Ultraviolet radiation emitted by compact fluorescent lamps

To meet the objective of energy efficiency, increasing emphasis on use of energy saver compact fluorescent lamps (CFLs), makes it necessary to analyze the effect of radiation especially ultraviolet (UV) radiation on human health. Various types of CFLs in terms of various shapes, sizes and electrical powers are studied for UV content present in their radiation. Various parameters such as UV irradiance, ratio of UV irradiance to electrical power (η) and ratio of UV power to luminous flux (k), for eighteen types of CFLs are studied to dictate their performance. As expected, both the UV output power and the luminous flux are reduced in the case of double envelope CFLs in comparison to single envelope CFLs, however, the k value is reduced more effectively. For all types of CFLs under study, k1 for UVA remains less than 104 µW/lm, which is a safe limit for UVA. However, the study demonstrates that the use of CFLs might be detrimental to human health if these are used at shorter distance, e.g., in table lamps

Experimental study of wavefront distortion in the dark hollow beam generated using axicon

Axicons are the optical components widely used for the generation of dark hollow beam in a controlled manner. In certain circumstances, distortion in the transverse intensity profile (i.e. wavefront distortion) appears in DHB produced by axicon-lens assembly. In this paper, we performed the detailed experimental study for exploring the reasons for the appearance of wavefront distortion including its control and removal in partially coherent dark hollow beam produced from axicon-lens assembly. This experimental study find its crucial importance in the applications, where axicon is used for producing dark hollow beams, e.g. in eye surgery, atom trapping, laser machining and laser resonator. We also observed that the effect of chromatic aberration near the region of induced wavefront distortion in the depth of focus changes with propagation and can be controlled by varying spatial coherence of the beam. This control on the effect of chromatic aberration will be helpful in attaining achromatic dark hollow beam from axicon

Upgradation of a Spectral Irradiance Measurement Facility at National Physical Laboratory, India

This report describes the details of a recently upgraded spectral irradiance measurement facility in optical radiation standards at National Physical Laboratory, India. This facility provides the calibration of spectral irradiance in the wavelength range 280 nm - 2500 nm. PTB, Braunschweig, Germany calibrated five numbers of 1000 W quartz halogen lamps, which are used as reference standards for spectral irradiance scale. In addition to providing the details of instruments, the procedure of calibration and evaluation of uncertainties is also described. For checking the fidelity, repeatability and reproducibility of the upgraded system, calibration of one of the PTB calibrated lamps, was done against the other four PTB calibrated lamps. These measurements not only provide confidence on the upgraded system but also verify the retention of the PTB certificate values after a lapse of two years after their calibration

Experimental realisation of parallel optical logic gates and combinational logic using multiple beam interference

In this paper, we report the experimental realisation of parallel optical logic gates and some combinational logic using multiple beam interference in three cascaded Michelson type interferometers. Considering light intensity at different points of 2-D interference pattern of four input laser beams as output, (i) two input AND, OR, NAND, NOR, XOR, XNOR optical logic gates in parallel, (ii) three input AND and NAND optical logic gates in parallel, and (iii) four input AND logic gate as well as some combinational logic in parallel were realised. By controlling the four input laser beams electro-optically or all-optically using nonlinear optical materials having large nonlinearity and fast response time, ultrafast photonic information processing can be performed utilizing present scheme due to parallel operation of large number of logic gates