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Conference on Lasers and Electro-Optics

The Transition from Linear to Quadratic Flux Scaling in Nonlinear Optical Processes with Variable Brightness Broadband Squeezed Vacuum

Tiemo S. Landes, Sofiane Merkouche, Markus Allgaier, Brian J. Smith, Michael G. Raymer

Published Jan 1, 2022• 0 citations
Publisher

Abstract

We characterize broadband parametric down conversion at low and high gain regimes. Two-photon absorption is measured at high gain, and sum-frequency generation is used to investigate the transition to high gain, and spectrally resolve two-photon interactions.
DOI
10.1364/cleo_qels.2022.fm3b.2

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Summary form only given. Recent advances in the design of broadband parametric down-conversion (PDC) sources have opened the possibility to attain a regime of high squeezing previously unacessible in the pulsed domain [1]. However, characterising a PDC source is a challenging task when multiple spectral modes are being squeezed simultaneously and one wants to determine the number of squeezers and their relative strengths. Moreover, as one approaches the high squeezing regime, a number of nonlinear effects that are not usually considered when the source is operated at low pump power become relevant [2, 3].Here we present a technique to perform a complete and self-referenced characterisation of a broadband PDC source using only classical measurements. Often, PDC sources are described by their joint spectral amplitude, which conveys the frequency correlations between the generated photons. Our method complements the information contained in the joint spectrum with a measurement of a second-order process that to our knowledge has not been directly measured until now. Generally, a PDC process can be described as a Bogoliuvov transformation of the bosonic operators of the formaouts (ω) = f dω'Us,s(ω,ω') ains + f dω''Us,i(ω,ω'')(ain i (ω''))† for the signal and analogously for the idler mode. In our work we show that these transfer functions, Us,s(i,i) and Us,i(i,s), can be measured in the stimulated regime [4,5], by scanning the wavelength of a narrowband seed laser and performing a frequency resolved intensity measurement of the generated light.
When two-photon interactions are induced by down-converted light with a bandwidth that exceeds the pump bandwidth, they can obtain a behavior that is pulselike temporally, yet spectrally narrow. At low photon fluxes this behavior reflects the time and energy entanglement between the down-converted photons. However, two-photon interactions such as two-photon absorption (TPA) and sum-frequency generation (SFG) can exhibit such a behavior even at high power levels, as long as the final state (i.e., the atomic level in TPA, or the generated light in SFG) is narrow-band enough. This behavior does not depend on the squeezing properties of the light, is insensitive to linear losses, and has potential applications. In this paper we describe analytically this behavior for traveling-wave down conversion with continuous or pulsed pumping, both for high- and low-power regimes. For this we derive a quantum-mechanical expression for the down-converted amplitude generated by an arbitrary pump, and formulate operators that represent various two-photon interactions induced by broadband light. This model is in excellent agreement with experimental results of TPA and SFG with high-power down-converted light and with entangled photons [Dayan et al., Phys. Rev. Lett. 93, 023005 (2004); 94, 043602 (2005); Pe'er et al., ibid. 94, 073601 (2005)].
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We report the experimental demonstration of coherent control with high power, broadband squeezed vacuum. Although incoherent and exhibiting the statistics of a thermal noise, broadband squeezed vacuum is shown to induce certain two-photon interactions as a coherent ultrashort pulse with the same spectral bandwidth. Utilizing pulse-shaping techniques we coherently control the sum-frequency generation of broadband squeezed vacuum over a range of two orders of magnitude. Coherent control of two-photon interactions with broadband squeezed vacuum can potentially obtain spectral resolutions and extinction ratios that are practically unattainable with coherent pulses.