A mechanical beam chopper consists of a rotating disc of regularly spaced wide slits which allow light to pass through them. A continuous light beam, after passing through the rotating disc, is switched-on and switched-off periodically, and a series of optical pulses are produced. The intensity of each pulse is expected to rise and fall smoothly with time. However, a careful study has revealed that the edges of mechanically chopped laser light pulses consist of periodic intensity undulations which can be detected with a photo detector. It has been shown in this paper that the intensity undulations in mechanically chopped laser pulses are produced by diffraction of light from the rotating disc and a detailed explanation of the intensity undulations is given. The experiment provides an efficient method to capture a one dimensional diffraction profile of light from a straight sharp-edge in the time domain. In addition, the experiment accurately measured wavelengths of three different laser beams from the undulations in mechanically chopped laser light pulses.

Voltage current characteristics of a PN-junction diode are intrinsically nonlinear in nature. It is shown in this paper that a mathematical form of nonlinearity of a PN-junction diode resembles the nonlinear response of electric polarization of a dielectric medium to the electric field. Nonlinearity of a PN-junction can be expressed in a series of successively increasing orders of the nonlinearity. For a PN-junction diode, higher order nonlinear terms become significant as a voltage across the diode is increased. In this paper, a gradual emergence of a nonlinear regime with the amplitude of a sinusoidal voltage is presented. Higher order harmonics are produced by utilizing the nonlinearity of a single PN-junction diode. An experimental realization of a frequency comb with the highest frequency up to the twentieth harmonics is also presented. In addition, in the same circuit by making the nonlinearity significant up to the second order, an experiment on generation of the sum and difference of frequencies is realized.of linear and nonlinear terms. With an increase in the amplitude of a sinusoidal voltage applied across a PN-junction diode the higher order nonlinearities become important. As the amplitude of a sinusoidal voltage is increased, new components of frequency appears in current passing through the PN-junction diode. A gradual generation of new frequencies and generation of a frequency comb [ Hansch (2006)] with the highest frequency up to the twentieth harmonics are clearly demonstrated in the experiment. Further, by using a source of two different frequency sinusoidal voltage waveforms (a sinusoidal voltage has a wave like form in the time domain), the sum and difference frequency generation have been demonstrated experimentally.

In this paper, an experiment of quantum diffraction of position-momentum entangled photons from a straight sharp edge is presented. Path of a single photon of an entangled pair is partially blocked by a sharp edge whereas the other photon is detected at a stationary location without revealing the which-path information of the other photon. Quantum diffraction pattern of the sharp edge is revealed only in the correlated conditional detection of spatially separated photons and no diffraction pattern is formed in local detections of individual photons. Theoretical analysis of the quantum diffraction of position-momentum entangled photons from a sharp edge is also presented in this paper. Experimental measurements of the quantum diffraction pattern are compared with theoretically calculated quantum diffraction pattern of position-momentum entangled photons.Interference of a single particle with itself is a true manifestation of principle of quantum superposition. A single photon exhibits interference in a double slit experiment, if no which-path information of its passage through a double slit is available. If this photon is quantum entangled with another photon such that it carries the whichpath information of the former photon, then a single photon interference is not formed. However, an interference pattern can be recovered selectively from a smeared pattern by making measurements of photon quantum state in a path superposition basis and correlating it with detection of the other photon on the screen. In this type of conditional and selective detection of individual photons, interference manifests a global nature of quantum entanglement by which amplitudes of both photons interfere, even if only one of them has passed through the double slit. This feature of quantum entanglement has been demonstrated in quantum ghost interference experiments [1][2][3][4][5]. In quantum ghost interference selection is naturally linked to location of detection of a photon. Based on coincidence detection, experiments of ghost imaging have been performed [6][7][8][9][10][11]. Quantum interference is also shown in an experiment consisting of a delocalized double slit [12,13]. Similar experiments considering EPR [14] pairs of entangled atoms have been proposed [15]. From a foundational perspective of quantum physics, interesting thought provoking experiments have been reported on quantum erasure of path information showing global interference of quantum amplitudes of entangled photons [16][17][18][19][20][21][22][23].In this paper, an experiment on quantum diffraction of position-momentum entangled photons from a straight sharp edge is presented. Diffraction of classical electromagnetic waves is known since the beginning of Huygens-Fresnel theory of diffraction however, a first rigorous theory of diffraction of classical light from an edge was given by A. Sommerfeld [24]. Diffraction of classical light from a straight sharp edge [25][26][27][28][29], often regarded as a precursor of diffraction, has been intensively explored.In an exper...

Cascaded spontaneous parametric downconversion is used to produce entangled photon triplets, although poor efficiency limits rates. As a solution, we propose trapping photons in an active cavity, giving them many chances at downconversion.

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