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| 2. |
- Guo, Chen, et al.
(författare)
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Compact 200 kHz HHG source driven by a few-cycle OPCPA
- 2017
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Ingår i: The European Conference on Lasers and Electro-Optics, CLEO_Europe 2017. - 9781509067367 ; Part F82-CLEO_Europe 2017
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Konferensbidrag (refereegranskat)abstract
- We present a compact HHG source driven by a few-cycle, few μJ, 200 kHz OPCPA system. Efficient harmonics are generated from Neon, Argon and Krypton with conversion efficiency of 4.0×10-8, 1.2×10-6 and 4.1×10-6, respectively.
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| 3. |
- Johansson, Alexandra C., et al.
(författare)
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Faraday rotation spectroscopy using an optical frequency comb
- 2017
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Ingår i: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). - : IEEE. - 9781509067367
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Konferensbidrag (refereegranskat)abstract
- Summary form only given. The mid-infrared (MIR) part of the optical spectrum (3-12 μm) houses the fundamental absorption bands of a multitude of environmentally important molecules, but the abundance of water absorption often causes interference with the target species and makes concentration measurement inaccurate. The broad spectral coverage of optical frequency comb spectroscopy (OFCS) provides access to entire ro-vibrational bands and allows more accurate concentration quantification and retrieval of sample temperature. To further improve detection sensitivity of paramagnetic species in the presence of interfering species, we combine a MIR optical frequency comb with the Faraday rotation spectroscopy (FRS) technique [I], which is insensitive to interferences from diamagnetic molecules, such as H 2 O, CO 2 , and CO. In FRS, the rotation of the polarization induced by an external magnetic field in the vicinity of paramagnetic molecular transitions is translated to an intensity change by the use of a polarization analyzer, which effectively removes the influence of any non-paramagnetic species. In the proof of principle demonstration of OFC-FRS we detect nitric oxide (NO) in the presence of water at 5.3 μm using a Fourier transform spectrometer.
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| 4. |
- Khodabakhsh, Amir, et al.
(författare)
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Cavity-Enhanced Continuous-Filtering Vernier Spectroscopy at 3.3 mu m using a Femtosecond Optical Parametric Oscillator
- 2017
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Ingår i: 2017 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC). - : IEEE. - 9781509067367 ; , s. CH_2_2-
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Konferensbidrag (refereegranskat)abstract
- Optical frequency comb spectroscopy in the mid-infrared fingerprint region combines broad spectral bandwidth with high detection sensitivity and allows simultaneous detection of trace amounts of many molecular species. We have recently demonstrated a continuous-filtering Vernier spectrometer based on a mid-infrared optical frequency comb and an enhancement cavity for fast and sensitive detection of CH4 [1]. Here we present an improved, fully automatized and frequency calibrated continuous-filtering Vernier spectrometer, schematically shown in Fig. 1(a). The comb source is a doubly resonant optical parametric oscillator (DROPO) based on an orientation-patterned GaAs crystal synchronously pumped by a Tm:fiber femtosecond laser (125 MHz repetition rate, frep). The signal comb (3.1–3.4 µm, 30 mW) is mode matched to a 60-cm long Vernier enhancement cavity with a finesse of ~350 at 3.25 μm, placed in an enclosure that can be filled with the gas sample. The output mirror is attached to a PZT and mounted on a translation stage. When the cavity free spectral range is perfectly matched to twice the frep (250 MHz) every other signal comb mode is transmitted through the cavity. By detuning the cavity length from this perfect match position the cavity resonances act as a filter and transmit groups of comb modes called Vernier orders [2]. A diffraction grating mounted on a galvo-scanner separates these orders after the cavity and the chosen order is sent to the detection system. The Vernier order is tuned across the signal comb spectrum by scanning the cavity length (at 20 Hz) and the grating is rotated synchronously to fix the order in space and allow acquisition of the entire spectrum in 25 ms. Any residual mismatch between the cavity length scan and the grating rotation is compensated by a feedback loop acting on the frep of the pump laser and the PZT of the Vernier cavity [2]. A Fabry-Perot etalon is used for frequency calibration of the spectrometer. Figure 1(b) shows in black the normalized transmission spectrum of a sample containing 5.0 ppm CH4 and 160 ppm water. The red and blue curves show the corresponding fit of the Vernier spectrum [3] of CH4 and water, respectively, calculated using Voigt profiles, line parameters from the HITRAN database, and the experimentally determined cavity finesse. The figure of merit of the spectrometer is 1×10−9cm−1 Hz−1∕2 per spectral element and multiline fitting yields minimum detectable concentration of CH4 of 2 ppb in 25 ms, translating into 400 ppt Hz−1∕2 Since the spectrum of the signal comb covers the fundamental C-H stretch transitions we expect low detection limits for other hydrocarbons as well. In conclusion, mid-infrared comb-based continuous-filtering Vernier spectroscopy allows fast and highly sensitive measurement of broadband absorption spectra using a robust and compact detection system.
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| 5. |
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| 6. |
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| 7. |
- Major, B., et al.
(författare)
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Investigation of high harmonic generation using a high-power, 5-fs laser in a loose-focusing geometry
- 2017
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Ingår i: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). - : IEEE. - 9781509067367
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Konferensbidrag (refereegranskat)abstract
- Summary form only given. Since its first observation almost three decades ago high-order harmonic generation (HHG) in gases became a reliable source of extreme ultraviolet (XUV) pulses, which gave the possibility to study electronic processes on their natural timescale [1, 2]. While the main building blocks of the experimental setups for gas HHG are the same in almost all cases, the focusing or medium geometry varies from realization to realization based on, for example, the available laser power [3, 4].In this work we study HHG in a loose focusing geometry by focusing a ~50-mm diameter (FWHM) beam with a mirror of 16-m focal length (f-number ~320). The main subject of this analysis is to compare low pressure - long interaction length (few millibars and tens of centimeters) with high pressure - short medium (hundreds of millibars and a few millimeters) scenarios and understand the underlying reasons for the observed XUV radiation parameters. The experiments are carried out with on target 35 mJ, sub-5 fs, 740 nm central wavelength pulses provided by an optical parametric synthesizer [5], producing high-energy pulses at the 100 eV spectral region [6]. The theoretical analysis is performed by simulation code based on a three-dimensional nonadiabatic model [7,8]. The good agreement between the experimental and simulation data (see Fig. 1) allows us to use the theoretical findings to gain better insight on the exact phase-matching processes providing the observed features. This detailed description is used to draw general conclusions of the high-harmonic generation process.
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| 8. |
- Rutkowski, Lucile, et al.
(författare)
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Broadband and high resolution direct measurement of cavity resonances
- 2017
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Ingår i: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). - : IEEE. - 9781509067367
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Konferensbidrag (refereegranskat)abstract
- Summary form only given. Optical frequency combs offer unprecedented combination of broad bandwidth and high resolution and their coupling to enhancement cavities provides high sensitivity for spectroscopic measurements. Here we use a frequency-comb-based Fourier transform spectrometer (FTS) to measure the narrow resonances of a high-finesse cavity over a bandwidth of 100 nm around 1.55 μm and derive the group delay dispersion (GDD) of the cavity mirrors with precision below 1 fs 2 from the cavity resonance frequencies. We do this using a method that allows precise sampling of the comb intensities using an FTS with nominal resolution matched to the comb repetition rate (f rep ) [1, 2], and we demonstrate that sub-MHz resolution is achieved.
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| 9. |
- Rutkowski, Lucile, et al.
(författare)
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Detection of OH and H2O in an Atmospheric Flame by Near-Infrared Optical Frequency Comb Spectroscopy
- 2017
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Ingår i: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). - : IEEE. - 9781509067367
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Konferensbidrag (refereegranskat)abstract
- Absorption spectroscopy is attractive for combustion diagnostics because it allows in-situ and calibration-free quantification of reactants/products and thermometry. However, spectra measured at atmospheric pressure in the near-infrared telecom range, where laser sources and optical components are readily available, suffer from strong water interference. Cavity-enhanced optical frequency comb spectroscopy (CE-OFCS) is well suited for detection of other species, as it provides broad bandwidth with high signal-to-noise ratio and resolution, and allows de-convolving the spectra hidden among water transitions. Here we report detection of OH in the presence of H2O in an atmospheric premixed methane/air flat flame by CE-OFCS at 1.57 μm. We demonstrate a new water line list that is more accurate than HITEMP [1] and we isolate the OH lines by dividing spectra taken at different heights above the burner (HABs) to retrieve OH concentration and flame temperature.
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| 10. |
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| 11. |
- Silva, Francisco, et al.
(författare)
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Monolithic single-shot dispersion-scan : A new tool for real-time measurement and optimization of femtosecond pulses
- 2017
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Ingår i: The European Conference on Lasers and Electro-Optics, CLEO_Europe 2017. - 9781509067367
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Konferensbidrag (refereegranskat)abstract
- The precise characterization of femtosecond laser pulses is as challenging as their generation and a topic of intense research. Dispersion-scan (d-scan) [1] is a recently established technique where the spectrum of a nonlinear signal, e.g., second-harmonic generation (SHG), is measured as a function of dispersion applied to the pulse. The spectral phase of the pulse can then be retrieved from the resulting 2D trace using an iterative algorithm. An important implementation of d-scan, based on a chirped mirror and wedge compressor, involves progressively moving one of the wedges around the maximum compression point and acquiring the resulting SHG spectrum for each insertion with a standard spectrometer. This robust and fully inline approach, which does not require any beamsplitting or temporal delays, has enabled the simultaneous compression and measurement of pulses down to single-cycle durations [2-4], but its scanning nature precludes single-shot operation. A single-shot d-scan variant that explores the spatially dependent dispersion of a glass prism was successfully demonstrated with 3.2 fs pulses [5], but the relatively small amount of dispersion that can be introduced by a single prism limits its use to few-cycle pulses.
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| 12. |
- Soboń, Grzegorz, et al.
(författare)
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High-power broadband source tunable from 2.8 to 4 μm based on difference frequency generation
- 2017
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Ingår i: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). - : IEEE. - 9781509067367
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Konferensbidrag (refereegranskat)abstract
- Mid-infrared (MIR) frequency comb sources enable high-speed and accurate detection of various species, since many molecules possess their fingerprints in this wavelength range. Usually, broadband radiation in this spectral region is obtained from optical parametric oscillators (OPOs), which provide high output power and broad tuning capabilities [1]. However, OPO sources require locking of the cavity to the pumping oscillator, which increases the complexity. MIR sources based on difference frequency generation (DFG) are interesting alternatives to OPOs, due to their simplicity, single-pass configuration, broad tunability, and fully passive cancellation of the carrier-envelope offset in the generated idler pulses. However, the conversion efficiency of the DFG process is usually insufficient to reach the output power levels easily achieved in OPO systems. Here, we demonstrate a widely tunable DFG source based on a mode-locked Yb-doped fiber laser, with average MIR output power reaching 165 mW, which is more than in previous reports on similar DFG systems [2,3].
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| 13. |
- Tsatrafyllis, N., et al.
(författare)
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The ion microscope as a tool for imaging the ion distribution produced by linear and non-linear processes at the focus of an XUV beam
- 2017
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Ingår i: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). - : IEEE. - 9781509067367
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Konferensbidrag (refereegranskat)abstract
- Summary form only given. We demonstrate a tool for quantitative measurements in the linear and non-linear extreme ultraviolet (XUV) spectral region measuring spatially resolved atomic ionization products at the focus of an XUV beam [1, 2]. The ionizing radiation is a comb of the 11th-15th harmonics of a Ti:Sapphire femtosecond laser beam produced in a Xenon gas jet. The spatial ion distribution at the focus of the harmonics is recorded using an ion microscope detector [2, 3]. Spatially resolved single- and two-photon ionization products of Argon and Helium are observed. From such ion distributions single- and two-photon generalized cross sections have be extracted by a self-calibrating method. This is the first observation of spatially resolved two-XUV-photon ionization at the focus of the XUV radiation which constitutes an important step towards future single-shot temporal characterization of attosecond (asec) pulses [4].
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| 14. |
- Wolf, T. J. A., et al.
(författare)
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Probing molecular photoinduced dynamics by ultrafast soft x-rays
- 2017
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Ingår i: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). 25-29 June 2017, Munich, Germany. - : IEEE. - 9781509067367 - 9781509067374
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Konferensbidrag (refereegranskat)abstract
- Summary form only given. Molecules selectively transform light energy from the sun into other forms of energy like heat, electricity, or chemical energy with high quantum efficiency. The energy conversion process is the result of a correlated motion of electrons and nuclei after photoexcitation, often under breakdown of the Born-Oppenheimer approximation. The element and site selectivity of x-rays allows observing molecular processes from a different point of view compared to ultrafast optical probes [1,2]. I will concentrate on time resolved x-ray absorption spectroscopy. The method provides high selectivity on the transient electronic structure of a molecule. Recently, we establishes this method in the soft x-ray domain for probing ππ* to nπ* transitions, a general and important process for molecular energy conversion. Fig. 1 shows a sketch of thymine, used in the experiment, with one of the oxygen 1s core orbitals and the π,n and π* valence orbitals. While valence orbitals are generally delocalized over the whole molecular body, the lone pair n orbital is essentially an oxygen 2p orbital. An x-ray induced transition from the oxygen 1s to the n orbital will result in a strong absorption maximum in the pre-edge region. We use this feature to probe the molecular dynamics after photoexcitation.
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