Ionizing radiation hazards from the tight focusing of ultrashort laser pulses in ambient air
Bibliographic record
Abstract
Manipulating unconfined ultrashort pulsed laser beams is increasingly common in academic research laboratories. Normally, health risks associated with beam propagation and alignment can be mitigated using protective eyewear and following standard laser safety guidelines. A recent investigation [1] has uncovered an additional, unexpected health risk. While working with High Numerical Aperture (HNA) reflective optics in ambient air, it was demonstrated that the laser pulse intensity at the focus was sufficient to accelerate electrons to relativistic energies and generate high dose-rate ionizing radiation. Non-linear effects in these conditions usually distort the propagating wavefront and render difficult the proper focusing of the beam. We have shown this does not hold true when focusing the output of the ALLS 100Hz Mid-IR laser beamline (2.8 mJ, 12 fs pulse centered at 1800 nm) with a reflective optic having a Numerical Aperture (NA) close to 1. Using this configuration, a radiation dose of 100's of mGy per minute was measured at 50 cm from the focus in ambient air, which exceed public dose limits in a very short time. Non-negligible dose measurements have also been observed with longer pulse durations, shorter wavelengths and standard off-the-shelf tight focusing optics from traditional optical suppliers. In this specific case, when using HNA reflective optics with ultrashort pulsed laser beams, the Laser Safety Officer (LSO) should carefully assess the risk related to hazardous ionizing radiation emitted by the focused beam.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".