arXiv subjects

Anders Brusch

Publications and source records attributed to Anders Brusch.

9 recordsLinked to original sources

arXiv2026

Quantifying Effective Heterodyne Detection Efficiency with SI-Traceable Standards

Accurate calibration of coherent optical receivers is essential for reliable performance assessment in coherent communications, precision and quantum sensing, and continuous-variable quantum key distribution (CV-QKD), where the effective detection efficiency directly impacts channel parameter estimation. We present a methodology traceable to the International System of Units (SI) to determine the effective heterodyne detection efficiency of balanced receivers using shot-noise-referenced measurements. The protocol relies on two observables acquired with an electrical spectrum analyzer: the heterodyne beat-note power and the local oscillator shot-noise variance, with explicit treatment of the analyzer's equivalent noise bandwidth (ENBW). The photon flux in the signal path is referenced to SI units via calibrated radiometric standards. We first validate the protocol on a free-space receiver, demonstrating consistency with an independently constructed optical loss chain across a wide range of signal powers and under controlled, calibrated attenuation. Extending the same estimator to a fiber-coupled, polarization-maintaining balanced receiver confirms that the protocol is robust for practical coherent-receiver architectures and intermediate frequencies in the MHz range. These results establish a traceable, uncertainty-bounded framework for real-time receiver calibration, providing a practical route for CV-QKD and other coherent optical systems.

quant-ph↗

arXiv2018

Designing and experimental verification of a photoacoustic flow sensor using computational fluid dynamics

A photoacoustic (PA) sensor for fast and real-time gas sensing is demonstrated. The PA sensor is a standalone system controlled by a Field-Programmable Gate Array (FPGA). The PA cell has been designed for flow noise immunity using computational fluid dynamics (CFD) analysis. The aim of the CFD analysis was to investigate and minimize the influence of the gas distribution and the flow noise on the PA signal. PA measurements were conducted at different flow rates by exciting molecular C-H stretch vibrational bands of hexane (C$_6$H$_{14}$) and decane (C$_{10}$H$_{22}$) molecules in clean air at 2950 cm$^{-1}$ (3.38 $μ$m) with a custom made mid-infrared interband cascade laser (ICL). We observe a (1$σ$, standard deviation) sensitivity of 0.4 $\pm0.1$ ppb (nmol/mol) for hexane in clean air at flow rates up to 1.7 L/min, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 2.5$\times 10^{-9}$ W cm$^{-1}$ Hz$^{-1/2}$, demonstrating high sensitivity and fast real-time gas analysis. An Allan deviation analysis for decane shows that the detection limit at optimum integration time is 0.25 ppbV (nmol/mol).

physics.ins-det↗

arXiv2016

Photo-acoustic sensor for detection of oil contamination in compressed air systems

We demonstrate an online (in-situ) sensor for continuous detection of oil contamination in compressed air systems complying with the ISO-8573 standard. The sensor is based on the photo-acoustic (PA) effect. The online and real-time PA sensor system has the potential to benefit a wide range of users that require high purity compressed air. Among these are hospitals, pharmaceutical industries, electronics manufacturers, and clean room facilities. The sensor was tested for sensitivity, repeatability, robustness to molecular cross-interference, and stability of calibration. Explicit measurements of hexane (C${_6}$H$_{14}$) and decane (C${_{10}}$H$_{22}$) vapors via excitation of molecular C-H vibrations at approx. 2950 cm$^{-1}$ (3.38 $μ$m) were conducted with a custom made interband cascade laser (ICL). For the decane measurements a (1 $σ$) standard deviation (STD) of 0.3 ppb was demonstrated, which corresponds to a normalized noise equivalent absorption (NNEA) coefficient for the prototype PA sensor of 2.8$\times 10^{-9}$ W cm$^{-1}$ Hz$^{1/2}$.

physics.ins-det↗

arXiv2014

Phase-Sensitive Noise Suppression in a Photoacoustic Sensor based on Acoustic Circular Membrane Modes

A photoacoustic (PA) sensor based on higher order acoustic modes is demonstrated. The PA sensor is designed to enhance the gas-detection performance and simultaneously suppress ambient noise sources (e.g. flow noise, electrical noise and external acoustic noise). Two microphones are used and positioned such that the PA signals are ($π$) out of phase. Ambient acoustic noise are approximately in the same phase and will be subtracted and thus improve the SNR. In addition, by placing the gas in- and outlets so that the gas flows through the node of the first higher order membrane mode the coupling of flow noise is approximately 20 dB lower compared with flow through the fundamental mode at 5 L/min. The noise reduction and thus the increase in sensitivity is demonstrated by measuring vibrational lines of methanol and methane using a broadband interband cascade laser emitting radiation at 3.38 $μ$m. A signal-to-noise improvement of 20 (26 dB) using higher order modes are demonstrated compared with the fundamental mode. The maximum normalized noise equivalent absorption coefficient is 1.1 $\times 10^{-6}$ W cm$^{-1}$ Hz$^{1/2}$ for a flow of 5 L/min. It is anticipated that the noise cancelation strategy may find use in many practical industrial and environmental PA sensors, where ambient noise sources plays a crucial role for the absolute sensitive.

physics.optics↗

arXiv2014

A versatile integrating sphere based photoacoustic sensor for trace gas monitoring

A compact versatile photoacoustic (PA) sensor for trace gas detection is reported. The sensor is based on an integrating sphere as the PA absorption cell with an organ pipe tube attached to increase the sensitivity of the PA sensor. The versatility and enhancement of the sensitivity of the PA signal is investigated by monitoring specific ro-vibrational lines of CO2 in the 2 mm wavelength region and of NO2 in the 405 nm region. The measured enhancement factor of the PA signal exceeds 1200, which is due to the acoustic resonance of the tube and the absorption enhancement of the integrating sphere relatively to a non-resonant single pass cell. It is observed that the background absorption signals are highly attenuated due to the thermal conduction and diffusion effects in the polytetrafluoroethylene cell walls. This demonstrates that careful choice of cell wall materials can be highly beneficial to the sensitivity of the PA sensor. These properties makes the sensor suitable for various practical sensor applications in the ultraviolet to the near infrared wavelength region, including climate, environmental and industrial monitoring.

physics.optics↗

arXiv2009

Isotope shifts of the (3s3p)$^3$P$_{0,1,2}$ - (3s4s)$^3$S$_1$ Mg I transitions

We report measurements of the isotope shifts of the (3s3p)$^3$P$_{0,1,2}$ - (3s4s)$^3$S$_1$ Mg I transitions for the stable isotopes $^{24}$Mg (I=0), $^{25}$Mg (I=5/2) and $^{26}$Mg (I=0). Furthermore the $^{25}$Mg $^3$S$_1$ hyperfine coefficient A($^3$S$_1$) = (-321.6 $\pm$ 1.5) MHz is extracted and found to be in excellent agreement with state-of-the-art theoretical predictions giving A($^3$S$_1$) = -325 MHz and B($^3$S$_1$) $\simeq 10^{-5}$ MHz. Compared to previous measurements, the data presented in this work is improved up to a factor of ten.

physics.atom-ph↗

arXiv2006

An accurate optical lattice clock with 87Sr atoms

We report a frequency measurement of the 1S0-3P0 transition of 87Sr atoms in an optical lattice clock. The frequency is determined to be 429 228 004 229 879 (5) Hz with a fractional uncertainty that is comparable to state-of-the-art optical clocks with neutral atoms in free fall. Two previous measurements of this transition were found to disagree by about 2x10^{-13}, i.e. almost four times the combined error bar, instilling doubt on the potential of optical lattice clocks to perform at a high accuracy level. In perfect agreement with one of these two values, our measurement essentially dissipates this doubt.

physics.atom-ph↗

arXiv2005

Hyperpolarizability effects in a Sr optical lattice clock

We report the observation of the higher order frequency shift due to the trapping field in a $^{87}$Sr optical lattice clock. We show that at the magic wavelength of the lattice, where the first order term cancels, the higher order shift will not constitute a limitation to the fractional accuracy of the clock at a level of $10^{-18}$. This result is achieved by operating the clock at very high trapping intensity up to $400 $kW/cm$^2$ and by a specific study of the effect of the two two-photon transitions near the magic wavelength.

physics.atom-ph↗

arXiv2005

Accurate spectroscopy of Sr atoms

We report the frequency measurement with an accuracy in the 100 kHz range of several optical transitions of atomic Sr : $^1S_0- ^3P_1$ at 689 nm, $^3P_1- ^3S_1$ at 688 nm and $^3P_0- ^3S_1$ at 679 nm. Measurements are performed with a frequency chain based on a femtosecond laser referenced to primary frequency standards. They allowed the indirect determination with a 70 kHz uncertainty of the frequency of the doubly forbidden $5s^2^1S_0- 5s5p^3P_0$ transition of $^{87}$Sr at 698 nm and in a second step its direct observation. Frequency measurements are performed for $^{88}$Sr and $^{87}$Sr, allowing the determination of $^3P_0$, $^3P_1$ and $^3S_1$ isotope shifts, as well as the $^3S_1$ hyperfine constants.

physics.atom-ph↗