Spatially resolved measurements of the magnetization dynamics on a thin CoFeB film induced by an intense laser pump-pulse reveal that the frequencies of resulting spin-wave modes depend strongly on the distance to the pump center. This can be attributed to a laser generated temperature profile. We determine a shift of 0.5 GHz in the spin-wave frequency due to the spatial thermal profile induced by the femtosecond pump pulse that persists for up to one nanosecond. Similar experiments are presented for a magnonic crystal composed of a CoFeB-film based antidot lattice with a Damon Eshbach mode at the Brillouin zone boundary and its consequences are discussed.
In order to utilize the high repetition rates now available at X-ray free-electron laser sources for serial crystallography, methods must be developed to softly deliver large numbers of individual microcrystals at high repetition rates and high speeds. Picosecond infrared laser (PIRL) pulses, operating under desorption by impulsive vibrational excitation (DIVE) conditions, selectively excite the OH vibrational stretch of water to directly propel the excited volume at high speed with minimized heating effects, nucleation formation or cavitationinduced shock waves, leaving the analytes intact and undamaged. The soft nature and laser-based sampling flexibility provided by the technique make the PIRL system an interesting crystal delivery approach for serial crystallography. This paper demonstrates that protein crystals extracted directly from aqueous buffer solution via PIRL-DIVE ablation retain their diffractive properties and can be usefully exploited for structure determination at synchrotron sources. The remaining steps to implement the technology for high-speed serial femtosecond crystallography, such as single-crystal localization, high-speed sampling and synchronization, are described. This proof-of-principle experiment demonstrates the viability of a new laser-based high-speed crystal delivery system without the need for liquid-jet injectors or fixed-target mounting solutions
The benzyltriphenylphosphonium (BTP) thermometer ion is utilized to characterize the fragmentation mechanisms of matrix-assisted laser desorption/ionization (MALDI) for femtosecond ultraviolet laser pulses. We demonstrate that the survival yield of BTP approaches unity under these conditions, which suggests that a minimal amount of fragmentation is occurring. It is also shown that the survival yield of BTP is insensitive to the laser fluence. However, the magnitude of fragmentation for the matrix increased notably for the same fluence range. These results indicate that the amount of energy transferred from the matrix ions to the BTP thermometer ions is minimal because the femtosecond desorption applied here occur within the stress-confinement regime. This observation is in agreement with recent molecular dynamics simulations which predict that it should be possible to separate both desorption and ionization processes in the regime of stress-confined desorption. Our results indicate that angiotensin is the largest biomolecule which could be routinely measured with these pulses. A mass upper-limit supports the hypothesis that ionization is hindered by the increased thermal gradients imposed in the lattice and associated velocity distribution within the ablation process from the much higher lattice heating rate with femtosecond pulses. This effect results in the temporal overlap between the neutral molecules and the matrix ions being too small to result in sufficient proton exchange for ionization. Graphical TOC Entry2
Material ablation and evaporation using pulsed infrared lasers pose promising approaches for matrix-free laser desorption ionization and in laser surgery. For the best results, key parameters such as laser wavelength, pulse duration, and pulse energy need to be carefully adjusted to the application. We characterize the dynamics at the water-air interface induced by a 10 ps infrared laser tuned to the water absorption band at 3 lm, a parameter set facilitating stress confined desorption for typical absorption depths in biological samples and tissue. By driving the ablation faster than nucleation growth, cavitation induced sample damage during the ablation process can be mitigated. The resultant explosive ablation process leads to a shock front expansion and material ejection which we capture using off-axis digital interference microscopy, an interference technique particularly useful for detecting the phase shift caused by transparent objects. It is demonstrated that the method can yield local density information of the observed shock front with a single image acquisition as compared to the usually performed fit of the velocity extracted from several consecutive snapshots. We determine the ablation threshold to be ð0:560:2Þ J cm À2 and observe a significant distortion of the central parts of the primary shock wave above approximately 2:5 J cm À2. The differences in plume shape observed for higher fluences are reflected in an analysis based on shock wave theory, which shows a very fast initial expansion.
The fragmentation mechanisms of matrix-assisted laser desorption/ionization (MALDI) for femtosecond ultraviolet laser pulses in a transmission geometry are characterized on the basis of the well-known benzyltriphenylphosphonium (BTP) thermometer ion. We demonstrate that the survival yield of BTP approaches unity under these conditions, which suggests that a minimal amount of fragmentation is occurring. It is shown that, while the survival yield of BTP is insensitive to the fluence within the studied fluence range, the magnitude of fragmentation for the matrix increased notably with increasing fluence. While nonlinear absorption and ionization are expected to lead to large matrix fragmentation rates, the high BTP survival yields indicate a reduced amount of energy being transferred from the matrix to these BTP thermometer ions. The femtosecond ablation employed here results in increased heating rates and occurs within the fully stress-confinement regime, which minimizes the matrix-analyte interaction during the ablation event. This interpretation is supported by our finding that angiotensin was the largest biomolecule which could be routinely be measured with femtosecond pulses. The spatio-temporal overlap between a neutral biomolecule and matrix ions resulting from this process is too short to result in sufficient proton exchange for ionization.<br>
The fragmentation mechanisms of matrix-assisted laser desorption/ionization (MALDI) for femtosecond ultraviolet laser pulses in a transmission geometry are characterized on the basis of the well-known benzyltriphenylphosphonium (BTP) thermometer ion. We demonstrate that the survival yield of BTP approaches unity under these conditions, which suggests that a minimal amount of fragmentation is occurring. It is shown that, while the survival yield of BTP is insensitive to the fluence within the studied fluence range, the magnitude of fragmentation for the matrix increased notably with increasing fluence. While nonlinear absorption and ionization are expected to lead to large matrix fragmentation rates, the high BTP survival yields indicate a reduced amount of energy being transferred from the matrix to these BTP thermometer ions. The femtosecond ablation employed here results in increased heating rates and occurs within the fully stress-confinement regime, which minimizes the matrix-analyte interaction during the ablation event. This interpretation is supported by our finding that angiotensin was the largest biomolecule which could be routinely be measured with femtosecond pulses. The spatio-temporal overlap between a neutral biomolecule and matrix ions resulting from this process is too short to result in sufficient proton exchange for ionization.<br>
We present a cryogenic mass spectrometry protocol with the capability to detect peptides in the attomole dilution range from ice films. Our approach employs femtosecond laser pulses and implements neither substrate modification nor proton donor agents in the aqueous solution, known to facilitate analyte detection in mass spectrometry. In a systematic study, we investigated the impact of temperature, substrate composition, and irradiation wavelength (513 and 1026 nm) on the bradykinin signal onset. Our findings show that substrate choice and irradiation wavelength have a minor impact on signal intensity once the preparation protocol is optimized. However, if the temperature is increased from −140 to 0 °C, which is accompanied by ice film thinning, a somehow complex picture of analyte desorption and ionization is recognizable, which has not been described in the literature yet. Under cryogenic conditions (−140 °C), obtaining a signal is only possible from isolated sweet spots across the film. If the thin ice film is between −100 and −70 °C of temperature, these sweet spots appear more frequently. Ice sublimation triggered by temperatures above −70 °C leads to an intense and robust signal onset that could be maintained for several hours. In addition to the above findings, we notice that a vibrant fragmentation pattern produced is strikingly similar with both wavelengths. Our findings suggest that while following an optimized protocol, femtosecond mass spectrometry has excellent potential to analyze small organic molecules and peptides with a mass range of up to 2.5 kDa in aqueous solution without any matrix, as employed in matrix-assisted laser desorption/ionization (MALDI) or any substrate surface modification, found in surface-assisted laser desorption/ionization (SALDI).
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