198 research outputs found
Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared - application to trace detection of H2O2
We demonstrate the first cavity-enhanced optical frequency comb spectroscopy
in the mid-infrared wavelength region and report the sensitive real-time trace
detection of hydrogen peroxide in the presence of a large amount of water. The
experimental apparatus is based on a mid-infrared optical parametric oscillator
synchronously pumped by a high power Yb:fiber laser, a high finesse broadband
cavity, and a fast-scanning Fourier transform spectrometer with autobalancing
detection. The comb spectrum with a bandwidth of 200 nm centered around 3.75
{\mu}m is simultaneously coupled to the cavity and both degrees of freedom of
the comb, i.e., the repetition rate and carrier envelope offset frequency, are
locked to the cavity to ensure stable transmission. The autobalancing detection
scheme reduces the intensity noise by a factor of 300, and a sensitivity of 5.4
{\times} 10^-9 cm^-1 Hz^-1/2 with a resolution of 800 MHz is achieved
(corresponding to 6.9 {\times} 10^-11 cm^-1 Hz^-1/2 per spectral element for
6000 resolved elements). This yields a noise equivalent detection limit for
hydrogen peroxide of 8 parts-per-billion (ppb); in the presence of 2.8% of
water the detection limit is 130 ppb. Spectra of acetylene, methane and nitrous
oxide at atmospheric pressure are also presented, and a line shape model is
developed to simulate the experimental data.Comment: submitted to special FLAIR 2011 issue of Appl. Phys.
Line positions and intensities of the band of CHI using mid-infrared optical frequency comb Fourier transform spectroscopy
We present a new spectral analysis of the and
+- bands of CHI around 2971 cm
based on a high-resolution spectrum spanning from 2800 cm to 3160
cm, measured using an optical frequency comb Fourier transform
spectrometer. From this spectrum, we previously assigned the and
+- bands around 3060 cm using PGOPHER, and
the line list was incorporated in the HITRAN database. Here, we treat the two
fundamental bands, and , together with the perturbing
states, 2+ and +2, as a four-level
system connected via Coriolis and Fermi interactions. A similar four-level
system is assumed to connect the +- and
+- hot bands, which appear due to the population of
the low-lying state at room temperature, with the
2+2 and +- perturbing
states. This treatment provides a good global agreement of the simulated
spectra with experiment, and hence accurate line lists and band parameters of
the four connected vibrational states in each system. Overall, we assign 4665
transitions in the fundamental band system, with an average error of 0.00071
cm, a factor of two better than earlier work on the band using
conventional Fourier transform infrared spectroscopy. The band shows
hyperfine splitting, resolvable for transitions with J 2 x K. Finally,
the spectral intensities of 65 lines of the band and 7 lines of the
+- band are reported for the first time using the
Voigt line shape as a model in multispectral fitting
Sensitive and broadband measurement of dispersion in a cavity using a Fourier transform spectrometer with kHz resolution
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 cavity modes spanning 16 THz of bandwidth in
terms of center frequency, linewidth, and amplitude. We retrieve the group
delay dispersion of the cavity mirror coatings and pure N with 0.1
fs precision and 1 fs accuracy, as well as the refractivity of the
3{\nu}1+{\nu}3 absorption band of CO with 5 x 10 precision.
This opens up for broadband refractive index metrology and calibration-free
spectroscopy of entire molecular bands
OPTICAL FREQUENCY COMB FOURIER TRANSFORM SPECTROSCOPY
Fourier transform spectroscopy (FTS) based on optical frequency combs offers a number of advantages over conventional Fourier transform infrared (FTIR) spectroscopy based on incoherent sources\footnote{J. Mandon, G. Guelachvili, and N. Picque, Nat. Photonics 3, 99 (2009).}. The high spectral brightness of the comb sources allows measuring spectra with high signal-to-noise ratios in acquisition times of the order of seconds. What is more, the resolution of comb-based FTS is given by the linewidth of the comb modes rather than the optical path difference (OPD) in the spectrometer, provided that the OPD is matched to the inverse of the comb mode spacing\footnote{P. Maslowski, et al., Phys. Rev. A 93, 021802 (2016); L. Rutkowski, et al., J. Quant. Spectrosc. Radiat. Transf. 204, 63 (2018).}. This implies that spectra with kHz resolution can be measured using OPD of the order of a few tens of cm\footnote{L. Rutkowski, et al., Opt. Express 25, 21711 (2017).}, which is impossible in conventional FTIR spectrometers. To increase the sensitivity of direct absorption measurements, frequency combs can be efficiently coupled into enhancement cavities that increase the interaction length with the sample\footnote{M. J. Thorpe, and J. Ye, Appl. Phys. B 91, 397 (2008); A. Foltynowicz, et al., Phys. Rev. Lett. 107, 233002 (2011).}. In another cavity-enhanced approach, the profiles of the cavity modes are measured directly, and complex refractive index spectra of entire molecular bands are determined from the broadening and shift of the cavity modes caused by the molecular sample\footnote{A. C. Johansson, et al., Opt. Express 26, 20633 (2018).}. Comb-based FTS can also be combined with other detection methods, such as Faraday rotation spectroscopy to detect broadband interference-free spectra of paramagnetic molecules\footnote{A. C. Johansson, J. Westberg, G. Wysocki, and A. Foltynowicz, Appl. Phys. B 124, 79 (2018).}, or photoacoustic spectroscopy that allows detection in a very small sample volume\footnote{I. Sadiek, et al., Phys. Chem. Chem. Phys. 20, 27849 (2018).}. I will present the various implementations of comb-based FTS and show examples of high-resolution measurements of entire absorption bands in the near- and mid-infrared wavelength range
Electro-anatomical mapping of the left atrium before and after cryothermal balloon isolation of the pulmonary veins
Introduction: The 28 mm cryoballoon catheter is a device used for pulmonary vein isolation (PVI). The aim of this study was to evaluate the extent of the ablation in the antral regions of the left atrium. Methods and Results: Eighteen patients with drug refractory, symptomatic, paroxysmal AF were enrolled. A 3D electroanatomic reconstruction of the left atrium was made before and after successful PVI with the 28 mm cryoballoon. Markers were placed at the ostium. Sixteen patients were mapped. Fourteen patients had 4 veins each, and 2 patients had a common ostium of the left sided veins. All separate ostia were isolated in the antral region. The two common ostia showed ostial isolation. There was a significant difference in vein size between the common (29 and 31 mm) and the separate ostia (19∈±∈4 mm) (p∈<∈0.01). The performance of an additional segmental ablation if balloon PVI did not eliminate all electrical activity, did not influence the extent of the ablation. The earliest left atrial activation during sinus rhythm was located in the superior septal region before ablation in all patients. After ablation, two patients showed a substantial downward shift towards the middle and inferior septal region respectively (NS). Four patients demonstrated a slight downward shift of the first activation. Conclusions: In cryoballoon PVI, the majority of the veins undergo antral isolation. Veins with a diameter larger than the balloon, are isolated ostially. In individual cases, the left atrial activation sequence appears to be altered after ablation
Quantum-noise-limited optical frequency comb spectroscopy
We achieve a quantum-noise-limited absorption sensitivity of
1.7/times10 cm per spectral element at 400 s of acquisition time
with cavity-enhanced frequency comb spectroscopy, the highest demonstrated for
a comb-based technique. The system comprises a frequency comb locked to a
high-finesse cavity and a fast-scanning Fourier transform spectrometer with an
ultra-low-noise autobalancing detector. Spectra with a signal-to-noise ratio
above 1000 and a resolution of 380 MHz are acquired within a few seconds. The
measured absorption lineshapes are in excellent agreement with theoretical
predictions.Comment: 18 pages, 4 figures; http://prl.aps.org/pdf/PRL/v107/i23/e23300
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