-diffracting Airy beam, to allow for the establishment of general sensitivity formulae within the paraxial region.

Quantitative Photoacoustic Method for the Measurement of Absorption Coefficients of Highly Absorbing Samples.

In this study, we present a quantitative photoacoustic (PA) method for performing absorption measurements on highly absorbing samples. Based on the thermoelastic mechanism, the relative changes in PA signal amplitude allowed the determination of absorption coefficients of materials in the 0.19-2500-cm-1 range, with no prior knowledge of the material's optoacoustic properties required. We have tested our new methodology by performing absorption measurements on a series of planar liquid samples as well as gelatinized spherical samples. In this approach, laser-induced ultrasound waves were detected in transmission mode. With the model presented herein and a measurement of the relative change in amplitude of the PA signal at two different known concentrations, the absorption coefficient of the sample can be straightforwardly extracted. Three important advantages are highlighted by this analytical approach. First, no previous knowledge of the optical or acoustic properties of the sample is necessary. Second, only a small quantity of sample is required. Finally, our methodology includes both short- and long-pulse regimes, validating its use for any laser pulse duration so long as the requirement for thermal confinement is fulfilled. Remarkably, this new methodology performs best for thick, highly absorbing samples where traditional spectrophotometry is most challenging and unreliable, offering a promising alternative for quantification of the absorption properties of a range of diverse liquid, and gelatinous-state materials not amenable to conventional methods.

Gaussian beam with high spherical aberration focused by a singlet lens-shaped container for glucose measurements.

We describe a highly sensitive optical technique for glucose concentration measurements in liquid samples based on measuring the heights of the primary sidelobes of the normalized intensity profiles of a focused Gaussian beam with high spherical aberration. A singlet lens-shaped container, filled with the sample under test, is used to focus the beam at an observation plane placed close to the focusing region. The normalized intensity profile of the aberrated beam allows for accurate measurement of the sample glucose concentration.

Spectrophotometric analysis at the single-cell level: elucidating dispersity within melanic immortalized cell populations.

It is widely held that the melanosome is an exemplar of the absorption features of melanin-containing cells, which are assumed to be uniform in both size and optical characteristics. In recent years, however, it has become increasingly apparent that this is a strikingly poor assumption. Indeed, melanin extracted from natural sources and synthetic melanin both show wide variability in their degree of polymerization (molecular weight) and spectroscopic characteristics. In the current study, imaging spectrophotometry performed on individual cells of immortalized melanin-producing cell lines revealed broad distributions in their sizes: 9.5-36.2 µm for Hs936 human melanoma cells, 10.9-20.8 µm for T47D human breast cancer cells, 5.3-43.5 µm for B16F1 mouse melanoma cells, and 6.4-54.2 µm for B16F10 mouse melanoma cells. The color appearance (from translucent to yellow to nearly black), absorption spectrum, and absorption (extinction) coefficient at 532 nm (28.73 to 364.75, 0.01 to 40.17, 5.88 to 977.19, and 0.01 to 1120 cm-1 for Hs936, T47D, B16F1, and B16F10 cells, respectively) of an individual cell also vary widely and cannot be adequately described by a 'typical' value. In comparison, human red blood cells are much more uniform in size (6.0-8.1 µm diameter; 1.9-3.2 µm thickness), although they too show a broad range of absorptivities, with extinction coefficients in the range of 65 to 370 cm-1 when measured at 532 nm. To further evaluate the impact of these findings on photoacoustic bioanalysis, we performed simulations of the generation of photoacoustic signals expected from these cell types. These simulations revealed that their variation in optical features exerts a pronounced effect on the amplitude and shape of the photoacoustic signals generated from these cell types. Finally, we compared the photoacoustic signal generated from these cells under ideal conditions (i.e., a single cell in isolation) versus a heterogeneous real-world sample, demonstrating that when a single or few cancer cells are present within a blood droplet, the photoacoustic signal is indistinguishable from that measured from blood alone. These outcomes have important ramifications for the early photoacoustic detection of cancer cells and circulating tumor emboli, while pointing to the potential of single-cell imaging spectrophotometry to assess heterogeneity within cell populations in more quantitative terms.

Refractive index and geometrical thickness measurement of thin optical samples by a transmitted Gaussian beam.

We describe a technique for simultaneously measuring the local geometrical thickness and the refractive index of semi-transparent thin plates by means of the diffractive properties of a transmitted Gaussian beam. The technique is based on measuring the semi-width of the transmitted beam and the shift of the Gaussian centroid caused by introducing a tilt on the sample under test. A homodyne technique is devised to accurately characterize the Gaussian beam. Our proposal does not require any prior information of the sample under study. We present analytical support of our technique and we give experimental results.