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Dive into the research topics where Alexis Bohlin is active.

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Featured researches published by Alexis Bohlin.


Journal of Chemical Physics | 2013

Communication: Two-dimensional gas-phase coherent anti-Stokes Raman spectroscopy (2D-CARS): Simultaneous planar imaging and multiplex spectroscopy in a single laser shot

Alexis Bohlin; Christopher J. Kliewer

Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a powerful tool for chemical sensing, molecular dynamics measurements, and rovibrational spectroscopy since its development over 30 years ago, finding use in fields of study as diverse as combustion diagnostics, cell biology, plasma physics, and the standoff detection of explosives. The capability for acquiring resolved CARS spectra in multiple spatial dimensions within a single laser shot has been a long-standing goal for the study of dynamical processes, but has proven elusive because of both phase-matching and detection considerations. Here, by combining new phase matching and detection schemes with the high efficiency of femtosecond excitation of Raman coherences, we introduce a technique for single-shot two-dimensional (2D) spatial measurements of gas phase CARS spectra. We demonstrate a spectrometer enabling both 2D plane imaging and spectroscopy simultaneously, and present the instantaneous measurement of 15,000 spatially correlated rotational CARS spectra in N2 and air over a 2D field of 40 mm(2).


Journal of Chemical Physics | 2013

Communication: Simplified two-beam rotational CARS signal generation demonstrated in 1D

Alexis Bohlin; Brian D. Patterson; Christopher J. Kliewer

We explore a novel phase matching scheme for gas-phase rotational coherent anti-Stokes Raman spectroscopy (CARS). The scheme significantly simplifies the employment of the technique in general. Two laser beams, one broadband and one narrowband, are crossed at arbitrary angle and the generated rotational CARS signal, copropagating with the probe beam, is isolated using a polarization gating technique. The effect of phase-vector mismatch for various experimental implementations was measured experimentally and compared to calculations. The spatial resolution of the current technique is improved by more than an order of magnitude over standard gas-phase CARS experimental arrangements, providing an interaction length of less than 50 μm when desired. Both the pump and Stokes photons originate from the broadband pulse, and are therefore automatically overlapped temporally and spatially. Significantly improved signal levels are achieved because of both the ease of alignment and the higher pulse energy available to the pump and Stokes fields. We demonstrate the technique for single-laser-shot 1D rotational CARS signal generation over approximately a 1 cm field in a flame.


Journal of Physical Chemistry Letters | 2015

Direct Coherent Raman Temperature Imaging and Wideband Chemical Detection in a Hydrocarbon Flat Flame.

Alexis Bohlin; Christopher J. Kliewer

A single-shot coherent Raman imaging technique has been developed for spatially correlated one-dimensional high-fidelity gas-phase thermometry and multiplex chemical detection in flames. The technique utilizes two-beam phase matching, operating a single ultrashort pump/Stokes excitation pulse (7 fs) and a narrowband picosecond probe pulse (70 ps), interrogating a Raman active window of ∼4200 cm(-1) with ∼0.3 cm(-1) spectral resolution. The measurement geometry is formed intersecting the two beams shaped as laser-sheets and the one-coordinate spatial information is retrieved with a linespread function of <40 μm. The advance provides the possibility for the multiplexed measurement of all combustion relevant major species simultaneously with gaseous temperature monitored over a several millimeter field of view. The current technique is optimized in a premixed hydrocarbon flat-flame. At the flame-front, it is shown that direct imaging renders the temperature profile within ∼1% inaccuracy, whereas typical point-wise raster scanning may have relative systematic deviations up to 15% due to spatial averaging effects.


Applied Physics Letters | 2014

Two-beam ultrabroadband coherent anti-Stokes Raman spectroscopy for high resolution gas-phase multiplex imaging

Alexis Bohlin; Christopher J. Kliewer

We propose and develop a method for wideband coherent anti-Stokes Raman spectroscopy (CARS) in the gas phase and demonstrate the single-shot measurement of N2, H2, CO2, O2, and CH4. Pure-rotational and vibrational O-, Q-, and S- branch spectra are collected simultaneously, with high spectral and spatial resolution, and within a single-laser-shot. The relative intensity of the rotational and vibrational signals can be tuned arbitrarily using polarization techniques. The ultrashort 7 fs pump and Stokes pulses are automatically overlapped temporally and spatially using a two-beam CARS technique, and the crossed probe beam allows for excellent spatial sectioning of the probed location.


Journal of Chemical Physics | 2012

Direct measurement of S-branch N(2)-H(2) Raman linewidths using time-resolved pure rotational coherent anti-Stokes Raman spectroscopy.

Alexis Bohlin; Emil Nordström; Brian D. Patterson; Per-Erik Bengtsson; Christopher J. Kliewer

S-branch N(2)-H(2) Raman linewidths have been measured in the temperature region 294-1466 K using time-resolved dual-broadband picosecond pure rotational coherent anti-Stokes Raman spectroscopy (RCARS). Data are extracted by mapping the dephasing rates of the CARS signal temporal decay. The J-dependent coherence decays are detected in the time domain by following the individual spectral lines as a function of probe delay. The linewidth data set was employed in spectral fits of N(2) RCARS spectra recorded in binary mixtures of N(2) and H(2) at calibrated temperature conditions up to 661 K using a standard nanosecond RCARS setup. In this region, the set shows a deviation of less than 2% in comparison with thermocouples. The results provide useful knowledge for the applicability of N(2) CARS thermometry on the fuel-side of H(2) diffusion flames.


Applied Spectroscopy | 2010

Effective suppression of stray light in rotational coherent anti-stokes Raman spectroscopy using an angle-tuned short-wave-pass filter.

Alexis Bohlin; Per-Erik Bengtsson

Stray light interference is a common problem in spontaneous rotational Raman spectroscopy and rotational coherent anti-Stokes Raman spectropscopy (CARS). The reason is that the detected spectrum appears in the spectral vicinity of the probe beam wavelength, and stray light at this wavelength from optics and surfaces is hard to suppress. In this Note, efficient suppression of stray light is demonstrated for rotational CARS measurements using a commercially available short-wave-pass filter. By angle-tuning this filter with a specified cut-off wavelength at 561 nm, the cut-off wavelength could be tuned to a desired spectral position so that more than 80% transmission is achieved as close as 15 cm−1 (∼0.4 nm) from the probe beam wavelength of 532.0 nm, while the intensity at this wavelength is suppressed by two orders of magnitude.


Combustion Science and Technology | 2013

Are Sooting Premixed Porous-Plug Burner Flames One-Dimensional? A Laser-Based Experimental Investigation

Nils-Erik Olofsson; Henrik Bladh; Alexis Bohlin; Jonathan Johnsson; Per-Erik Bengtsson

The one-dimensional character of sooting premixed porous-plug (McKenna) burner flames has been examined, motivated by recent investigations where the one-dimensionality has been questioned. The examination employs laser diagnostic techniques to measure different characteristics: temperature using rotational coherent anti-Stokes Raman spectroscopy (CARS) and soot properties using laser-induced incandescence and elastic light scattering. Special attention has been paid to the influence of an outer shroud gas flow of either nitrogen or air. The nitrogen shroud gas leads to flame cooling at the outer edge, whereas the air shroud results in heating through the oxidation of CO/H2/soot. This generally results in a more inhomogeneous spatial particle size profile for the nitrogen shroud flame, with smaller particle sizes at the flame edge. The present results emphasize the need to characterize burner and operating conditions accurately, and also, regarding parameters that at first glance seem less relevant, such as the shroud gas, to provide useful data for comparison between laboratories.


Laser Applications to Chemical, Security and Environmental Analysis | 2012

Development and Application of Rotational CARS Spectroscopy for Reacting Flows

Alexis Bohlin; Emil Nordström; Per-Erik Bengtsson

Rotational CARS is a useful diagnostic tool for reactive flows. The talk focuses on recent developments regarding temperature accuracy related to Herman-Wallis factors and Raman linewidths, major species concentration measurements, and applications to turbulent combustion.


Proceedings of the Combustion Institute2000-01-01+01:00; 33, pp 641-648 (2011) | 2011

Optical soot characterization using two-color laser-induced incandescence (2C-LII) in the soot growth region of a premixed flat flame

Henrik Bladh; Jonathan Johnsson; Nils-Erik Olofsson; Alexis Bohlin; Per-Erik Bengtsson


Proceedings of the Combustion Institute; 34, pp 3629-3636 (2013) | 2013

Pure rotational CARS measurements of temperature and O2-concentration in a low swirl turbulent premixed flame

Alexis Bohlin; Emil Nordström; Henning Carlsson; Xue-Song Bai; Per-Erik Bengtsson

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Brian D. Patterson

Sandia National Laboratories

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