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Type-I spontaneous parametric down-conversion using supercontinuum optical vortex beam

Abhijit Roy, Ali Mohebi, Erik Nicolai Christensen, Patrick Bowen Montague, Crislane de Brito, Sylwia M. Kolenderska, Piotr Leszek Kolenderski, Aurèle J. L. Adam, Enrico Conca, Simone Tisa, Ole Bang, Niels Israelsen

Published Jun 26, 2026• 0 citations
Publisher

Abstract

An optical vortex (OV) beam is a singular beam with a helical wavefront and a spatially varying phase profile, whereas spontaneous parametric down conversion (SPDC) is a well-established process of generating two-photon state of light. Here, we report photon generation via SPDC using a supercontinuum (SC) beam and a SC OV beam as pump. Specifically, we report generation of an integer charge SC OV beam with a spectral range of 420-480 nm by illuminating a narrow-band spiral phase plate (SPP) designed for 467 nm with a SC light beam of 390-500 nm spectral range. The broad bandwidth of the generated SC OV beam is confirmed using bandpass filters, and cylindrical lens based measurement is adapted to estimate the topological charge of the beam. The mode purity of the generated SC OV beam is determined by analysing its complex field, measured using a Mach–Zehnder interferometer. Besides, generation of fractional OV beam is observed around 400 nm, and the results are compared to the case of using a CW laser operating at 405 nm. In addition, we report generation of photon pairs via SPDC by pumping a β-BBO crystal with the SC beam and the integer charge SC OV beam. The down-conversion of the SC beam with a spectral range of 60 nm is confirmed using bandpass filters in the pump beam and recording the SPDC signal. A similar measurement is also conducted using the generated CW fractional OV beam. This investigation is expected to be useful in quantum imaging applications, where exploring new ways of generating photons and entanglement is of increasing interest.

DOI
10.1364/opticaopen.32787486.v1

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An optical vortex (OV) beam is a singular beam with a helical wavefront and a spatially varying phase profile, whereas spontaneous parametric down conversion (SPDC) is a well-established process of generating two-photon state of light. Here, we report photon generation via SPDC using a supercontinuum (SC) beam and a SC OV beam as pump. Specifically, we report generation of an integer charge SC OV beam with a spectral range of 420-480 nm by illuminating a narrow-band spiral phase plate (SPP) designed for 467 nm with a SC light beam of 390-500 nm spectral range. The broad bandwidth of the generated SC OV beam is confirmed using bandpass filters, and cylindrical lens based measurement is adapted to estimate the topological charge of the beam. The mode purity of the generated SC OV beam is determined by analysing its complex field, measured using a Mach–Zehnder interferometer. Besides, generation of fractional OV beam is observed around 400 nm, and the results are compared to the case of using a CW laser operating at 405 nm. In addition, we report generation of photon pairs via SPDC by pumping a β-BBO crystal with the SC beam and the integer charge SC OV beam. The down-conversion of the SC beam with a spectral range of 60 nm is confirmed using bandpass filters in the pump beam and recording the SPDC signal. A similar measurement is also conducted using the generated CW fractional OV beam. This investigation is expected to be useful in quantum imaging applications, where exploring new ways of generating photons and entanglement is of increasing interest.
An optical vortex (OV) beam is a singular beam with a helical wavefront and a spatially varying phase profile, whereas spontaneous parametric down conversion (SPDC) is a well-established process of generating two-photon state of light. Here, we report photon generation via SPDC using a supercontinuum (SC) beam and a SC OV beam as pump. Specifically, we report generation of an integer charge SC OV beam with a spectral range of 420-480 nm by illuminating a narrow-band spiral phase plate (SPP) designed for 467 nm with a SC light beam of 390-500 nm spectral range. The broad bandwidth of the generated SC OV beam is confirmed using bandpass filters, and cylindrical lens based measurement is adapted to estimate the topological charge of the beam. The mode purity of the generated SC OV beam is determined by analysing its complex field, measured using a Mach–Zehnder interferometer. Besides, generation of fractional OV beam is observed around 400 nm, and the results are compared to the case of using a CW laser operating at 405 nm. In addition, we report generation of photon pairs via SPDC by pumping a β-BBO crystal with the SC beam and the integer charge SC OV beam. The down-conversion of the SC beam with a spectral range of 60 nm is confirmed using bandpass filters in the pump beam and recording the SPDC signal. A similar measurement is also conducted using the generated CW fractional OV beam. This investigation is expected to be useful in quantum imaging applications, where exploring new ways of generating photons and entanglement is of increasing interest.
Spontaneous Parametric Down-conversion (SPDC) is now routinely used to generate photon pairs for imaging, spectroscopy, and quantum information and metrology. However, the peculiar spectro-spatial properties of SPDC beams are not always known from the largest audience: they can give rise to ring-like beams, depending on the temperature, the wavelengths and pump focusing. This has to be considered for imaging or long-range applications. We will show examples of such beams created in 532-pumped PPLN or PPKTP and 1064-nm-pumped PPLN crystals. With a simple model of noncolinear phase matching we will give physical insight into the phenomena and explain the role of the signal/idler group delay. We will also explain how aperiodic crystals could be useful.
We show that an optical vortex beam, implemented classically, can be transferred to the transverse amplitude of a heralded single photon. For this purpose we have relied on the process of spontaneous parametric downconversion (SPDC) for the generation of signal and idler photon pairs, using a pump in the form of a Bessel-Gauss (BG) beam with orbital angular momentum (specifically, with topological charge l = 1 and l = 2). We have designed our source so that it operates within the short SPDC crystal regime for which, the amplitude and phase of the pump may be transferred to a heralded single photon. In order to verify the vortex nature of our heralded single photon, we have shown that the conditional angular spectrum and the transverse intensity at the single-photon level match similar measurements carried out for the pump. In addition, we have shown that when our heralded single photon is diffracted through a triangular aperture, the far-field single-photon transverse intensity exhibits the expected triangular arrangement of intensity lobes associated with the presence of orbital angular momentum.
Summary form only given. Spontaneous degenerate parametric scattering [down-conversion] is a 3-photon process with one pump photon of frequency 2/spl omega/ and two output photons of frequency /spl omega/. We report the experimental observation of the down conversion with the optical vortex serving as a pump beam. An optical vortex is defined as a beam containing a phase singularity, i.e. The change of phase around the center of the beam equals 2 /spl pi/m; where the integer m is the topological charge. Each photon in the vortex beam possess orbital angular momentum L=m/spl planck/. The law of conservation of angular momentum is expected to be valid in a homogenous linear or nonlinear medium. Topological charge conservation was confirmed in second-harmonic generation experiments, and may be expected to hold under degenerate parametric scattering. However, in the quantum domain, the uncertainly relations, /spl Delta//spl phi//spl Delta/N>2/spl pi/, (where /spl phi/ is the phase and N is the number of photons) provides an opportunity to violate this conservation principle, since the phase of the two down-converted photons is undetermined to within /spl Delta//spl phi/=2/spl pi//2 for every converted fundamental photon. That is, the down converted signal may contain no information about the topological phase of the pump beam. Based on our experiments and numerical calculations of the down-converted signal we suggest that the phase information is indeed lost under down conversion, therefore violating the conservation of topological charge.
The generation and detection of nonclassical light of about 2 μm has good potential in an emerging field of high-sensitivity metrology, especially gravitational wave detection, as well as free-space quantum communication. A pair of photons is generated through a spontaneous parametric down-conversion (SPDC) process in a nonlinear optic crystal, which can be properly entangled in a spatial region where two beams with each polarization overlap or in a Sagnac-loop interferometer configuration. We investigated theoretically and numerically Type II SPDC in a potassium niobate (KNbO3, KN) crystal, which is useful as a material platform for generating photon pairs of high spectral purity in the 2-μm range. The technique is based on the frequency degenerate SPDC under Type II extended phase matching (EPM). We described the EPM characteristics of KN and showed that it is practically feasible for a 1064-nm pumped SPDC under moderate temperature conditions. The effective nonlinear optic coefficient of KN is at least four-times larger than those of other crystals using the Type II EPM approach, which implies a significant improvement in SPDC efficiency. The joint spectral analysis showed that a pair of photons can be generated with a high purity of 0.995 through proper pump filtering.
Summary form only given. Spontaneous degenerate parametric scattering [down-conversion] is a 3-photon process with one pump photon of frequency 2/spl omega/ and two output photons of frequency /spl omega/. An optical vortex is defined as a beam containing a phase singularity, i.e. the change of phase around the center of the beam equals 2 /spl pi/m; where the integer m is the topological charge. Our experimental results using a BaB/sub 2/O/sub 4/ crystal under type II phase matching conditions and numerical simulations suggest that the vortex in the pump beam is transformed into a speckle-like structure, effectively that structure is composed of randomly occurring vortex and Gaussian beams. The two down-converted output signals (signal and idler) appear as rings of orthogonal polarization and, therefore, can be easily distinguished.