Coherence Properties Of Laser Light Research Articles

Simultaneous high-resolution and wide-field microscopy with improved image sharpness using pseudo-thermal light source and Fourier Ptychography

Lasers have been widely used in areas such as interferometry, imaging, holography, projection displays, etc. as they provide the benefit of high spatio-temporal coherence and high brightness along with the formation of speckles. High spatio-temporal coherence is a remarkable property of laser due to which interferometry and holography can be easily implemented, but the occurrence of spurious fringes due to multiple reflections and the formation of speckles reduces the quality of images in laser-based systems. Here, we present the implementation of Fourier Ptychography using pseudo-thermal light source. The spatial and temporal coherence properties of laser light have been reduced using a static and rotating diffuser leading to the implementation of pseudo-thermal light source. The use of pseudo-thermal source leads to an increase in image sharpness and decrease in speckle contrast thus acting as a suitable source for imaging. The improvement in experimental results suggests that both high temporal coherence and low spatial coherence is necessary for high contrast imaging with improvement in spatial resolution. The pseudo-thermal light source acts as a solution to non-uniform illumination with higher sharpness and higher brightness compared to spatially and temporally incoherent LED array light source. Experiments have been carried out on biological samples to prove the effect.

A Comparative Study of 660 nm Low-Level Laser and Light Emitted Diode in Proliferative Effects of Fibroblast Cells.

Introduction: In recent years, low-power lasers have been widely used in medicine. With the introduction of affordable light emitted diode (LED), clinical application of LED light has become more and more popular. However, some researchers believe that due to lack of coherence of the LED light, it can be different in terms of biological effects, in comparison with laser. In this study, the biological effects of low-level laser (LLL) to those of LED light are compared and discussed. Methods: Human skin fibroblast cell line Hu02 was irradiated with LLL and LED light with a wavelength of 660 nm, power output of 35 mW and in continuous mode and the control group was not irradiated. The biological effects were compared through analysis of cell proliferation, production of reactive oxygen species (ROS) within the cell and rate of cell division. Results: Our findings showed that production of ROS within the cell was linearly increased both in the LED and laser light irradiated cells. However, laser light is more incremental in comparison to LED light. The MTT results showed that laser light at low energy density (less than 5 J/cm2) increased the rate of cell proliferation after 24 hours. Although, the rate of cell division was increased in energy density of 1 J/cm2 compared to the control group, this increase was not statistically significant. Discussion: The findings indicated that the coherence properties of laser light provided more energy for the cells, and in a constant energy density, laser light created more oxidative stresses in comparison with LED light.

Ultrafast laser control of electron dynamics in atoms, molecules and solids

Exploiting coherence properties of laser light together with quantum mechanical matter interferences in order to steer a chemical reaction into a pre-defined target channel is the basis of coherent control. The increasing availability of laser sources operating on the time scale of molecular dynamics, i.e. the femtosecond regime, and the increasing capabilities of shaping light in terms of amplitude, phase and polarization also on the time scale of molecular dynamics brought the temporal aspect of this field to the fore. Since the last Faraday Discussion (Faraday Discussion 113, Stereochemistry and control in molecular reaction dynamics) devoted to this topic more than a decade ago a tremendous cross-fertilization to neighbouring "quantum technology disciplines" in terms of experimental techniques and theoretical developments has occurred. Examples are NMR, quantum information, ultracold molecules, nonlinear spectroscopy and microscopy and extreme nonlinear optics including attosecond-science. As pointed out by the organizers, this meeting brings us back to chemistry and aims to assess recent progress in our general understanding of coherence and control in chemistry and to define new avenues for the future. To that end we will in the Introductory lecture first shortly review some aspects of coherent control. This will not be fully comprehensive and is mainly meant to give some background to current experimental efforts of our research group in controlling (coherent) electronic excitations with tailored light fields. Examples and perspectives for the latter will be given.

Coherence and intensity moments of laser light

Taking the modal behaviours of the laser field into account, the coherence properties of laser light can be characterized by mode coherence functions (MCFs) and mode coherence coefficients (MCCs). Changes in laser light properties due to optical operations can be described by transformation laws for the MCFs and the MCCs. The transformation laws as well as transformation matrices for propagation in free space, phase transformations, spatial amplitude modulations and aperturizing are given. Furthermore, intensity distributions and intensity moments in the spatial and in the spatial frequency domains are expressed in terms of the MCCs. General expressions for the beam quality factors,M2s, obtained using the intensity moments and some useful expressions for intensity moments of higher order are discussed.

The effect of wavefront curvature on the coherence properties of laser light scattered by target centres in uniform motion

Moving speckle phenomena produced in the presence of wavefront curvature when laser light is scattered by an assembly of uniformly moving target centres are investigated. The first- and second-order space-time correlation functions of the scattered radiation are calculated and it is shown that the conditions for cross-spectral purity are not satisfied. It is pointed out that the effects offer a means of measurement of the velocity of the scatterers.

Light Scattered by a Liquid Crystal: a New Quasi-Thermal Source

The spatial and temporal coherence properties of laser light scattered by a liquid crystal cell under the application of an external dc field are studied. It is shown that the scattered field constitutes a source with very long coherence time. The coherence time can be changed by changing the value of the applied voltage, and the spatial coherence can be adjusted by varying the dimension of the illuminated spot on the cell. The effects produced when the length of correlation of fluctuations in the liquid crystal is not negligible with respect to the dimension of the spot in the cell are also studied. The scattered field is proposed as a new quasi-thermal source, alternative of the rotating ground glass disk.

Laser Optics Experiments and Demonstrations

Several demonstrations or experiments illustrating the coherence properties of laser light are described. In addition, a summary is given of demonstrations in interference and diffraction which make use of the high intensity of a laser source. These are discussed specifically within the capabilities of a 0.1-mW laser, the size that is most likely to be available for teaching in an average physics department.