Jahja O. Kokaj

Equivalence of two approaches to the design of optically realizable correlation filters

For the design of optically realizable correlation filters, two apparently different methods, the minimum Euclidean distance optimal filters and the multicriteria optimal trade-off filters have been proposed. In this paper, the equivalence of these two approaches is established by considering the operating regions that include the origin and figures of merit that include the detector noise.

Cs2 ‘diffuse bands’ emission from superheated cesium vapor

Thermal emission from superheated cesium vapor was studied to very high temperatures from 700 °C to 1000 °C. This was performed in the vapor condition only and with no liquid cesium present in the all-sapphire cell. We observed a number of atomic and molecular spectral features simultaneously in emission and absorption, especially peculiar thermal emission of cesium dimer diffuse bands (2 3Πg → a 3∑u + transitions) around 710 nm coexisting with absorption bands around first resonance lines at 852 and 894 nm. We performed appropriate calculations of the diffuse band emission profiles and compared them with measured profiles. We also performed absorption measurements and compared observed diffuse band profiles with calculated ones. Possible applications of the observed phenomena will be discussed in terms of the solar energy conversion using dense cesium vapor.

Structured photoionization continuum of superheated cesium vapor

We studied the absorption spectrum of dense cesium vapor in an all-sapphire cell with a special emphasis on the highly structured photoionization continuum. This continuum appears to be composed of atomic and molecular contributions which can be separated by means of additional superheating of the cesium vapor in the sapphire cell. This was possible due to the small amount of cesium filling which completely evaporated at a temperature of around 450 °C. This enabled the overheating of cesium dimers which greatly reduced its concentration at a temperature of 900 °C, leaving almost pure atomic Cs vapor. The analysis of the thermal destruction indicated that the highly structured molecular component of the photoionization continuum can be entirely attributed to cesium dimers. We discuss the possible origin of the structured photoionization continuum as stemming from the absorption process from the ground state of the Cs2 molecule to the doubly excited Cs2** molecule located above Cs2+ molecular ionization limit. The corresponding potential curves are subjected to mutual interactions and autoionization.

Higher-moment and diffraction-order computation for deformation measurement

Higher moment and diffraction orders are computed and used for deformation measurement. For a given two-dimenstional function lower-order moments are calculated. It is shown that simplified results can be obtained if an appropriate pattern is used for the calculation. The obtained results are employed for calculation of higher-order mements. Optical implementation and their use for deformation measurement is shown. High diffraction orders are introduced by using a projected grill-pattern on the model surface. This is performed by selecting higher frequency spots in the Fourier-Transform plane. Selection of the high-frequency diffraction orders and calculation of high-order moments are two image processing approaches useful for deformation measurement. Accuracy of the measurement for in-plane deformation and out-of-plane rotation is calculated. It is shown that accuracy of measurement is increased when higher orders are used.

Morphological image processing of a bubble in laser-induced shock-wave lithotripsy

In this work, morphological processing is applied to study a bubble, which is crucial factor in laser-induced shock-wave lithotripsy. Erosion, dilation and subtraction are applied for edge detection of a bubble Hence the position and the shape is measured. The image of the bubble is extracted from the actual image of the stone (shadowgram). The image is obtained by fast photography using an N-Dye laser for illumination. A Ho:yag laser is used for fragmentation of the stone. Using a time delay, an oscilloscope and a computer, two laser pulses are synchronized. A microscope and a Kodak-camera are used to photograph the stone and the phenomena around.

Gallbladder stone inspection and identification for laser lithotripsy

Using high speed imaging techniques, the gall bladder stone immersed in liquid is detected and identified. The detection of the shock waves induced by laser power is reached by using interferometry technique. Using gall bladder and tissue images obtained by ultra-fast photography and time resolved laser fluorescence the correlation of correlation is performed. The tissue image is used to perform the correlation filter. Hence lower correlation output is used for firing of the laser power.

Femtosecond laser fluorescence and propagation in very dense potassium vapor.

Femtosecond (fs) laser propagation and fluorescence of dense potassium vapor was studied, and the spectral region around the first and the second doublets of the principal series lines of potassium atoms was investigated. In our search we did not observe the conical emission in the far field, although it was previously observed in the case of rubidium. We discuss the possible reason of this unexpected result. The fluorescence spectrum revealed Rb impurity resonance lines in emission due to the collisional redistribution from the K(4p) levels into the Rb(5p) levels. In the forward propagation of 400 nm femtosecond light we observed the molecular band red shifted from potassium second doublet. However, no molecular spectrum was observed when the mode-locked fs laser light was discretely tuned within the wings of the first resonance lines, at 770 nm.

Identification of discontinuities in plasma plume evolution

The ejection of material during laser ablation gives rise to the development of discontinuities in the ambient gas. Several of these discontinuities are observed and characterized, including externally and internally propagating shock waves, contact surface, and the ionization front. Qualitative experimental observations and analysis of these discontinuities are presented. Results from shadowgraphy enabled determination of an irradiance threshold between two different ablation mechanisms, and determination of several stages of plasma plume evolution. Consideration of the refractive index as a dynamic sum of the contributions from gas and electrons led to separate identification of ionization front from the contact surface. Furthermore, ionization front was observed to lead the shock wave at the earlier stage of the ablation.

Visualization of ultrafast phenomena during the laser-induced lithotripsy

Optical coherent techniques, inteferometry and microscopy are applied for visualization of phenomena associated with laser-based lithotripsy. Shadowgraphy and ballistic imaging is used to visualize the phenomena generated around a stone during the action of a laser pulse. Results are confirmed using optical and electron microscopy.

Microscopy of phenomena akin to laser lithotripsy

An unconventional microscopy is applied to visualize and measure the phenomena during the laser-based destruction of a stone. By using the ultra-fast microscopic technique and shadowgraphy, some unknown phenomena akin to the laser lithotripsy are studied.