The role of the temporal profile of femtosecond lasers in obtaining the holograms is uncovered when two lasers of different colours are used to produce the fringes and recording of holograms. It was shown that the contrast of the time average interference pattern of two short light pulses (pulse duration T ) of different colours is remarkably high for frequency detuning < 2π T (see Odoulov S. et al., Nat. Commun., 6 (2015) 5866). However, we prove that such a continuous range of frequency detuning is not possible but null regions develop and frequency bands are observed for realizing holograms if there is a deviation of the lasers from their Gaussian profiles. The increased pulse duration leads to the generation of additional frequency bands and their narrowing along with higher modulation depth. A shifting of the null regions is noticed for the lasers having different skewness and/or pulse duration.

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For the scheme of two colour lasers in interference and holography, we uncover remarkable contribution of focusing region (spread) of the peak intensity of superposing laser beams based on the numerical studies and confirm it by mathematical calculations. The pulses having peak intensity for a wider region create better interference pattern, leading to higher modulation depth. Also, such beams having a stronger intensity gradient enhance the range of frequency detuning (difference), which would ease the experimentation in getting better holograms. A comparison of the results achieved with such beams is done with the most commonly used Gaussian beams for the better understanding of the concept for the advancement in holography.

This paper presents the computational investigation of air flow over an aircraft at realistic speeds while demonstrating the importance of extending the existing analysis to the complete airplane and how pivotal it is in improving its in-flight performance. The study is done for F16 and F22 aircraft using ANSYS Fluent (19.2) to obtain pressure distribution, shear stress distribution and temperature variation on the complete surface of the aircraft. Since the front section of the aircraft is prone to direct initial impact of surrounding environment, this portion is also examined. Here, as the speed is doubled from Mach 1 to Mach 2, a rise in the value of all the three variables is noticed for the F16 aircraft, whereas the pressure distribution for F22 aircraft shows strange behaviour for the highest speed (Mach 2). On comparing the results over the whole surface, it is seen that F16 experiences smaller pressure (29% lower for Mach 1 and 30% for Mach 2), temperature (9.5% lower for Mach 1 and 30% for Mach 2) and shear stress relative to F22 and the stress shows a huge change (90% lower for Mach 1 and 83% for Mach 2). Results of the present study imply that the design of the aircraft highly influences its performance as the parameters discussed touch their limits.

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