arXiv subjects

Szymon Wójtewicz

Publications and source records attributed to Szymon Wójtewicz.

5 recordsLinked to original sources

arXiv2026

Accounting for the detection response brings cavity ring-down spectroscopy to sub-permille accuracy

For nearly four decades, cavity ring-down spectroscopy (CRDS) has been among the simplest, most widely used absorption techniques, requiring no calibration because it measures decay times, not intensities. Yet as accuracy requirements have tightened, CRDS has proven strikingly inconsistent: reported errors range from several percent to the permille level - the signature of an uncontrolled systematic effect so far worked around rather than resolved. This has confined applications demanding the highest accuracy - from testing ab initio theory to atmospheric sensing and quantum-based metrology - to a handful of laboratories relying on advanced calibration or architectures, at the cost of simplicity. Here we show the main source was hiding in plain sight: the detection chain's transient response. It distorts every ring-down, biasing the retrieved decay times differently from instrument to instrument - a bias that routine truncation of the early decay masks rather than removes. We measure this response with a calibration-free beat-note method and build it into the ring-down model. Validation uses a well-characterized carbon monoxide transition and an independent frequency-based reference. Across four detection configurations, line-intensity biases of up to 14 % shrink 41- to 87-fold, the results converge, reaching up to sub-permille agreement with the reference. This holds down to 4 us ring-down times, extending accurate CRDS to stronger absorption. Independent of the absorbing species and requiring no change to the CRDS setup, the approach turns a technique valued for its simplicity into one equally valued for its accuracy. Benchmark-quality measurement thus comes within reach of any CRDS laboratory.

physics.optics↗

arXiv2025

Leveraging resonant frequencies of an optical cavity for spectroscopic measurement of gas temperature and concentration

We introduce a spectroscopic approach to primary gas thermometry, harnessing precise optical cavity resonance frequencies and ab initio molecular line intensity calculations. By utilizing CO (3-0) vibrational band lines and cavity mode dispersion spectroscopy, we achieve an uncertainty of 82 ppm (24 mK at 296 K) in line-intensity-ratio thermometry (LRT) - over an order of magnitude lower than any previously reported spectroscopic thermometry at gas pressures above 1.2 kPa. This method extends high-precision spectroscopic thermometry across a pressure range an order of magnitude larger than prior techniques, enabling a fully optical, non-contact, and molecule-selective primary amount-of-substance measurement. We further demonstrate sub-permille uncertainty in gas concentration measurements across pressures from 50 Pa to 20 kPa, significantly enhancing the precision and versatility of spectroscopic gas metrology.

physics.optics↗

arXiv2025

Cavity-enhanced spectroscopy in the deep cryogenic regime -- new hydrogen technologies for quantum sensing

Spectrometers based on high-finesse optical cavities have proven to be powerful tools for applied and fundamental studies. Extending this technology to the deep cryogenic regime is beneficial in many ways: Doppler broadening is reduced, peak absorption is enhanced, the Boltzmann distribution of rotational states is narrowed, all unwanted molecular species disturbing the spectra are frozen out, and dense spectra of complex polyatomic molecules become easier to assign. We demonstrate a cavity-enhanced spectrometer fully operating in the deep cryogenic regime down to 4 K. We solved several technological challenges that allowed us to uniformly cool not only the sample but also the entire cavity, including the mirrors and cavity length actuator, which ensures the thermodynamic equilibrium of a gas sample. Our technology well isolates the cavity from external noise and cryocooler vibrations. This instrument enables a variety of fundamental and practical applications. We demonstrate a few examples based on accurate spectroscopy of cryogenic hydrogen molecules: accurate test of the quantum electrodynamics for molecules; realization of the primary SI standards for temperature, concentration and pressure in the deep cryogenic regime; measurement of the H$_{2}$ phase diagram; and determination of the ortho-para spin isomer conversion rate.

physics.atom-ph↗

arXiv2024

Heterodyne dispersive cavity ring-down spectroscopy exploiting eigenmode frequencies for high-fidelity measurements

Measuring low light absorption with combined uncertainty < 1 permille is crucial in a wide range of applications. Popular cavity ring-down spectroscopy can provide ultra-high precision, below 0.01 permille, but its accuracy is strongly dependent on the measurement capabilities of the detection system and typically is about 10 permille. Here, we exploit the optical frequency information carried by the ring-down cavity electromagnetic field, not explored in conventional CRDS, for high-fidelity spectroscopy. Instead of measuring only the decaying light intensity, we perform heterodyne detection of ring-downs followed by Fourier analysis to provide exact frequencies of optical cavity modes and a dispersive spectrum of a gas sample from them. This approach is insensitive to inaccuracies in light intensity measurements and eliminates the problem of detector band nonlinearity, the main cause of measurement error in traditional CRDS. Using the CO and HD line intensities as examples, we demonstrate the sub-permille accuracy of our method, confirmed by the best ab initio results, and the long-term repeatability of our dispersion measurements at 10^(-4) level. Such results have not been achieved in optical spectroscopy before. The high accuracy of the presented method indicates its potential in atmospheric studies, isotope ratio metrology, thermometry, and the establishment of primary gas standards.

physics.optics↗

arXiv2018

Measurement of electron-calcium ionization integral cross section using an ion trap with a low-energy, pulsed electron gun

An apparatus for production of various atomic and molecular ions inside a linear Paul trap has been set up. The system applies a custom-made, low energy, pulsed electron gun to produce ions in electron impact process. Such ionization method can find some interesting possible applications such as derivation of ions inaccessible other-ways, which can be used in molecular ion experiments. The technique allows also for determination of cross sections for various collisional processes. As a feasibility study, the apparatus was used for determination of ionization integral cross section of calcium in the 16--160 eV range of electron impact energy. The obtained cross section values are discussed and compared with existing data sets.

physics.ins-det↗