dewitt_2001 =========== M\. J\. DeWitt, E\. Wells and R\. R\. Jones, "Ratiometric Comparison of Intense Field Ionization of Atoms and Diatomic Molecules", Phys\. Rev\. Lett\. 87, 153001 \(2001\) `Source record `__ · :doc:`Catalogue ` · :doc:`Review register ` DOI: `10\.1103/PhysRevLett\.87\.153001 `__ **Source kind:** measurement **Recorded technique:** Simultaneous ion\-yield measurement in mixed atomic and molecular targets \(p\. 2\)\: 'low density gas targets are exposed to a focused laser beam in a high vacuum chamber with a base pressure of approximately 5 x 10^\-10 torr\. Single ion events are gathered via time\-of\-flight \(TOF\) mass spectrometry with a chevron microchannel plate \(MCP\) detector, and recorded with a multichannel scaler \(MCS\) that is capable of counting multiple events per trigger', with sample pressures set for 'a count rate of less than one event per trigger in any ion channel'\. The atom and the molecule are introduced through separate leak valves \(the Ar\:N2 pair also as a prepared mixture, 0\.042\:0\.067\:1 Ar\:N2\:He, whose RGA ratio 'agreed with the known ratio in the prepared mix to within 4%'\); partial pressures from a residual gas analyser 'corrected for electron impact ionization cross section'\. Each yield is divided by the number of shots and the partial pressure \('counts/\(shot torr\)'\), and the molecular yield by the atomic one\. Laser \(p\. 2\)\: 'Intense, 2 mJ, 790 nm, 100 fs laser pulses \.\.\. amplified Ti\:sapphire laser operating at a 1 kHz repetition rate', focused by a 30 cm lens or a 5 cm gold mirror; the ratio 'is insensitive to the specific focusing optic used and to the precise position of the laser focus'\. 10^5 to 10^7 shots per intensity\. The polarisation is not stated\. **Materials in structured entries:** N2, O2 **Dataset quantities:** ionization\_yield\_ratio **Contents:** 4 datasets; 0 formulas. Curation notes -------------- PRL 87, 153001 \(4 pp\.\), PDF pages 1\-4 = 153001\-1 to \-4\. Identity checked on PDF p\. 1 on 2026\-10\-01\: 'Ratiometric Comparison of Intense Field Ionization of Atoms and Diatomic Molecules', Merrick J\. DeWitt, E\. Wells and R\. R\. Jones, University of Virginia; 'VOLUME 87, NUMBER 15 \.\.\. 8 OCTOBER 2001'; '\(Received 3 May 2001; published 21 September 2001\)'\. WHAT THE RATIO IS\. The molecular yield over the companion atom's, both counted in the same mixture at the same shots \(O2\:Xe, Fig\. 1; N2\:Ar, Fig\. 2\)\. It is a total\-ionisation ratio, not strictly singly charged ions\: 'While single ionization is by far the dominant process observed, at the highest intensities, double and dissociative ionization cannot be neglected \.\.\. In most cases, the dissociative and double ionization yields are simply added to the single ionization channel' \(p\. 2\)\. DETECTION EFFICIENCY \(detection\_correction = "none"\)\. 'Uniform detection efficiency of all ions is ensured by accelerating them to greater than 4 kV before impacting the detector, and by reducing the lower MCS discriminator to a level where the measured Xe2\+\:Xe\+ ratio is found to be independent of the discriminator setting\. Thus, ionization events from different species are detected with identical efficiencies' \(p\. 2\)\. Ref\. 19 \(p\. 4\)\: 'In their data analysis, Guo et al\. \[10\] applied a mass\-dependent detection efficiency correction to their ion yields that effectively reduced their O2\:Xe ionization ratio by a factor of 2\. We do not believe that this correction is necessary for digital measurements from MCP detectors and, therefore, we have not included it in our results\. Accordingly, we present the data of Guo et al\. without the adjustment as well\.' A ratio corrected by a mass\-dependent efficiency \(as dura\_2012's Z/sqrt\(M\)\) is therefore not comparable with these without that factor\. INTENSITY\. 'The absolute ionizing intensities are determined by the onset of double ionization for the noble gases \[10\]' \(p\. 2; ref\. 10, Guo et al\., Phys\. Rev\. A 58, R4271 \(1998\)\)\. No uncertainty of the intensity is stated\. The text shows how steep the ratio is in it\: 'shifting the intensity scale of our N2\+ data by 10% changes the N2\:Ar ionization ratio at 1 x 10^14 W cm^\-2 from 1\.90 to 0\.93' \(p\. 1\)\: this is why the ratios are measured in mixtures\. UNCERTAINTY\. 'the primary sources of error in our determinations are due to statistics and the uncertainty in the partial pressure determination \(~5%\), not from double ionization or fragmentation processes' \(p\. 2; '~' read on the page image\)\. The bars' level is not stated\. Fig\. 1's legend\: 'Errors smaller than symbol size not shown'\: of the 18 O2 points only the lowest has bars; for the others the bar's half\-length is under the marker's half\-height, 1\.84 pt, 0\.034 in the ratio\. WAVELENGTH\. 790 nm \(p\. 2 and both legends\); the N2\:Ar paragraph says 'for 100 fsec 780 nm pulses' \(p\. 3\), taken as a slip for the 790 nm of the legend\. EXTRACTED \(2026\-10\-01\) by tools/extract/dewitt\_2001\.py from the vector drawings of Figs\. 1 and 2 \(p\. 3\), whose docstring describes the reading\: the axes from the frame's tick segments matched to the text layer's labels \(log intensity, linear ratio; every tick within 0\.057 pt of the fitted scales\: the drawing's coordinates are quantised to about 0\.1 pt\), the markers' centres and the bars' ends\. Guo et al\.'s points \(open circles in Fig\. 1, open triangles in Fig\. 2\), the S2 and F2 points are not taken\. CHECKS\. \(1\) The text\: the O2\:Xe ratio 'At low intensities \.\.\. remains nearly constant at a value between 0\.15 and 0\.2 times that of Xe\. Above 10^14 W cm^\-2, saturation of the Xe yield results in an increase of the ionization ratio' \(p\. 2\)\: the 18 points \(1\.90e13 to 9\.46e13 W/cm2\) have a median of 0\.183 and span 0\.136\-0\.243, rising above 0\.21 only at the last two \(9\.0 and 9\.5e13\); 'Above 5 x 10^14 W cm^\-2 both species ionize with near 100% efficiency and the ratio saturates at unity' refers to intensities beyond this work's O2 points \(the figure's points there are Guo et al\.'s\)\. The N2\:Ar ratio 'is nearly constant at approximately 1\.7, before falling towards unity near the saturation intensity' \(p\. 3\)\: the 34 points' median is 1\.82 \(1\.52\-2\.03 below 4e14 W/cm2\), falling to 1\.05 at 6\.1e14\. The N2\:Ar ratio 'at 1 x 10^14 W cm^\-2' is printed 1\.90 \(p\. 1\)\: interpolated between the points at 9\.88e13 and 1\.07e14 W/cm2 it is 1\.945 \(2\.4 % above; the bars there are \+\-0\.18\)\. \(2\) Loriot et al\. 2008 \(loriot\_2008, Fig\. 7\) redraw ten of these N2\:Ar points \('DeWitt et al \[35\] \(790 nm, 100 fs\)', 44 to 99 TW/cm2\)\: tools/extract/loriot\_2008\.py compares them with these\: all ten match within 0\.21 % in intensity and 0\.005 in the ratio\. \(3\) The extracted points drawn on the rendered page and inspected on 2026\-10\-01\: every O2 and N2 square captured once, none of Guo et al\.'s, the S2 or F2 markers, the legends' markers excluded, the bars' ends on the caps\. \(4\) The N2 bars are symmetric about their markers within 0\.114 pt \(0\.0025 in the ratio\)\. **Recorded bibliographic identity status:** VALIDATED. This concerns identification of the source; it does not establish the scientific correctness of its contents. Datasets -------- dewitt\_2001/fig1\_O2\_Xe ~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "fig1_O2_Xe", "material": "O2", "file": "O2/dewitt_2001__fig1_O2_Xe.csv", "table": "fig_4f3a1feb7459", "digitised": "vector", "quantity": "ionization_yield_ratio", "unit": "1", "abscissa": "intensity", "abscissa_unit": "W/cm2", "use": "check", "uncertainty": { "column": true, "absolute": 0.002, "level": "not stated" }, "parameters": { "companion": "Xe", "wavelength_nm": 790, "pulse_fs": 100, "pulse_fs_definition": "as printed ('790 nm, 100 fs'); the measure is not stated", "polarization": "not stated", "detection_correction": "none", "detection_correction_note": "uniform MCP detection asserted (ions accelerated to over 4 kV, discriminator set so Xe2+:Xe+ is independent of it); Guo et al.'s mass-dependent correction 'effectively reduced their O2:Xe ionization ratio by a factor of 2' and is not applied (ref. 19)", "intensity_calibration": "the onset of double ionisation of the noble gases (after Guo et al. 1998); no uncertainty stated", "mixture": true } } Fig\. 1, p\. 3, 'O2\: 790 nm, 100 fs' \(open squares\)\: the O2\+\:Xe\+ yield ratio in the same mixture \(O2 including its dissociative and double ionisation, the record's notes\) against the peak intensity, 18 points, 1\.90e13\-9\.46e13 W/cm2, ratio 0\.136\-0\.243, read from the vector drawing\. Two points share 5\.20e13 W/cm2 \(0\.155 and 0\.185\)\. sigma\: half the bar, drawn only on the lowest point \(\+\-0\.084\); for the others 'Errors smaller than symbol size not shown' \(the legend\), under 0\.034\. No detector\-efficiency correction \(the record's notes, ref\. 19\)\. Intensities from 'the onset of double ionization for the noble gases', no uncertainty stated\. 0\.002\: the digitising \(the drawing's 0\.06 pt against 26\.7 pt per 0\.5\); the intensity to 0\.1 %\. dewitt\_2001/fig2\_N2\_Ar ~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "fig2_N2_Ar", "material": "N2", "file": "N2/dewitt_2001__fig2_N2_Ar.csv", "table": "fig_9c453cfd77c2", "digitised": "vector", "quantity": "ionization_yield_ratio", "unit": "1", "abscissa": "intensity", "abscissa_unit": "W/cm2", "use": "check", "uncertainty": { "column": true, "absolute": 0.002, "level": "not stated" }, "parameters": { "companion": "Ar", "wavelength_nm": 790, "pulse_fs": 100, "pulse_fs_definition": "as printed ('790 nm, 100 fs'; '100 fsec 780 nm pulses' in the text, p. 3); the measure is not stated", "polarization": "not stated", "detection_correction": "none", "detection_correction_note": "uniform MCP detection asserted (ions accelerated to over 4 kV, discriminator set so Xe2+:Xe+ is independent of it); no mass-dependent correction (ref. 19)", "intensity_calibration": "the onset of double ionisation of the noble gases (after Guo et al. 1998); no uncertainty stated", "mixture": true } } Fig\. 2, p\. 3, 'N2\: 790 nm, 100 fs' \(open squares\)\: the N2\+\:Ar\+ yield ratio in the same mixture \(including dissociative and double ionisation, the record's notes\) against the peak intensity, 34 points, 4\.35e13\-6\.13e14 W/cm2, ratio 1\.049\-2\.032, read from the vector drawing\. sigma\: half the bar \(0\.088\-0\.382; the bars symmetric within 0\.0025\), level not stated\. No detector\-efficiency correction \(the record's notes\)\. The text\: 'nearly constant at approximately 1\.7, before falling towards unity near the saturation intensity' \(p\. 3; the points' median 1\.82\) and 1\.90 at 1e14 W/cm2 \(p\. 1; the points give 1\.945\)\. Intensities from 'the onset of double ionization for the noble gases', no uncertainty stated\. 0\.002\: the digitising \(0\.06 pt against 22\.6 pt per 0\.5\); the intensity to 0\.1 %\. dewitt\_2001/text\_O2\_Xe\_low\_intensity ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "text_O2_Xe_low_intensity", "material": "O2", "table": "text", "quantity": "ionization_yield_ratio", "unit": "1", "abscissa": "label", "use": "check", "uncertainty": { "column": true, "level": "bound" }, "parameters": { "companion": "Xe", "wavelength_nm": 790, "pulse_fs": 100, "polarization": "not stated", "detection_correction": "none", "intensity_range": "'At low intensities', below 1e14 W/cm2 (the saturation of Xe above it); Fig. 1's O2 points 1.9e13-9.5e13 W/cm2", "mixture": true } } 1 inline points in the source record. p\. 2\: 'At low intensities, the total ion yield of O2\+ remains nearly constant at a value between 0\.15 and 0\.2 times that of Xe\. Above 10^14 W cm^\-2, saturation of the Xe yield results in an increase of the ionization ratio\.' The printed interval 0\.15\-0\.2 is recorded as its centre and half\-width, 0\.175 \+\- 0\.025 with level 'bound' \(a value somewhere in the interval\); the interval, not the 0\.175, is what is printed\. 'Low intensities'\: below 1e14 W/cm2 by the next sentence; Fig\. 1's O2 points start at 1\.9e13\. 'Total ion yield'\: dissociative and double ionisation added \(the record's notes\)\. No detector\-efficiency correction\. dewitt\_2001/text\_N2\_Ar\_plateau ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "text_N2_Ar_plateau", "material": "N2", "table": "text", "quantity": "ionization_yield_ratio", "unit": "1", "abscissa": "label", "use": "check", "parameters": { "companion": "Ar", "wavelength_nm": 790, "pulse_fs": 100, "polarization": "not stated", "detection_correction": "none", "intensity_range": "not stated with the number; the plateau of Fig. 2, about 4.4e13 to 4e14 W/cm2, before the fall 'towards unity near the saturation intensity'", "mixture": true } } 1 inline points in the source record. p\. 3\: 'Our ratiometric determinations indicate that the N2\:Ar ratio for 100 fsec 780 nm pulses is nearly constant at approximately 1\.7, before falling towards unity near the saturation intensity', and p\. 2\: 'N2\:Ar ~ 0\.7 \[10\], 0\.2 \[16\], 1 \[20\], 1\.7 \[our results\]' with the pulse durations '30 fs \[10\], 200 fs \[16\], 50 fs \[20\], and 100 fs \[our results\]'\. No uncertainty or intensity range is printed with the number; Fig\. 2 shows the plateau from 4\.4e13 to about 4e14 W/cm2 \(the points' median 1\.82\)\. The wavelength\: 790 nm by the legend \(the text's 780 nm, the record's notes\)\. No detector\-efficiency correction\. Formulas -------- No formulas are recorded. Corrections ----------- No dataset errata are recorded in this source record. Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register ` for the checks and decisions.