arXiv subjects

Frank Kühnemann

Publications and source records attributed to Frank Kühnemann.

6 recordsLinked to original sources

arXiv2026

Generation of continuous-wave laser light at 148.4 nm using cavity-enhanced second harmonic generation in $BaMgF_4$

The development of a nuclear optical clock based on \textsuperscript{229}Th is expected to influence the next generation of time and frequency standards. At its heart is the need for a continuous wave (CW) at laser at 148.4~nm to drive the clock transition between the ground and excited isomeric state. In this work we experimentally investigate the potential of BaMgF\textsubscript{4} crystals to create a CW solid state laser at the vacuum ultraviolet (VUV) wavelength of 148.4~nm via cavity-enhanced second harmonic generation. For this purpose, a BaMgF\textsubscript{4} crystal was grown, optically polished and periodically poled. The crystal was inserted into a power-enhancement cavity, resonant at the fundamental wavelength of 296.8~nm and the generated laser light at 148.4~nm was characterized. Within this proof-of-concept investigation, a VUV output power of typically ($16\pm1$)~pW is obtained. This marks the first time that this type of crystal is used to generate VUV laser light. The experimental findings are compared to theoretical expectations and provide a clear path for future improvements, which could have implications not only for compact laser sources in the VUV but also solid-state as well as single-ion based \textsuperscript{229}Th nuclear clocks.

physics.optics↗

arXiv2025

Mid-IR hyperspectral imaging with undetected photons

Sensing with undetected photons has become a vibrant, application-driven research domain with a special focus on the mid-infrared (mid-IR) wavelength region. Since the mid-IR contains spectral bands with highly specific and strong molecular absorbance signatures, often referred to as fingerprints, a multitude of different samples and their compositions can be detected and quantified spectroscopically. Enhancing this inherently sample alteration-free spectroscopic method with imaging capabilities leads to a powerful technique for environmental monitoring and biomedical applications that enables automated diagnostics while omitting time-consuming and non-reversible labeling steps. To evade the shortcomings of state-of-the-art instruments for mid-IR hyperspectral microscopy related to cost, complexity, power-consumption, and performance, which are associated with technological challenges for mid-IR cameras and low-noise and broadband mid-IR sources, here, we construct a proof-of-concept nonlinear interferometer in a wide-field imaging arrangement combined with high-resolution spectral acquisition by pixelwise quantum Fourier transform infrared spectroscopy. For the broadband range of 2300-3100 cm$^{-1}$, covering the important CH-stretch band, we perform hyperspectral imaging that simultaneously resolves 3500 spatial modes, each with a spectral resolution of 10 cm$^{-1}$ leveraging in total around 10$^5$ spatio-spectrally entangled photon modes. Our image acquisition uses a commercial, megapixel sCMOS camera, while a medium-power and compact c.w. pump laser is the only necessary light source.

physics.optics↗

arXiv2022

High-sensitivity quantum sensing with pump-enhanced spontaneous parametric down-conversion

Recent years have seen the development of quantum sensing concepts utilizing nonlinear interferometers based on correlated photon pairs generated by spontaneous parametric down-conversion (SPDC). Using SPDC far from frequency degeneracy allows a 'division of labor' between the mid-infrared photon for strongest sample interaction and the correlated near-infrared photon for low-noise detection. The small number of photons provided by SPDC and the resulting inferior signal-to-noise ratio are, however, a limiting factor preventing wide applicability of the novel sensing concept. Here, we demonstrate a nonlinear interferometer based on pump-enhanced SPDC with strongly improved emission rates, but maintaining broadband, spontaneous emission. For validation of the concept, we demonstrate high-resolution mid-infrared spectroscopy with near-infrared detection, showcasing the improved accuracy. Although the number of mid-infrared photons is about five orders of magnitude smaller than in classical spectrometers, the sensitivity of the quantum spectrometer becomes comparable, marking an essential step toward real-world applications.

quant-ph↗

arXiv2021

Tunable dual-comb spectrometer for mid-infrared trace gas analysis from 3 to 4.7 μm

Dual-frequency comb spectroscopy has emerged as a disruptive technique for measuring wide-spanning spectra with high resolution, yielding a particularly powerful technique for sensitive multi-component gas analysis. We present a spectrometer system based on dual electro-optical combs with subsequent conversion to the mid-infrared via tunable difference frequency generation, operating in the range from 3 to 4.7 $μ$m. The simultaneously recorded bandwidth is up to 454(1) GHz and a signal-to-noise ratio of 7.3(2) x 10$^2$ Hz$^{-1/2}$ can be reached. The conversion preserves the coherence of the dual-comb within 3 s measurement time. Concentration measurements of 5 ppm methane at 3.3 $μ$m, 100 ppm nitrous oxide at 3.9 $μ$m and a mixture of 15 ppm carbon monoxide and 5 % carbon dioxide at 4.5 $μ$m are presented with a relative precision of 1.4 % in average after 2 s measurement time. The noise-equivalent absorbance is determined to be less than 4.6(2) x 10$^{-3}$ Hz$^{-1/2}$.

physics.optics↗

arXiv2021

Nonlinear interferometer for Fourier-transform mid-infrared gas spectroscopy using near-infrared detection

Nonlinear interferometers allow for mid-infrared spectroscopy with near-infrared detection using correlated photons. Previous implementations have demonstrated a spectral resolution limited by spectrally selective detection. In our work, we demonstrate mid-infrared transmission spectroscopy in a nonlinear interferometer using single-pixel near-infrared detection and Fourier-transform analysis. A sub-wavenumber spectral resolution allows for rotational-line-resolving spectroscopy of gaseous samples in a spectral bandwidth of over 700$\,$cm$^{-1}$. We use methane transmission spectra around 3.3$\,μ$m wavelength to characterize the spectral resolution, noise limitations and transmission accuracy of our device. The combination of nonlinear interferometry and Fourier-transform analysis paves the way towards performant and efficient mid-infrared spectroscopy with near-infrared detection.

physics.optics↗

arXiv2020

Fourier transform infrared spectroscopy with visible light

Nonlinear interferometers allow spectroscopy in the mid-infrared range by detecting correlated visible light, for which non-cooled detectors with higher specific detectivity and lower dark count rates are available. We present a new approach for the registration of spectral information, which combines a nonlinear interferometer using non-degenerate spontaneous parametric down-conversion (SPDC) with a Fourier-transform spectroscopy concept. In order to increase the spectral coverage, we use broadband non-collinear SPDC in periodically poled LiNbO$_3$. Without the need for spectrally selective detection, continuous spectra with a spectral bandwidth of more than 100$\,$cm$^{-1}$ are achieved. We demonstrate transmission spectra of a polypropylene sample measured with ~ 6$\,$cm$^{-1}$ resolution in the spectral range between 3.2$\,μ$m to 3.9$\,μ$m.

physics.optics↗