Hanieh Fattahi

Energy consumption is on track to become a serious bottleneck in integrating quantum technologies with existing information and communication infrastructure. In photonic quantum technologies, a considerable portion of the energy overhead stems from the use of lasers, whose high coherence has long been considered indispensable for preparing quantum states of light. Here, we demonstrate that despite their low optical coherence, natural sources of light, such as sunlight, can produce quantum-entangled photon states by means of nonlinear optical effects. From spontaneous parametric down-conversion pumped by sunlight, we detect polarization-entangled photon pairs with a concurrence of C =0.905±0.053, a purity of P =0.919±0.045, and a fidelity to a Bell state of F =0.939±0.027. The resulting two-photon state violates Bell’s inequality with S =2.5408±0.2171, which exceeds the threshold value of 2 to confirm quantum behavior. More importantly, we observe a photon pair generation rate of ∼1600s ⁻¹ ( mW of pump power ) ⁻¹ , which is comparable to that of the laser-pumped SPDC when normalized for the spectral bandwidth of the pump. Our work paves the way for developing sustainable and accessible photonic quantum technologies, especially for implementation in resource-constrained areas such as the Arctic region and satellites in space for interplanetary missions.

Solar-pumped lasers, predominantly based on neodymium gain media, offer a promising route to renewable laser-energy conversion and space-based photonics; however, their performance has been constrained by thermal loading and limited power scalability. Here, we propose and numerically investigate a solar-pumped ytterbium thin-disk gain medium in combination with a dome concentrator that enables multipass solar pumping and enhanced absorption. The design yields comparably low lasing thresholds for neodymium- and ytterbium-doped media, while ytterbium provides superior power scalability, enabling up to threefold higher output power. We further identify ytterbium-doped medium combined with a spherical concentrator as a viable solar-pumped, radiation-balanced configuration, achieving self-cooled lasing at solar pump intensities of 28.5 kW cm-2 within the 1020-1033 nm window of the solar spectrum. The spherical concentrator increases the averaged fluence of the solar pump while permitting anti-Stokes fluorescence to escape efficiently. These results establish multi-pass, solar-pumped thin-disk ytterbium lasers as a compact, scalable, and sustainable platform for high-performance solar-pumped lasers

We demonstrate stimulated Raman fieldoscopy for label-free detection of neurotransmitters dissolved in water. Broadband stimulated Raman scattering and short-wavelength infrared absorption are recorded simultaneously by directly measuring the electric field of light after the sample with attosecond precision. The amplitude and phase-resolved measurement captures distinct complementary vibrational features, establishing a proof of principle for sensitive biochemical analysis in an aqueous environment.

Accessing the electric field of light with petahertz bandwidths in ambient air is a rapidly advancing frontier, essential for probing ultrafast dynamics driven by classical or quantum ultrashort pulses. Near-petahertz fieldoscopy has recently demonstrated sub-cycle access to light-matter interactions, enabling label-free spectro-microscopy of liquids and solids with unprecedented spatiotemporal resolution, detection sensitivity, and dynamic range. However, current implementations still rely on temporal scanning and averaging over many laser pulses. Here, we introduce photonic time-stretch fieldoscopy, enabling single-shot electric-field detection at near-petahertz frequencies. Numerical results demonstrate that integrating fieldoscopy with a nonlinear time lens enables the real-time acquisition of ultrashort optical waveforms with a detection bandwidth approaching petahertz. The resulting large temporal aperture and attosecond resolution allow direct single-shot detection of transient electric fields generated in solid or liquid samples. This concept opens new avenues for petahertz electronics, ultrafast spectro-microscopy, and the study of dynamic, non-repetitive optical phenomena

Scalable, high‐speed, small‐footprint photonic switching platforms are essential for advancing optical communication. An effective optical switch must operate at high duty cycles with fast recovery times, while maintaining substantial modulation depth and full reversibility. Colloidal nanocrystals, such as indium tin oxide (ITO), offer a scalable platform to meet these requirements. In this work, the transmission of ITO nanocrystals near their epsilon‐near‐zero wavelength is modulated by two‐cycle optical pulses at a repetition rate of one megahertz. The modulator exhibits a broad bandwidth spanning from 2 to 2.5 µm. Sensitive fieldoscopy measurements resolve the transient electric‐field response of the ITO for the first time, showing that the modulation remains reversible for excitation fluences up to 1.2 mJ cm ⁻² with a modulation depth of 10%, and becomes fully irreversible beyond 3.3 mJ cm ⁻² , while reaching modulation depth of up to 20%. Field sampling further indicates that at higher excitation fluences, the relative contribution from the first cycle of the optical pulses is reduced. These findings are crucial for the development of all‐optical switching, telecommunications, and sensing technologies capable of operating at terahertz switching frequencies.

EPJ Web of Conferences, open-access proceedings in physics and astronomy

Scalable, high-speed, small-footprint photonic switching platforms are essential for advancing optical communication. An effective optical switch must operate at high duty cycles with fast recovery times, while maintaining substantial modulation depth and full reversibility. Colloidal nanocrystals, such as indium tin oxide (ITO), offer a scalable platform to meet these requirements. In this work, the transmission of ITO nanocrystals near their epsilon-near-zero wavelength is modulated by two-cycle optical pulses at a repetition rate of one megahertz. The modulator exhibits a broad bandwidth spanning from 2 um to 2.5 um. Sensitive fieldoscopy measurements resolve the transient electric-field response of the ITO for the first time, showing that the modulation remains reversible for excitation fluences up to 1.2 mJ/cm2 with a modulation depth of 10%, and becomes fully irreversible beyond 3.3 mJ/cm2, while reaching modulation depth of up to 20%. Field sampling further indicates that at higher excitation fluences, the relative contribution from the first cycle of the optical pulses is reduced. These findings are crucial for the development of all-optical switching, telecommunications, and sensing technologies capable of operating at terahertz switching frequencies.

Gas-filled hollow core fibers allow the generation of single-cycle pulses at megahertz repetition rates. When coupled with difference frequency generation, they can be an ideal driver for generating carrier-envelope phase stable, octave-spanning pulses in the short-wavelength infrared. In this work, we investigate the dependence of the polarization state in gas-filled hollow-core fibers (HCF) on the subsequent difference frequency generation stage. We show that by adjusting the input polarization state of light in geometrically symmetric systems, such as hollow-core fibers, one can achieve precise control over the polarization state of the output pulses. This manipulation preserves the temporal characteristics of the generated ultrashort pulses, especially when operating at a near single-cycle regime. We leverage this property to boost the downconversion efficiency of the near single-cycle pulses in a type I difference frequency generation stage. Our technique overcomes the bandwidth and dispersion constraints of the previous methods that rely on broadband waveplates or adjustment of crystal axes relative to the laboratory frame. This advancement is crucial for experiments demanding pure polarization states in the eigenmodes of the laboratory frame.