Rydberg state dynamics and fragmentation mechanism of N,N,N',N'-tetramethylmethylenediamine.

The non-adiabatic relaxation processes and the fragmentation dynamics of Rydberg-excited N,N,N',N'-tetramethylmethylenediamine (TMMDA) are investigated using femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. Excitation at 208 nm populates TMMDA in a charge-localized 3p state. Rapid internal conversion (IC) to 3s produces two charge-delocalized conformers with independent time constants and distinct population ratios.

Structural dynamics upon photoinduced charge transfer in N,N,N',N'-tetramethylmethylenediamine.

The ultrafast structural motion linked to the charge transfer process in Rydberg excited N,N,N',N'-tetramethylmethylenediamine (TMMDA) has been monitored in real time using femtosecond time-resolved photoelectron imaging coupled with quantum chemical calculations. Optical excitation to the 3 s Rydberg state initially populates the charge on one of the two amine groups, resulting in a charge-localized structure in the Franck-Condon (FC) region. As the wavepacket evolves on the 3 s potential surface, the molecular geometry changes with time, leading to the corresponding variation in the charge distribution.

Intersystem Crossing of 2-Methlypyrazine Studied by Femtosecond Photoelectron Imaging.

2-methylpyrazine was excited to the high vibrational dynamics of the S state with 260 nm femtosecond laser light, and the evolution of the excited state was probed with 400 nm light. Because it was unstable, the S state decayed via intersystem crossing to the triplet state T, and it may have decayed to the ground state S via internal conversion. S-to-T intersystem crossing was observed by combining time-resolved mass spectrometry and time-resolved photoelectron spectroscopy.

Two-watt mid-infrared laser emission in robust fluorozirconate fibers.

To the best of our knowledge, we report here the first demonstration of 2.9 µm laser emission from in-house fabricated Ho/Pr co-doped ZBYA glass fiber. The fiber was fabricated based on the ZBYA glass with compositions of ZrF-BaF-YF-AlF-PbF-HoF-PrF.

Strain-, curvature- and twist-independent temperature sensor based on a small air core hollow core fiber structure.

Cross-sensitivity (crosstalk) to multiple parameters is a serious but common issue for most sensors and can significantly decrease the usefulness and detection accuracy of sensors. In this work, a high sensitivity temperature sensor based on a small air core (10 µm) hollow core fiber (SACHCF) structure is proposed. Co-excitation of both anti-resonant reflecting optical waveguide (ARROW) and Mach-Zehnder interferometer (MZI) guiding mechanisms in transmission are demonstrated.

Negative Curvature Hollow Core Fiber Based All-Fiber Interferometer and Its Sensing Applications to Temperature and Strain.

Negative curvature hollow core fiber (NCHCF) is a promising candidate for sensing applications; however, research on NCHCF based fiber sensors starts only in the recent two years. In this work, an all-fiber interferometer based on an NCHCF structure is proposed for the first time. The interferometer was fabricated by simple fusion splicing of a short section of an NCHCF between two singlemode fibers (SMFs).

Strain independent twist sensor based on uneven platinum coated hollow core fiber structure.

Optical fiber based twist sensors usually suffer from high cross sensitivity to strain. Here we report a strain independent twist sensor based on an uneven platinum coated hollow core fiber (HCF) structure. The sensor is fabricated by splicing a section of ~4.

Femtosecond real-time probing of the excited-state intramolecular proton transfer reaction in methyl salicylate.

The excited-state intramolecular proton transfer (ESIPT) process and subsequent electronic relaxation dynamics in methyl salicylate have been investigated using femtosecond time-resolved ion yield spectroscopy combined with time-resolved photoelectron imaging. Excitation with a tunable pump pulse populates the keto tautomer in the first excited electronic state S(ππ). As a hydrogen atom transfers from the phenolic group to the carbonyl group within 100 fs, the molecular geometry changes gradually, leading to a variation in the electronic photoionization channel.

Sub-micrometer resolution liquid level sensor based on a hollow core fiber structure.

Liquid level measurement in lab on a chip (LOC) devices is a challenging task due to the demand for a sensor with ultra-high resolution but miniature in nature. In this Letter, we report a simple, compact in size, yet highly sensitive liquid level sensor based on a hollow core fiber (HCF) structure. The sensor is fabricated by fusion splicing a short section of HCF between two singlemode fibers (SMFs).

Vibrational coherence in the composition-selected wavepacket of photoexcited pyrimidine.

Coherent wavepacket motion in photoexcited pyrimidine has been initiated and visualized in real time using femtosecond time-resolved ion-yield spectroscopy. A coherent superposition of at least four low-frequency Frank-Condon (FC) active modes is created in the first excited electronic state (S), leading to a vibrational wavepacket. Its composition is manipulated experimentally by tuning the excitation wavelength in the range 309-313 nm to populate the selected vibrational levels.

Imaging Reversible and Irreversible Structural Evolution in Photoexcited 2,4-Difluoroaniline.

Here, we demonstrate the capability of femtosecond time-resolved photoelectron imaging to visualize the reversible and irreversible structural evolution in electronically excited 2,4-difluoroaniline. As a coherent superposition of out-of-plane vibrational motions is created following 299.8 nm excitation, the molecular geometry alters periodically, thus modulating the photoionization channel.

Unraveling the electronic relaxation dynamics in photoexcited 2,4-difluoroaniline via femtosecond time-resolved photoelectron imaging.

Time-resolved photoelectron imaging is employed to investigate the relaxation dynamics of the lowest two excited electronic states S(ππ*) and S(π3s/πσ*) in 2,4-difluoroaniline (24DFA). As the S(ππ*) state is populated directly following 289 nm excitation, the population undergoes ultrafast intramolecular vibrational redistribution on a 540 fs time scale, followed by efficient intersystem crossing from S(ππ*) to the triplet state within 379 ps, and the subsequent slower deactivation process of the triplet state. For excitation to the S(π3s/πσ*) state at 238 nm, the population probably bifurcates into two decay channels.

Femtosecond time-resolved observation of butterfly vibration in electronically excited o-fluorophenol.

The butterfly vibration during the hydrogen tunneling process in electronically excited o-fluorophenol has been visualized in real time by femtosecond time-resolved ion yield spectroscopy coupled with time-resolved photoelectron imaging technique. A coherent superposition of out-of-plane C-F butterfly motions is prepared in the first excited electronic state (S). As the C-F bond vibrates with respect to the aromatic ring, the nuclear geometry varies periodically, leading to the corresponding variation in the photoionization channel.

Real-time visualization of the vibrational wavepacket dynamics in electronically excited pyrimidine via femtosecond time-resolved photoelectron imaging.

The vibrational wavepacket dynamics at the very early stages of the S-T intersystem crossing in photoexcited pyrimidine is visualized in real time by femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. A coherent superposition of the vibrational states is prepared by the femtosecond pump pulse at 315.3 nm, resulting in a vibrational wavepacket.