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Characterization and elimination of thermomechanical effects in interferometric length measurement
Řeřucha, Šimon ; Holá, Miroslava ; Lazar, Josef ; Mikel, Břetislav ; Číp, Ondřej
Continuous efforts to develop dimensional measurements at both the nano- and macro-scale continue to present challenges in extending high-precision measurement procedures from the well-controlled experimental environment of a typically single measurement cycle to a constant-load production environment. In the field of laser interferometry, which is both a cornerstone of length metrology in general and an essential part of nanometrology, we have focused on long-term measurement stability (so-called zero-drift) in measurement scenarios and applications based on (mostly laser) interferometry. A well-characterized and compensated measurement zero-drift in such applications becomes more important both with applications in less controlled environments and with increasing measurement timeframes, such as long scans in microscopic nanometrology, long exposures in electron lithography, or interferometric reference calibrations with a larger number of calibration points or repetitions. The goal of the current research effort is to comprehensively investigate error effects and contributions to measurement uncertainty related to zero-drift in laser interferometry-based applications, with a particular focus on temperature effects (as these typically appear to be the dominant contribution) and approaches to suppress them. This effort involves several complementary directions.
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System for scanning hydrogen cyanide absorption lines
Hošek, Martin ; Řeřucha, Šimon ; Hrabina, Jan ; Čížek, Martin ; Pravdová, Lenka ; Číp, Ondřej
The definition of both meter and second relies on precisely measured frequency. The convenient sources of such frequencies are lasers stabilized by molecular vapours. The He-Ne lasers stabilized by iodin vapours represent the cornerstone sources in the visible spectrum. On the other hand, the infrared spectrum (particularly the 1550 nm C-band) is of metrological interest thanks to its cost-effective, readily available components. The widely used absorption media at 1550 nm has been two acetylene isotopes (12C2H2, 13C2H2), while H13C14N represents an alternative covering a wider spectrum well corresponding to the telecommunication C-band. The 2ν3 rotational-vibrational band had been investigated, but due to the use of not-so-precise methods, the presented data feature high uncertainty compared to acetylene data. We represent methods that will lead to precise assessments of hydrogen cyanide's absorption line centres with the potential to introduce HCN to Mise en Pratique, making it an internationally recognized source of precise frequency for the realization of traceable laser etalons.
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