| 1. |
- Axner, Ove, 1957-, et al.
(författare)
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Noise-immune cavity-enhanced analytical atomic spectrometry — NICE-AAS : a technique for detection of elements down to zeptogram amounts
- 2014
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Ingår i: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier. - 0584-8547 .- 1873-3565. ; 100, s. 211-235
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Tidskriftsartikel (refereegranskat)abstract
- Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is a powerful technique for detection of molecular compounds in gas phase that is based on a combination of two important concepts: frequency modulation spectroscopy (FMS) for reduction of noise, and cavity enhancement, for prolongation of the interaction length between the light and the sample. Due to its unique properties, it has demonstrated unparalleled detection sensitivity when it comes to detection of molecular constituents in the gas phase. However, despite these, it has so far not been used for detection of atoms, i.e. for elemental analysis. The present work presents an assessment of the expected performance of Doppler-broadened (Db) NICE-OHMS for analytical atomic spectrometry, then referred to as noise-immune cavity-enhanced analytical atomic spectrometry (NICE-AAS). After a description of the basic principles of Db-NICE-OHMS, the modulation and detection conditions for optimum performance are identified. Based on a previous demonstrated detection sensitivity of Db-NICE-OHMS of 5×10−12 cm−1 Hz−1∕2 (corresponding to a single-pass absorbance of 7×10−11 over 10 s), the expected limits of detection (LODs) of Hg and Na by NICE-AAS are estimated. Hg is assumed to be detected in gas phase directly while Na is considered to be atomized in a graphite furnace (GF) prior to detection. It is shown that in the absence of spectral interferences, contaminated sample compartments, and optical saturation, it should be feasible to detect Hg down to 10 zg/cm3 (10 fg/m3 or 10-5 ng/m3), which corresponds to 25 atoms/cm3, and Na down to 0.5 zg (zg = zeptogram = 10-21 g), representing 50 zg/mL (parts-per-sextillion, pps, 1:1021) in liquid solution (assuming a sample of 10 µL) or solely 15 atoms injected into the GF, respectively. These LODs are several orders of magnitude lower (better) than any previous laser-based absorption technique previously has demonstrated under atmospheric pressure conditions. It is prophesied that NICE-AAS could provide such high detection sensitivity that the instrumentation should not, by itself, be the limiting factor of an assessment of elemental abundance; the accuracy of an assessment would then instead be limited by concomitant species, e.g. originating from the handling procedures of the sample or the environment.
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| 2. |
- Forssén, Clayton, et al.
(författare)
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A transportable refractometer for assessment of pressure in the kPa range with ppm level precision
- 2020
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Ingår i: Acta IMEKO. - : International Measurement Confederation (IMEKO). - 0237-028X .- 2221-870X. ; 9:5, s. 287-292
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Tidskriftsartikel (refereegranskat)abstract
- A transportable refractometer for assessment of kPa pressures with ppm level precision is presented. It is based on the GAs MOdulation Refractometry (GAMOR) methodology, making it resistant to fluctuations and drifts. At the National Metrology Institute at RISE, Sweden, the system assessed pressures in the 4.3 - 8.7 kPa range with sub-ppm precision (0.5 - 0.9 ppm). The system was thereafter disassembled, packed, and transported 1040 km to Umeå University, where it, after unpacking and reassembling, demonstrated a similar precision (0.8 - 2.1 ppm). This shows that the system can be disassembled, packed, transported, unpacked, and reassembled with virtually unchanged performance.
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| 3. |
- Hausmaninger, Thomas, et al.
(författare)
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Depletion of the vibrational ground state of CH4 in absorption spectroscopy at 3.4 μm in N2 and air in the 1-100Torr range
- 2018
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0022-4073 .- 1879-1352. ; 205, s. 59-70
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Tidskriftsartikel (refereegranskat)abstract
- A model presented in an accompanying work predicts that mid-IR absorption signals from methane in trace concentrations in various buffer gases detected at pressures in the 1-100Torr range can be reduced and distorted due to depletion of the vibrational ground state if the molecules are exposed to laser powers in the tens of mW range or above. This work provides experimental evidence of such depletion in a resonant cavity under a variety of conditions, e.g. for intracavity laser powers up to 2W and for buffer gases of N-2 or dry air, and verifies the applicability of the model. It was found that the degree of depletion is significantly larger in N-2 than dry air, and that it increases with pressure for pressures up to around 10Torr (attributed to a decreased diffusion rate) but decreases with pressure for pressures above 20Torr (caused by an increased collisional vibrational decay rate). The maximum degree of depletion (similar to 80%) was obtained for methane in N-2 at around 15Torr. This implies that absorption spectrometry of methane can experience significant non-linear dependencies on laser power, pressure, as well as buffer gas composition. It is shown that depletion takes place also in (CH4)-C-13, which verifies the applicability of the model also for this isotopologue, and that NICE-OHMS signals detected in absorption phase are less affected by depletion than in dispersion. It was concluded that the absorption mode of detection can provide concentration assessments that are virtually free of influence of depletion for intracavity powers below 0.8 W.
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| 4. |
- Hausmaninger, Thomas, 1987-, et al.
(författare)
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Doppler-broadened mid-infrared NICE-OHMS system based on an optical parametric oscillator
- 2016
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Ingår i: Laser Applications to Chemical, Security and Environmental Analysis. - : Optica Publishing Group (formerly OSA). - 9781943580156
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Konferensbidrag (refereegranskat)abstract
- An OPO-based NICE-OHMS instrument for trace gas detection addressing fundamental vibration transitions in the mid-IR (3.2-3.9 µm) range has been developed. It shows a detection sensitivity for CH4 of 2.4×10−10cm−1Hz−1∕2 (corresponding to low ppt concentrations).
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| 5. |
- Hausmaninger, Thomas, 1987-, et al.
(författare)
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Doppler-broadened NICE-OHMS beyond the cavity-limited weak absorption condition – II : experimental verification
- 2016
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier. - 0022-4073 .- 1879-1352. ; 168, s. 245-256
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Tidskriftsartikel (refereegranskat)abstract
- Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) is normally described by an expression, here termed the conventional (CONV) description, that is restricted to the conventional cavity-limited weak absorption condition (CCLWA), i.e. when the single pass absorbance is significantly smaller than the empty cavity losses, i.e. when α0L<<π/F. To describe NICE-OHMS signals beyond this limit two simplified extended descriptions (termed the extended locking and extended transmission description, ELET, and the extended locking and full transmission description, ELFT), which are assumed to be valid under the relaxed cavity-limited weak absorption condition (RCLWA), i.e. when α0L<π/Fα0L<π/F, and a full description (denoted FULL), presumed to be valid also when the α0L<π/Fα0L<π/F condition does not hold, have recently been derived in an accompanying work (Ma W, et al. Doppler-broadened NICE-OHMS beyond the cavity-limited weak absorption condition - I. Theoretical Description. J Quant Spectrosc Radiat Transfer, 2015, http://dx.doi.org/10.1016/j.jqsrt.2015.09.007, this issue). The present work constitutes an experimental verification and assessment of the validity of these, performed in the Doppler limit for a set of Fα0L/πFα0L/π values (up to 3.5); it is shown under which conditions the various descriptions are valid. It is concluded that for samples with Fα0L/πFα0L/π up to 0.01, all descriptions replicate the data well. It is shown that the CONV description is adequate and provides accurate assessments of the signal strength (and thereby the analyte concentration) up to Fα0L/πFα0L/π of around 0.1, while the ELET is accurate for Fα0L/πFα0L/π up to around 0.3. The ELFT description mimics the Db NICE-OHMS signal well for Fα0L/πFα0L/π up to around unity, while the FULL description is adequate for all Fα0L/πFα0L/π values investigated. Access to these descriptions both increases considerably the dynamic range of the technique and facilitates calibration using certified reference gases, which thereby significantly broadens the applicability of the Db NICE-OHMS technique.
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| 6. |
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| 7. |
- Hausmaninger, Thomas, 1987-
(författare)
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Mid- and near-infrared NICE-OHMS : techniques for ultra-sensitive detection of molecules in gas phase
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) is a technique for ultra-sensitive detection of molecular absorption and dispersion. For highest performance, the technique combines cavity enhancement (CE) with frequency modulation (FM); while the former increases the effective interaction length between the light and the analyte by several orders of magnitudes, the latter removes the in-coupling of 1/f noise and makes the signals background free. The combination of CE and FM also gives the technique an immunity to amplitude noise caused by the jitter of the laser frequency relative to the cavity resonance frequencies. All these properties make the technique suitable for ultra sensitive trace gas detection in the sub-parts-per-trillion (ppt) range. The aim of this thesis is to improve the performance of the NICE-OHMS technique and to increase its range of applications.The work in this thesis can be divided into three areas:Firstly, a mid-infrared (MIR)-NICE-OHMS instrumentation was developed. In a first realization an unprecedented white-noise equivalent absorption limit for Doppler broadened (Db) detection in the MIR of 3×10-9 cm-1Hz-1/2was demonstrated. This was subsequently improved to 2.4×10-10 cm-1Hz-1/2allowing for detection methane and its two main isotopologues (CH3D and 13CH4) at their natural abundance.Secondly, further development of an existing near-infrared NICE-OHMS system was performed. This resulted in an improved longtime stability and the first shot-noise limited NICE-OHMS system for Db detection with a noise equivalent absorption limit of 2.3×10-14 cm-1detected over 200 s. Thirdly, models and theoretical descriptions of NICE-OHMS signals under strong absorption conditions and from methane under high laser power were developed. It was experimentally verified that the models allow for a more accurate evaluation of NICE-OHMS signals under a wide range of conditions.
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| 8. |
- Hausmaninger, Thomas, 1987-, et al.
(författare)
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Model for molecular absorption spectroscopy in the 1-100 Torr range in the presence of vibrational depletion - Applied to CH4 in N2 and dry air
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- When molecules whose collision induced vibrational decay rates are small are probed by molecular absorption spectroscopic (MAS) techniques the absorption signal can, under certain conditions, be reduced and distorted. The reason has been attributed to the fact that a substantial fraction of the molecules in the interaction region will reside in excited vibrational states, which leads to a depletion of the vibrational ground state. One type of molecule in which this can take place is methane. A model for this phenomenon, based on CH4 in trace concentrations in either N2 or dry air in a cylindrical gas cell, detected by mid-infrared light in the 1 - 100 Torr pressure range, is presented. Due to a fast collisional coupling between various rotational states and velocity groups we suggest that depletion in MAS can be modeled adequately by a simple three-level system to which the transport of molecules in the system is coupled as diffusion according to Fick's law, applied to each level individually. The model is verified in a separate work [Hausmaninger T et al., J Quant Spectrosc Radiat Tr. 2017;205:59-70] with good agreement. It predicts that depletion has a strong pressure dependence in the 1 - 30 Torr range, that it is significantly more pronounced in N2 than in air, and that considerable degrees of depletion can be obtained for mW powers of light (> 10% for powers > 20 mW). The findings indicate that, unless precautions are taken, depletion can adversely affect quantitative assessments performed by MAS. Means of how to reduce depletion are given.
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| 9. |
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| 10. |
- Johansson, Alexandra C., et al.
(författare)
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Broadband calibration-free cavity-enhanced complex refractive index spectroscopy using a frequency comb
- 2018
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 26:16, s. 20633-20648
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Tidskriftsartikel (refereegranskat)abstract
- We present broadband cavity-enhanced complex refractive index spectroscopy (CE-CRIS), a technique for calibration-free determination of the complex refractive index of entire molecular bands via direct measurement of transmission modes of a Fabry-Perot cavity filled with the sample. The measurement of the cavity transmission spectrum is done using an optical frequency comb and a mechanical Fourier transform spectrometer with sub-nominal resolution. Molecular absorption and dispersion spectra (corresponding to the imaginary and real parts of the refractive index) are obtained from the cavity mode broadening and shift retrieved from fits of Lorentzian profiles to the individual cavity modes. This method is calibration-free because the mode broadening and shift are independent of the cavity parameters such as the length and mirror reflectivity. In this first demonstration of broadband CE-CRIS we measure simultaneously the absorption and dispersion spectra of three combination bands of CO2 in the range between 1525 nm and 1620 nm and achieve good agreement with theoretical models. This opens up for precision spectroscopy of the complex refractive index of several molecular bands simultaneously.
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| 11. |
- Johansson, Alexandra C., 1987-, et al.
(författare)
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Broadband Complex Refractive Index Spectroscopy via Measurement of Cavity Modes
- 2018
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Ingår i: 2018 Conference on Lasers and Electro-Optics (CLEO). - : IEEE. - 9781943580422
-
Konferensbidrag (refereegranskat)abstract
- We retrieve high precision absorption and dispersion spectra of the 3v(1)+v(3) band of CO2 from direct measurement of cavity transmission modes using an optical frequency comb and a mechanical Fourier transfolin spectrometer with sub-nominal resolution.
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| 12. |
- Johansson, Alexandra C., 1987-, et al.
(författare)
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Cavity-enhanced complex refractive index spectroscopy of entire molecular bands using a frequency comb
- 2018
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Ingår i: Optics InfoBase Conference Papers. - : Optica Publishing Group. - 9781943580477
-
Konferensbidrag (refereegranskat)abstract
- We demonstrate broadband calibration-free complex refractive index spectroscopy of entire molecular bands by direct measurement of transmission modes of a Fabry-Perot cavity using frequency comb-based Fourier transform spectrometer with sub-nominal resolution.
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| 13. |
- Johansson, Alexandra C., 1987-, et al.
(författare)
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Precise comb-based fourier transform spectroscopy for line parameter retrieval
- 2019
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Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference (CLEO/EUROPE-EQEC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728104690
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Konferensbidrag (refereegranskat)abstract
- Accurate parameters of molecular transitions are needed for data analysis in many applications, ranging from atmospheric research to astrophysics and determination of fundamental constants. Optical frequency comb Fourier transform spectroscopy (OFC-FTS) is particularly well-suited for high-precision measurements of broadband molecular spectra. From these spectra, the parameters of individual transitions - all measured simultaneously under the same experimental conditions - can be determined. We use a mechanical OFC-FTS spectrometer with sub-nominal resolution [1, 2] to perform precise broadband measurements of entire molecular bands of CO2 using either direct absorption spectroscopy or cavity-enhanced complex refractive index spectroscopy (CE-CRIS) [3] and we extract line parameters for line shapes beyond the Voigt profile.
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| 14. |
- Ma, Weiguang, et al.
(författare)
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Doppler-broadened NICE-OHMS beyond the cavity-limited weak absorption condition – I. Theoretical Description
- 2016
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 168, s. 217-244
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) is conventionally described by an expression (here referred to as the CONV expression) that is restricted to the case when the single-pass absorbance, α0L, is much smaller than the empty cavity losses, π/F [here termed the conventional cavity-limited weak absorption (CCLWA) condition]. This limits the applicability of the technique, primarily its dynamic range and calibration capability. To remedy this, this work derives extended descriptions of Db NICEOHMS that are not restricted to the CCLWA condition. First, the general principles of Db NICEOHMS are scrutinized in some detail. Based solely upon a set of general assumptions, predominantly that it is appropriate to linearize the Beer–Lambert law, that the light is modulated to a triplet, and that the Pound–Drever–Hall sidebands are fully reflected, a general description of Db NICE-OHMS that is not limited to any specific restriction on α0L vs. π/F, here referred to as the FULL description, is derived. However, this description constitutes a set of equations to which no closed form solution has been found. Hence, it needs to be solved numerically (by iterations), which is inconvenient. To circumvent this, for the cases when α0Loπ/F but without the requirement that the stronger CCLWA condition needs to be fulfilled, a couple of simplified extended expressions that are expressible in closed analytical form, referred to as the extended locking and extended transmission description, ELET, and the extended locking and full transmission description, ELFT, have been derived. An analysis based on simulations validates the various descriptions and assesses to which extent they agree. It is shown that in the CCLWA limit, all extended descriptions revert to the CONV expression. The latter one deviates though from the extended ones for α0L around and above 0.1π/F. The two simplified extended descriptions agree with the FULL description for a larger range of α0L than the CONV expression, viz. for the ELET description for α0L up to 0.3π/F and for ELFT for α0L up to 0.6 or 1.0 π/F (depending on the mode of detection). It is then demonstrated that the conventional view of Db NICE-OHMS, which states that the out-of-phase and the in-phase signals can be referred to as a pure absorption and dispersion signal, respectively, breaks down when the CCLWA condition does not hold. In this case, the out-of-phase signal is additionally affected by the phase shifts of the laser components (i.e. dispersion) while the in-phase signal is also influenced by their attenuation. Access to new descriptions broadens considerably the dynamic range of Db NICE-OHMS and facilitates calibration using standard references samples, and thereby its applicability
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| 15. |
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| 16. |
- Rutkowski, Lucile, et al.
(författare)
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Sensitive and broadband measurement of dispersion in a cavity using a Fourier transform spectrometer with kHz resolution
- 2017
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:18, s. 21711-21718
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Tidskriftsartikel (refereegranskat)abstract
- Optical cavities provide high sensitivity to dispersion since their resonance frequencies depend on the index of refraction. We present a direct, broadband, and accurate measurement of the modes of a high finesse cavity using an optical frequency comb and a mechanical Fourier transform spectrometer with a kHz-level resolution. We characterize 16000 longitudinal cavity modes spanning 16 THz of bandwidth in terms of center frequency, linewidth, and amplitude. Using the center frequencies we retrieve the group delay dispersion of the cavity mirror coatings and pure N2 with 0.1 fs2 precision and 1 fs2 accuracy, as well as the refractivity of the 3ν1 +ν3 absorption band of CO2 with 5 × 10‒12 precision. This opens up for broadband refractive index metrology and calibration-free spectroscopy of entire molecular bands.
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| 17. |
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| 18. |
- Silander, Isak, et al.
(författare)
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Doppler-broadened mid-infrared noise-immune cavity-enhanced optical heterodyne molecular spectrometry based on an optical parametric oscillator for trace gas detection
- 2015
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 40:4, s. 439-442
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Tidskriftsartikel (refereegranskat)abstract
- An optical parametric oscillator based Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) system suitable for addressing fundamental vibrational transitions in the 3.2-3.9 mu m mid-infrared (MIR) region has been realized. An Allan-Werle analysis provides a detection sensitivity of methane of 1.5 x 10-9 cm(-1) with a 20 s integration time, which corresponds to 90 ppt of CH4 if detected at the strongest transition addressed at 40 Torr. This supersedes that of previous Db MIR NICE-OHMS demonstrations and suggests that the technique can be suitable for detection of both the environmentally important (CH4)-C-13 and CH3D isotopologues. It also opens up for detection of many other molecular species at ppt and sub-ppt concentration levels.
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| 19. |
- Silander, Isak, 1980-, et al.
(författare)
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Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry down to 4 x 10-13 cm-1 Hz-1/2 : implementation of a 50,000 finesse cavity
- 2015
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Ingår i: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 40:9, s. 2004-2007
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Tidskriftsartikel (refereegranskat)abstract
- We report on the realization of a Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) instrumentation based on a high-finesse (50,000) cavity with a detection sensitivity of 4 x 10(-13) cm(-1) Hz(-1/2). For the P-e(11) transition targeted at 1.5316 mu m, this corresponds to a C2H2 concentration of 240 ppq (parts-per-quadrillion) detected at 100 Torr. The setup was originally affected by recurrent dips in the cavity transmission, which were attributed to excitation of high-order transverse mode by scattering from the mirrors. The effect of these was reduced by insertion of a small pinhole in the cavity.
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| 20. |
- Silander, Isak, 1980-, et al.
(författare)
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Gas equilibration gas modulation refractometry for assessment of pressure with sub-ppm precision
- 2019
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Ingår i: Journal of Vacuum Science and Technology B. - : AVS Science and Technology Society. - 2166-2746 .- 2166-2754. ; 37:4
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Tidskriftsartikel (refereegranskat)abstract
- Gas modulation refractometry (GAMOR) is a methodology that, by performing repeated reference assessments with the measurement cavity being evacuated while the reference cavity is held at a constant pressure, can mitigate drifts in dual Fabry-Perot cavity based refractometry. A novel realization of GAMOR, referred to as gas equilibration GAMOR, that outperforms the original realization of GAMOR, here referred to as single cavity modulated GAMOR (SCM-GAMOR), is presented. In this, the reference measurements are carried out by equalizing the pressures in the two cavities, whereby the time it takes to reach adequate conditions for the reference measurements has been reduced. This implies that a larger fraction of the measurement cycle can be devoted to data acquisition, which reduces white noise and improves on its short-term characteristics. The presented realization also encompasses a new cavity design with improved temperature stabilization and assessment. This has contributed to improved long-term characteristics of the GAMOR methodology. The system was characterized with respect to a dead weight pressure balance. It was found that the system shows a significantly improved precision with respect to SCM-GAMOR for all integration times. For a pressure of 4303 Pa, it can provide a response for short integration times (up to 10 min) of 1.5 mPa (cycle)1/2, while for longer integration times (up to 18 h), it shows an integration time-independent Allan deviation of 1 mPa (corresponding to a precision, defined as twice the Allan deviation, of 0.5 ppm), exceeding the original SCM-GAMOR system by a factor of 2 and 8, respectively. When used for low pressures, it can provide a precision in the sub-mPa region; for the case with an evacuated measurement cavity, the system provided, for up to 40 measurement cycles (ca. 1.5 h), a white noise of 0.7 mPa (cycle)1/2, and a minimum Allan deviation of 0.15 mPa. It shows a purely linear response in the 2.8-10.1 kPa range. This implies that the system can be used for the transfer of calibration over large pressure ranges with exceptional low uncertainty. © 2019 Author(s).
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| 21. |
- Silander, Isak, 1980-, et al.
(författare)
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Gas modulation refractometry for high-precision assessment of pressure under nonerature-stabilized conditions
- 2018
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 36:3
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Tidskriftsartikel (refereegranskat)abstract
- The authors report on the realization of a novel methodology for refractometry - GAs modulation refractometry (GAMOR) - that decreases the influence of drifts in Fabry Perot cavity refractometry. The instrumentation is based on a dual Fabry-Perot cavity refractometer in which the beat frequency between the light fields locked to two different cavities, one measurement and one reference cavity, is measured. The GAMOR methodology comprises a process in which the measurement cavity sequentially is filled and evacuated while the reference cavity is constantly evacuated. By performing beat frequency measurements both before and after the finite-pressure measurement, zero point references are periodically created. This opens up for high precision refractometry under nontemperature-stabilized conditions. A first version of an instrumentation based on the GAMOR methodology has been realized and its basic performance has been scrutinized. The refractometer consists of a Zerodur cavity-block and tunable narrow linewidth fiber lasers operating within the C34 communication channel (i.e., around 1.55 μm) at which there are a multitude of fiber coupled off-the-shelf optical, electro-optic, and acousto-optic components. The system is fully computer controlled, which implies it can perform unattended gas assessments over any foreseeable length of time. When applied to a system with no active temperature stabilization, the GAMOR methodology has demonstrated a 3 orders of magnitude improvement of the precision with respect to conventional static detection. When referenced to a dead weight pressure scale the instrumentation has demonstrated assessment of pressures in the kilo-Pascal range (4303 and 7226 Pa) limited by white noise with standard deviations in the 3.2 N - 1 / 2 - 3.5 N - 1 / 2 mPa range, where N is the number of measurement cycles (each being 100 s long). For short measurement times (up to around 103 s), the system exhibits a (1 σ) total relative precision of 0.7 (0.5) ppm for assessment of pressures in the 4 kPa region and 0.5 (0.4) ppm for pressures around 7 kPa, where the numbers in parentheses represent the part of the total noise that has been attributed to the refractometer. As long as the measurement procedure is performed over short time scales, the inherent properties of the GAMOR methodology allow for high precision assessments by the use of instrumentation that is not actively temperature stabilized or systems that are affected by outgassing or leaks. They also open up for a variety of applications within metrology; e.g., transfer of calibration and characterization of pressure gauges, including piston gauges.
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| 22. |
- Silander, Isak, 1980-, et al.
(författare)
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Model for in-coupling of etalons into signal strengths extracted from spectral line shape fitting and methodology for predicting the optimum scanning range : demonstration of Doppler-broadened, noise-immune, cavity-enhanced optical heterodyne molecular spectroscopy down to 9 × 10−14 cm−1
- 2015
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - : Optical Society of America. - 0740-3224 .- 1520-8540. ; 32:10, s. 2104-2114
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Tidskriftsartikel (refereegranskat)abstract
- Expressions for the in-coupling of white noise and etalons into fitted signal strengths are derived. These show that the amount of noise picked up is affected by the scanning range. A methodology for finding the optimum scanning range from a single set of measurements has been developed. This was used to estimate the optimum conditions of a noise-immune, cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) setup. The methodology was validated by measurements. This resulted in a spectral noise equivalent absorption per unit length of 2.6 × 10−13 cm−1 Hz−1∕2 and a minimum Allan deviation of 9 × 10−14 cm−1 at 30 s, which are, to our knowledge, the lowest reported for Doppler-broadened NICE-OHMS
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| 23. |
- Talyzin, Alexandr, et al.
(författare)
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The structure of graphene oxide membranes in liquid water, ethanol and water – ethanol mixtures
- 2014
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Ingår i: Nanoscale. - : RSC Publishing. - 2040-3364 .- 2040-3372. ; 6, s. 272-281
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Tidskriftsartikel (refereegranskat)abstract
- The structure of graphene oxide (GO) membranes was studied in situ in liquid solvents using synchrotron radiation X-ray diffraction in a broad temperature interval. GO membranes are hydrated by water similarly to precursor graphite oxide powders but intercalation of alcohols is strongly hindered, which explains why the GO membranes are permeated by water and not by ethanol. Insertion of ethanol into the membrane structure is limited to only one monolayer in the whole studied temperature range, in contrast to precursor graphite oxide powders, which are intercalated with up to two ethanol monolayers (Brodie) and four ethanol monolayers (Hummers). As a result, GO membranes demonstrate the absence of “negative thermal expansion” and phase transitions connected to insertion/de-insertion of alcohols upon temperature variations reported earlier for graphite oxide powders. Therefore, GO membranes are a distinct type of material with unique solvation properties compared to parent graphite oxides even if they are composed of the same graphene oxide flakes.
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| 24. |
- Zhao, Gang, et al.
(författare)
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Differential noise-immune cavity-enhanced optical heterodyne molecular spectroscopy for improvement of the detection sensitivity by reduction of drifts from background signals
- 2017
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:23, s. 29454-29471
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Tidskriftsartikel (refereegranskat)abstract
- The detection sensitivity of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is often limited by background signals that bring in drifts. A novel realization of NICE-OHMS, termed differential NICE-OHMS, that both reduces such drifts and enlarges the molecular signal is presented. It is based on simultaneous detection of NICE-OHMS signals in reflection and transmission, followed by a subtraction of the former (properly weighted) from the latter. An Allan plot analysis shows that the instrumentation could demonstrate a noise equivalent absorption per unit length (NEAL) of 4.7 × 10−14 cm−1, obtained for an integration time of 170 s.
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| 25. |
- Zhao, Gang, et al.
(författare)
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High-resolution trace gas detection by sub-Doppler noise-immune cavity-enhanced optical heterodyne molecular spectrometry : application to detection of acetylene in human breath
- 2019
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 27:13, s. 17940-17953
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Tidskriftsartikel (refereegranskat)abstract
- A sensitive high-resolution sub-Doppler detecting spectrometer, based on noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS), for trace gas detection of species whose transitions have severe spectral overlap with abundant concomitant species is presented. It is designed around a NICE-OHMS instrumentation utilizing balanced detection that provides shot-noise limited Doppler-broadened (Db) detection. By synchronous dithering the positions of the two cavity mirrors, the effect of residual etalons between the cavity and other surfaces in the system could be reduced. An Allan deviation of the absorption coefficient of 2.2 × 10-13 cm-1 at 60 s, which, for the targeted transition in C2H2, corresponds to a 3σ detection sensitivity of 130 ppt, is demonstrated. It is shown that despite significant spectral interference from CO2 at the targeted transition, which precludes Db detection of C2H2, acetylene could be detected in exhaled breath of healthy smokers.
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| 26. |
- Zhao, Gang, et al.
(författare)
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High resolution ultra-sensitive trace gas detection by use of cavity-position-modulated sub-Doppler NICE-OHMS - Application to detection of acetylene in human breath
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A sensitive high resolution spectrometer for trace gas detection of species whose transitions have severe spectral overlap with abundant concomitant species by sub-Doppler (sD) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) is presented. The setup is based on a NICE-OHMS instrumentation utilizing balanced detection that provides shot-noise limited Doppler-broadened (Db) detection. An additional layer of modulation is added to reduce the influence of narrow etalons and improve the sensitivity for sD detection. By dithering synchronously the positions of the two cavity mirrors, the effect of residual etalons between one of the cavity mirrors and another surface in the system could be reduced without affecting the frequencies of the cavity mode. This reduced the drifts in the system, allowing for an Allan deviation of the absorption coefficient of 2.2×10−13 cm−1 for an integration time of 60 s, which, for the targeted C2H2 transition at 6518.4858 cm−1, corresponds to a 3σ detection sensitivity of 130 ppt. Sub-Doppler trace gas detection is demonstrated by measuring ppb levels of C2H2 in the exhaled breath of smokers. A procedure was worked out for simultaneous detection of CO2, based on the Db response. It is shown that despite significant spectral interference from CO2, which precludes Db detection of C2H2 in breath, acetylene could be detected in breath from smokers with good spectral resolution by the use of sD NICE-OHMS.
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| 27. |
- Zhao, Gang, et al.
(författare)
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Shot-noise-limited Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry
- 2018
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 43:4, s. 715-718
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Tidskriftsartikel (refereegranskat)abstract
- Shot-noise-limited Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) has been realized by implementation of balanced detection. A characterization of the system based on Allan-Werle plots of the absorption coefficient, retrieved by fitting a model function to data, shows that the system has a white noise equivalent absorption per unit length per square root of bandwidth of 2.3 x 10(-13) cm(-1) Hz(-1/2), solely 44% above the shot noise limit, and a detection sensitivity of 2.2 x 10(-14) cm(-1) over 200 s, both being unprecedented for Db NICE-OHMS. The white noise response follows the expected inverse square root dependence on power that is representative of a shot-noise-limited response, which confirms that the system is shot-noise-limited.
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| 28. |
- Zhao, Gang, et al.
(författare)
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Whispering-gallery-mode laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry
- 2017
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Ingår i: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 42:16, s. 3109-3112
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Tidskriftsartikel (refereegranskat)abstract
- The whispering-gallery-mode (WGM) laser is a type of laser that has an exceptionally narrow linewidth. Noise-immune cavity-enhanced optical heterodyne molecular spectrometry, which is a detection technique with extraordinary properties that benefit from narrow linewidth lasers, has been realized with a WGM laser. By locking to a cavity with a finesse of 55 000, acetylene and carbon dioxide could be simultaneously detected down to an unprecedented noise equivalent absorption per unit length of 6.6 x 10(-14) cm(-1) over 150 s, corresponding to 5 ppt of C2H2.
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