Name: direct imaging of laser-driven ultrafast molecular rotation
Uploaded: 2017-02-04T13:00:00.000+00:00
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Description: Watch this Scientific Journal Video about Direct Imaging of Laser-driven Ultrafast Molecular Rotation at JoVE.com

This work was supported in part by grants-in-aid KAKENHI from the Japan Society for the Promotion of Science (JSPS) and the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) Japan (#26104539, #26620020, #26810011, #15H03766, #15KT0060, #16H00826, and #16K13927); the Konica Minolta Science and Technology Foundation; the "Planting Seeds for Research" program of TokyoTech; the Imaging Science Project of the Center for Novel Science Initiatives (CNSI) at the National Institutes of Natural Sciences (NINS) (#IS261006); the RIKEN-IMS joint program on "Extreme Photonics;" and the Consortium for Photon Science and Technology (CPhoST).

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The authors have nothing to disclose.

Il presente procedimento permette di acquisire un filmato in tempo reale della rotazione molecolare con una configurazione di immagini 2D fessura base. Poiché gli ioni osservate passano attraverso la fessura, passo 1.5 è una delle fasi critiche. I bordi delle lame a fessura devono essere taglienti. Quando c&#39;è un piccolo difetto, come un dente 0,3 mm fessura, un graffio si osserva l&#39;immagine ioni nella (Figura 6). In tal caso, la lama a fessura deve essere lucidato con 2.000-grana carta vetrat...

Per una comprensione e una migliore utilizzazione della natura dinamica delle molecole, è essenziale visualizzare chiaramente movimenti molecolari di interesse. L&#39;imaging esplosione Coulomb tempo risolto è uno dei potenti approcci per raggiungere questo obiettivo 1, 2, 3. In questo approccio, le dinamiche molecolari di interesse vengono avviate da un campo laser di pompa ultracorti e vengono sondati da un impulso probe ritardata. Su sonda irraggiamento, molecole ionizzate moltiplicano e suddivisi in frammenti ionici causa della repulsione coulombiana. La distribuzione spaziale degli ioni espulsi è una misura della struttura molecolare e l&#39;orientamento spaziale a irradiazione sonda. Una sequenza di misurazione scansione del tempo di ritardo pump-probe porta alla creazione di un film molecolare. È interessante notare che, per il caso più semplice - molecole biatomiche - distribuzione angolare degli ioni espulsiriflette direttamente la distribuzione dell&#39;asse molecolare (cioè, la funzione d&#39;onda rotazionale quadrato). Per quanto riguarda il processo di pompa, recenti progressi nel controllo coerente del moto molecolare utilizzando campi laser ultracorti ha portato alla creazione di pacchetti d&#39;onda rotazione altamente controllate 4, 5. Inoltre, la direzione di rotazione può essere controllato attivamente utilizzando un campo di polarizzazione controllato laser 6, 7, 8. È stato quindi previsto che un quadro dettagliato di rotazione molecolare, compreso nature onda, potrebbe essere visualizzato quando la tecnica di imaging esplosione coulombiana è combinata con un tale processo pompa 9, 10, 11, 12, 13. Tuttavia, abbiamo alcunivolte incontrano difficoltà sperimentali associati ai metodi di imaging esistenti, come indicato di seguito. Lo scopo di questo lavoro è quello di presentare un nuovo modo di superare queste difficoltà e di creazione di un filmato di alta qualità di pacchetti d&#39;onda di rotazione molecolare. Il primo film sperimentale di rotazione molecolare presa con il presente metodo, insieme con le sue implicazioni fisiche, sono stati presentati nella precedente carta 11. Lo sfondo dello sviluppo, l&#39;aspetto teorico dettagliata della attuale tecnica di imaging, e il confronto con altre tecniche esistenti saranno date in un prossimo documento. Qui, ci si concentrerà principalmente sugli aspetti pratici e tecnici della procedura, compresa la combinazione della configurazione ottica tipica pump-probe e il nuovo apparato di immagini. Come nel precedente lavoro, il sistema di destinazione è unidirezionale rotazione molecole di azoto 11. La principale difficoltà sperimentale dellaconfigurazione di imaging, schematicamente illustrato in figura 1 esistente, ha a che fare con la posizione del rilevatore, o l&#39;angolo della telecamera. Poiché l&#39;asse di rotazione coincide con la propagazione laser all&#39;asse 6, 7, 8 in rotazione molecolare laser-indotta dal campo, non è pratico installare un rilevatore lungo l&#39;asse di rotazione. Quando il rivelatore è installato in modo da evitare l&#39;irradiazione laser, l&#39;angolo della telecamera corrisponde a un&#39;osservazione lato di rotazione. In questo caso, non è possibile ricostruire l&#39;orientamento originale molecole dall&#39;immagine proiettata (2D) ione 14. Un imaging 3D rilevatore 14, 15, 16, 17, 18, 19, con la quale il tempo di arrivo al rivelatore superiore e IMPAC ioneposizioni t possono essere misurati, ha offerto un modo unico per osservare direttamente la rotazione molecolare utilizzando Coulomb esplosione di imaging 10, 12. Tuttavia, i conteggi di ioni accettabili per colpo laser sono basse (tipicamente &lt;10 ioni) nel rivelatore 3D, che significa che è difficile creare un film lungo di moto molecolare con alta qualità di immagine 14. Il tempo morto dei rivelatori (tipicamente NS) colpisce anche la risoluzione dell&#39;immagine e l&#39;efficienza di imaging. Inoltre non è un compito semplice per fare un buon pump-probe sovrapposizione fascio di ioni attraverso il monitoraggio immagine in tempo reale con una frequenza di ripetizione del laser di &lt;~ 1 kHz. Anche se diversi gruppi hanno osservato pacchetti d&#39;onda di rotazione con la tecnica 3D, le informazioni spaziali è stato limitato e / o diretta, e una visualizzazione dettagliata di onda della natura, comprese le strutture nodali complicate, non è stato raggiunto il 10, 12. L&#39;essenzala nuova tecnica di imaging è l&#39;uso della &quot;nuova angolazione&quot; in Figura 1. In questa configurazione, l&#39;esposizione del fascio laser per un rivelatore è evitata mentre il rilevatore 2D è parallelo al piano di rotazione, portando all&#39;osservazione dalla direzione dell&#39;asse di rotazione. La fessura consente solo lo ione nel piano di rotazione (il piano di polarizzazione degli impulsi laser) per contribuire a un&#39;immagine. Un rivelatore 2D, che offre una velocità di conteggio più alto (tipicamente ~ 100 ioni) di un rivelatore 3D, può essere utilizzato. La configurazione dell&#39;elettronica è più semplice rispetto al caso di rilevamento 3D, mentre l&#39;efficienza di misurazione è maggiore. In termini di tempo di ricostruzione matematica, come Abel inversione 14, inoltre, non è necessario per estrarre le informazioni angolare. Queste caratteristiche portano alla semplice ottimizzazione del sistema di misura e alla produzione di film di alta qualità. Un apparato di immagini di particelle cariche serie 2D / 3D può essere facilmente modificato per la presente witho configurazioneut l&#39;uso di apparecchiature costose.

<table><tbody><tr><td>CMOS camera</td><td>Toshiba TELI</td><td>BU-238M-ES</td><td>equipped with SONY IMX174 sensor</td></tr><tr><td>High voltage switch</td><td>Behlke</td><td>HTS-41-03-GSM</td><td></td></tr><tr><td>High voltage switch</td><td>Behlke</td><td>HTS-80-03</td><td></td></tr><tr><td>Digital delay generator</td><td>Stanford research systems</td><td>DG535</td><td></td></tr><tr><td>Digital delay generator</td><td>Stanford research systems</td><td>DG645</td><td></td></tr><tr><td>Microchannel plate</td><td>Photonis</td><td>3075</td><td></td></tr><tr><td>Pulsed valve</td><td>LAMID LTD</td><td>Even-Lavie valve&amp;nbsp;</td><td>High repetition, room temperature model</td></tr><tr><td>Molecular beam skimmers</td><td>Institute for Molecular Science</td><td>13C11</td><td>3 and 1.5 mm center hole, 25 degrees full inner angle, and ~50 mm length</td></tr><tr><td>Optical Comparator</td><td>Nikon</td><td>V-24B</td><td></td></tr><tr><td>DPSS laser</td><td>Lighthouse Photonics</td><td>Sprout</td><td></td></tr><tr><td>Femtosecond Ti:Sapphire oscillator</td><td>KMLabs</td><td>Halcyon</td><td></td></tr><tr><td>Femtosecond Ti:Sapphire amplifier</td><td>Quantronix</td><td>Odin-II HE</td><td></td></tr><tr><td>Motorized linear stage</td><td>Sigma Koki</td><td>KST(GS)-100X</td><td></td></tr><tr><td>Manual X-stage</td><td>Sigma Koki</td><td>TSD-601S</td><td></td></tr><tr><td>High resolution mirror mount</td><td>Newport</td><td>Suprema SX100-F2KN-254</td><td></td></tr><tr><td>High resolution mirror mount</td><td>LIOP-TEC GmbH</td><td>SR100-100R-2-HS</td><td></td></tr><tr><td>Polarization checker</td><td>Paradigm Devices, Inc.</td><td>O-tool VIS</td><td></td></tr><tr><td>Instrument communication interface</td><td>National Instruments</td><td>NI-MAX</td><td></td></tr><tr><td>Graphical development environment for measurement programs</td><td>National Instruments</td><td>LabVIEW 2014</td><td></td></tr><tr><td>Laser line dielectric mirror</td><td>CVI/LEO</td><td>TLM2-400/800-45UNP</td><td></td></tr><tr><td>Laser line dielectric mirror</td><td>Altechna</td><td>Low GDD Ultrafast mirror</td><td></td></tr><tr><td>Laser line dielectric mirror</td><td>Altechna</td><td>Low GDD Ultrafast mirror</td><td></td></tr><tr><td>Femtosecond polarizer</td><td>Advanced Thin Films</td><td>PBS-GVD</td><td></td></tr></tbody></table>

direct imaging of laser-driven ultrafast molecular rotation

Vi presentiamo un metodo per la visualizzazione ultraveloci molecolari dinamiche pacchetto onda rotazione laser-indotta,. Abbiamo sviluppato una nuova impostazione di imaging esplosione 2-dimensionale Coulomb, in cui si realizza un angolo di ripresa fino a quel momento, impraticabile. Nella nostra tecnica di imaging, molecole biatomiche sono irradiati con un forte impulso laser polarizzata circolarmente. Gli ioni atomici espulsi vengono accelerati perpendicolarmente alla propagazione laser. Gli ioni giacenti nel piano di polarizzazione laser vengono selezionati attraverso l&#39;uso di una fenditura meccanica e ripreso con un alto rendimento, rivelatore 2-dimensional installato parallelo al piano di polarizzazione. Poiché un circolarmente polarizzata (isotropo) Coulomb impulso esplodere viene utilizzato, la distribuzione angolare osservata degli ioni espulsi corrisponde direttamente alla funzione d&#39;onda quadrata rotazione al momento della irradiazione impulsi. Per creare un filmato in tempo reale della rotazione molecolare, la presente tecnica di imaging è combinato con una pompa-probe a femtosecondi oconfigurazione ptical in cui gli impulsi di pompa create unidirezionalmente rotazione formazioni molecolari. A causa della elevata produttività immagine del nostro sistema di rilevamento, la condizione sperimentale pompa-sonda può essere facilmente ottimizzato controllando un&#39;istantanea in tempo reale. Come risultato, la qualità del filmato osservata è sufficientemente elevata per visualizzare la natura ondulatoria dettagliata del moto. Si segnala altresì che l&#39;attuale tecnica può essere implementato in configurazioni esistenti imaging standard ionici, offrendo una nuova angolazione o punto di vista dei sistemi molecolari senza necessità di modifica estesa.

La figura 4A mostra una sonda di sola immagine raw della N 2+ ioni espulso su sonda irradiazione (esplosione Coulomb), preso per il colpo del laser una sonda. Ogni punto luminoso corrisponde ad uno ione. La figura 4B mostra un&#39;immagine riassunto di 10.000 immagini Camera RAW binarizzate. Queste immagini dimostrano che la nostra configurazione di imaging può monitorare le molecole di tutti gli angoli di orientamento del piano di pol...

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Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

Direct Imaging di laser-driven ultraveloce rotazione molecolare

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

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Chemistry

Chemical Bonding: Molecular Geometry and Bonding Theories

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9.7K Views.  Tokyo Institute of Technology. We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

Video: Direct Imaging of Laser-driven Ultrafast Molecular Rotation

Fluorescence Lifetime Imaging of Molecular Rotors in Living Cells

Diffusion is often an important rate-determining step in chemical reactions or biological processes and plays a role in a wide range of intracellular events. Viscosity is one of the key parameters affecting the diffusion of molecules and proteins, and changes in viscosity have been linked to disease and malfunction at the cellular level.1-3 While methods to measure the bulk viscosity are well developed, imaging microviscosity remains a challenge. Viscosity maps of microscopic objects, such as single cells, have until recently been hard to obtain. Mapping viscosity with fluorescence techniques is advantageous because, similar to other optical techniques, it is minimally invasive, non-destructive and can be applied to living cells and tissues.
Fluorescent molecular rotors exhibit fluorescence lifetimes and quantum yields which are a function of the viscosity of their microenvironment.4,5 Intramolecular twisting or rotation leads to non-radiative decay from the excited state back to the ground state. A viscous environment slows this rotation or twisting, restricting access to this non-radiative decay pathway. This leads to an increase in the fluorescence quantum yield and the fluorescence lifetime. Fluorescence Lifetime Imaging (FLIM) of modified hydrophobic BODIPY dyes that act as fluorescent molecular rotors show that the fluorescence lifetime of these probes is a function of the microviscosity of their environment.6-8 A logarithmic plot of the fluorescence lifetime versus the solvent viscosity yields a straight line that obeys the F&ouml;rster Hoffman equation.9 This plot also serves as a calibration graph to convert fluorescence lifetime into viscosity.
Following incubation of living cells with the modified BODIPY fluorescent molecular rotor, a punctate dye distribution is observed in the fluorescence images. The viscosity value obtained in the puncta in live cells is around 100 times higher than that of water and of cellular cytoplasm.6,7 Time-resolved fluorescence anisotropy measurements yield rotational correlation times in agreement with these large microviscosity values. Mapping the fluorescence lifetime is independent of the fluorescence intensity, and thus allows the separation of probe concentration and viscosity effects. 
In summary, we have developed a practical and versatile approach to map the microviscosity in cells based on FLIM of fluorescent molecular rotors.

Fluorescence Lifetime Imaging (FLIM) has emerged as a key technique to image the environment and interaction of specific proteins and dyes in living cells. FLIM of fluorescent molecular rotors allows mapping of viscosity in living cells.

Lifetime Imaging di fluorescenza di rotori molecolari nelle cellule viventi

Diffusion is often an important rate-determining step in chemical reactions or biological processes and plays a role in a wide range of intracellular ...

Ricerca

Bioingegneria

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

Separazione spaziale di conformatori molecolari e cluster

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Ingegneria

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is &#177; 5 parts in 107. Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH2F2, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO2 pump laser, and strength.

We describe the generation of far-infrared radiation using an optically pumped molecular laser along with the measurement of their frequencies with heterodyne techniques. The experimental system and techniques are demonstrated using difluoromethane (CH2F2) as the laser medium whose results include three new laser emissions and eight measured laser frequencies.

Caratterizzare lontano infrarosso Emissioni laser e la misurazione delle loro frequenze

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and ...

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

This article shows how the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) or the "reaction microscope" technique can be used to distinguish between enantiomers (stereoisomers) of simple chiral species on the level of individual molecules. In this approach, a gaseous molecular jet of the sample expands into a vacuum chamber and intersects with femtosecond (fs) laser pulses. The high intensity of the pulses leads to fast multiple ionization, igniting a so-called Coulomb Explosion that produces several cationic (positively charged) fragments. An electrostatic field guides these cations onto time- and position-sensitive detectors. Similar to a time-of-flight mass spectrometer, the arrival time of each ion yields information on its mass. As a surplus, the electrostatic field is adjusted in a way that the emission direction and the kinetic energy after fragmentation lead to variations in the time-of-flight and in the impact position on the detector.
Each ion impact creates an electronic signal in the detector; this signal is treated by high-frequency electronics and recorded event by event by a computer. The registered data correspond to the impact times and positions. With these data, the energy and the emission direction of each fragment can be calculated. These values are related to structural properties of the molecule under investigation, i.e. to the bond lengths and relative positions of the atoms, allowing to determine molecule by molecule the handedness of simple chiral species and other isomeric features.

For small chiral species, Coulomb Explosion Imaging provides a new approach to determine the handedness of individual molecules.

Formazione immagine di esplosione Coulombiana come uno strumento per distinguere tra stereoisomeri

This article shows how the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) or the "reaction microscope" technique can be used to distinguish ...

Chimica

Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs the anharmonicity of the ODT, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, we selectively excite the hotter atoms out of the trap while keeping the colder atoms in the trap, generating parametric cooling. This experimental protocol starts with a magneto-optical trap (MOT) that is loaded by a Zeeman slower. The precooled atoms in the MOT are then transferred to an ODT, and a bias magnetic field is applied to create an interacting Fermi gas. We then lower the trapping potential to prepare a cold Fermi gas near the degenerate temperature. After that, we sweep the magnetic field to the noninteracting regime of the Fermi gas, in which the parametric cooling can be manifested by modulating the intensity of the optical trapping beams. We find that the parametric cooling effect strongly depends on the modulation frequencies and amplitudes. With the optimized frequency and amplitude, we measure the dependence of the cloud energy on the modulation time. We observe that the cloud energy is changed in an anisotropic way, where the energy of the axial direction is significantly reduced by parametric driving. The cooling effect is limited to the axial direction because the dominant anharmonicity of the crossed-beam ODT is along the axial direction. Finally, we propose to extend this protocol for the trapping potentials of large anharmonicity in all directions, which provides a promising scheme for cooling quantum gases using external driving.

We present a parametric driving method to cool an ultracold Fermi gas in a crossed-beam optical dipole trap. This method selectively removes high-energy atoms from the trap by periodically modulating the trap depth with frequencies that are resonant with the anharmonic components of the trapping potential.

Raffreddamento un otticamente Intrappolato ultrafreddi Fermi gas da guida periodica

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

Nuove tecniche per l'osservazione dinamica strutturale dei cristalli liquidi fotoresponsivi

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the wavelength of the strong-field ionizing pump pulse from the commonly used 800 nm into the near-infrared (1200-1600 nm), the contribution of adiabatic electron tunneling to the ionization process increases relative to multiphoton absorption. Adiabatic ionization results in predominant population of the ground electronic state of the ion upon electron removal, which effectively prepares a coherent vibrational state (&#34;wave packet&#34;) amenable to subsequent excitation. In our experiments, the coherent vibrational dynamics are probed with a weak-field 800 nm pulse and the time-dependent yields of dissociation products measured in a time-of-flight mass spectrometer. We present the measurements on the molecule dimethyl methylphosphonate (DMMP) to illustrate how using 1500 nm pulses for excitation enhances the amplitude of coherent oscillations in ion yields by a factor of 10 as compared to 800 nm pulses. This protocol may be implemented in existing pump-probe setups through the incorporation of an optical parametric amplifier (OPA) for wavelength conversion.

We present a protocol for probing ultrafast vibrational coherences in polyatomic radical cations that result in molecular dissociation.

Misurazione di coerenze ultraveloce vibrazionale in cationi poliatomici radicale con ionizzazione adiabatico del forte-campo

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the ...

Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.

Plasmonic gold nanorods can be trapped in liquids and rotated at kHz frequencies using circularly-polarized optical tweezers. Introducing tools for Brownian dynamics analysis and light scatteringspectroscopy leads to a powerful system for research and application in numerous fields of science.

Costruzione e funzionamento di un sistema motore basato su luce oro Nanorod Rotary

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and ...

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

The design and synthesis of a synthetic system that aims for the direct visualization of a synthetic rotary motor at the single molecule level on surfaces are demonstrated. This work requires careful design, considerable synthetic effort, and proper analysis. The rotary motion of the molecular motor in solution is shown by 1H NMR and UV-vis absorption spectroscopy techniques. In addition, the method to graft the motor onto an amine-coated quartz is described. This method helps to gain more insight into molecular machines.

The manuscript describes how to synthesize and graft a molecular motor on surfaces for single molecular imaging.

Motori molecolari basati su luce sulle superfici per l'Imaging molecolare singola

The design and synthesis of a synthetic system that aims for the direct visualization of a synthetic rotary motor at the single molecule level on surfaces ...

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species in the ppm-to-single-percent range. The main purpose of the method is the spatially resolved detection of low-concentration species, which have no transitions in the visible or near-IR spectral range that could be used for detection. IR-DFWM is a nonintrusive method, which is a great advantage in combustion research, as inserting a probe into a flame can change it drastically. The IR-DFWM is combined with upconversion detection. This detection scheme uses sum-frequency generation to move the IR-DFWM signal from the mid-IR to the near-IR region, to take advantage of the superior noise characteristics of silicon-based detectors. This process also rejects most of the thermal background radiation. The focus of the protocol presented here is on the proper alignment of the IR-DFWM optics and on how to align an intracavity upconversion detection system.

Here, we present a protocol to perform sensitive, spatially resolved gas spectroscopy in the mid-infrared region, using degenerate four-wave mixing combined with upconversion detection.

A raggi infrarossi degenerato quattro-onda miscelazione con rilevamento di Upconversion per sensoristica quantitativa

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species ...