deep-UV Pulses Research Articles

Direct temporal characterization of sub-3-fs deep UV pulses generated by resonant dispersive wave emission: erratum

An erratum is presented to include the correct upper horizontal axis in Fig. 3 in our published manuscript [“Direct temporal characterization of sub-3-fs deep UV pulses generated by resonant dispersive wave emission” Opt. Express 31, 26854 (2023).10.1364/OE.494879

Generation of sub-10-fs deep and extreme ultraviolet pulses for time-resolved photoemission spectroscopy.

We present a light source capable of generating sub-10-fs deep UV (DUV) and extreme UV (EUV) pulses for use in time-resolved photoemission spectroscopy. The fundamental output of a Ti:sapphire laser was compressed using the multi-plate method and mixed with the uncompressed second harmonic in a filamentation four-wave mixing process to generate sub-10-fs DUV pulses. Sub-10-fs EUV pulses were generated via high-order harmonic generation driven by the second harmonic pulses that were compressed using Ar gas and chirped mirrors. The minimum cross correlation time between 267 and 57 nm (corresponding to 21.7 eV) was measured to be 10.6 ± 0.4 fs.

Application of deep UV resonance Raman spectroscopy to column liquid chromatography: Development of a low-flow method for the identification of active pharmaceutical ingredients

In this study, deep UV resonance Raman spectroscopy (DUV-RRS) was coupled with high performance liquid chromatography (HPLC) to be applied in the field of pharmaceutical analysis. Naproxen, Metformin and Epirubicin were employed as active pharmaceutical ingredients (APIs) covering different areas of the pharmacological spectrum. Raman signals were successfully generated and attributed to the test substances, even in the presence of the dominant solvent bands of the mobile phase. To increase sensitivity, a low-flow method was developed to extend the exposure time of the sample. This approach enabled the use of a deep UV pulse laser with a low average power of 0.5 mW. Compared to previous studies, where energy-intensive argon ion lasers were commonly used, we were able to achieve similar detection limits with our setup. Using affordable lasers with low operating costs may facilitate the transfer of the results of this study into practical applications.

Generation of high-energy, sub-20 fs deep-UV pulses in a twin-crystal third harmonic generation scheme.

Ultrashort deep ultraviolet (DUV) pulses serve as indispensable tools for investigating molecular dynamics on the femtosecond scale. Nonlinear frequency upconversion of near-infrared (NIR) light sources in a sequence of nonlinear crystals is a common method for their generation. However, preserving the temporal duration of the starting source encounters challenges owing to phase-matching bandwidth limitations within the harmonic generation process. Here we propose an approach for circumventing this limitation and demonstrate it for the case of generation of the third harmonic of 800 nm pulses in a two-stage scheme (second harmonic generation succeeded by sum-frequency mixing of the fundamental and second harmonic pulses). Expanding the bandwidth of the DUV pulse involves the utilization for the last mixing process of two nonlinear crystals, detuned to convert opposite sides of the spectrum. The implementation of this approach yields 20 µJ, 263 nm DUV pulses as short as 19 fs after compression. The setup is very compact and extremely stable due to the common-path scheme, which makes it very interesting for a variety of advanced ultrafast spectroscopy applications.

Direct temporal characterization of sub-3-fs deep UV pulses generated by resonant dispersive wave emission.

We report on the complete temporal characterization of ultrashort pulses, generated by resonant dispersive wave emission in gas-filled hollow-capillary fibers, with energy in the microjoule range and continuously tunable from the deep-ultraviolet to the ultraviolet. Temporal characterization of such ultrabroad pulses, particularly challenging in this spectral region, was performed using an all-in-vacuum setup for self-diffraction frequency resolved optical gating (SD-FROG). Sub-3-fs pulses were measured, tunable from 250 nm to 350 nm, with a minimum pulse duration of 2.4 ± 0.1 fs.

Ablation threshold of GaN films for ultrashort laser pulses and the role of threading dislocations as damage precursors.

The laser-induced ablation threshold of c-plane GaN films upon exposure to ultrashort laser pulses was investigated for different wavelengths from the IR to the UV range and pulse widths between 0.34 and 10 ps. The one-pulse ablation threshold ranges between 0.15 and 3 J/cm2 and shows an increase with the wavelength and the pulse width, except for deep UV pulses. Based on a rate equation model, we attribute this behavior to the efficiency of seed carrier generation by interband absorption. In addition, the multi-pulse ablation threshold was analyzed. Accumulation effects are more prominent in case of IR than with UV pulses and are closely linked to damage precursors. By a thorough structural investigation, we demonstrate that threading dislocations, especially those with a screw component, significantly contribute to laser damage, since they provide a variety of dispersed states within the band gap.

Physical Foundations of Subatomic Attosecond Quantum Technologies for Storing Energy in Materials

The article discusses the current development of physical principles of subatomic quantum technologies using ultrashort attosecond energy pulses within the ranges of deep-UV and soft X-ray radiation. It is necessary as a foundation of the process of nondestructive high-capacity reverse energy harvesting using accumulating nanoelectromechanical systems (NEMS) of supra-atomic scale with linear dimensions of 0.1 nm up to 10 nm and subatomic thickness of boundary interfaces up to 0.1 nm. The article compares the physical principles of up-to-date femtosecond quantum technologies and the prospective attosecond quantum technologies. The latter aims to improve the capacity, controllability, and performance efficiency of quantum energy storages by utilizing quantum electronic excitations of hybrid nature. Harder and shorter by one or two orders of magnitude UV and X-ray impulses are required for attosecond energy storages, unlike the femtosecond ones. Quantum femtochemistry describes the reactions caused by optical spectrum radiation pulses. In the case of attosecond pulses, highly excited quantum entangled subatomic electron pairs demonstrate nonlinear energy pulse accumulation effects. Goldstone condensates of bosonic electron pairs produce boundary shells of compact cavities of a quantum-size NEMS resonator. Hybrid electronic excitations of NEMS are a specific feature of the nonlinear quantum subatomic response of materials to attosecond deep-UV and soft X-ray pulses. The attosecond physics of the processes is the basis for the development of new subatomic attosecond quantum technologies for storing energy in materials.

Exciton decay mechanism in DNA single strands: back-electron transfer and ultrafast base motions.

The photochemistry of DNA systems is characterized by the ultraviolet (UV) absorption of π-stacked nucleobases, resulting in exciton states delocalized over several bases. As their relaxation sensitively depends on local stacking conformations, disentangling the ensuing electronic and structural dynamics has remained an experimental challenge, despite their fundamental role in protecting the genome from potentially harmful UV radiation. Here we use transient absorption and transient absorption anisotropy spectroscopy with broadband femtosecond deep-UV pulses (250–360 nm) to resolve the exciton dynamics of UV-excited adenosine single strands under physiological conditions. Due to the exceptional deep-UV bandwidth and polarization sensitivity of our experimental approach, we simultaneously resolve the population dynamics, charge-transfer (CT) character and conformational changes encoded in the UV transition dipoles of the π-stacked nucleotides. Whilst UV excitation forms fully charge-separated CT excitons in less than 0.3 ps, we find that most decay back to the ground state via a back-electron transfer. Based on the anisotropy measurements, we propose that this mechanism is accompanied by a structural relaxation of the photoexcited base-stack, involving an inter-base rotation of the nucleotides. Our results finally complete the exciton relaxation mechanism for adenosine single strands and offer a direct view into the coupling of electronic and structural dynamics in aggregated photochemical systems.

Full characterization of a phase-locked DUV double pulse generated in an all-reflective shaping setup working under grazing incidence in a broad spectral range

Controlling the temporal and spectral properties of ultrashort laser pulses in the visible and near-infrared spectral range by means of a femtosecond pulse-shaping device is a powerful tool with many applications in ultrafast spectroscopy. A major and successful concept is known as the 4f design, which has a symmetric zero-dispersion-compressor geometry. Most 4f pulse shapers rely on using transmissive optics in their beam path limiting the operational wavelength ranges. In the present contribution, we use an all-reflective shaping setup to generate a phase-locked 266 nm double pulse to benchmark its performance in the limit of short wavelengths. The setup comprises the complete spectral amplitude and phase diagnostics for quantitative analysis of the pulse properties before and after the shaper using the technique of frequency-resolved optical gating. The measured time–frequency spectra are in good agreement with optical simulations. The geometry and hardware of the device including the optical components are designed, such that all harmonics of the deep UV pulses travel the same path, giving the instrument the ability to work with soft X-ray pulses, under vacuum conditions, down to the few-nanometer wavelength scale.

Size evaluation of gold nanoparticles using transient grating method with deep-UV excitation pulses

Transient grating (TG) method was applied for evaluating the size of gold nanoparticles (AuNPs) in aqueous solution. Using nanosecond deep-UV pulses for excitation, AuNPs were reduced to smaller particles, making it feasible to determine their diffusion coefficients and hydrodynamic diameters. The diffusion signals of AuNPs were enhanced significantly by probing at the plasmon resonant wavelength, enabling the data acquisition within a few seconds. The determined hydrodynamic diameters were in agreement with those by other experimental techniques, indicating that the TG method is applicable for size evaluation of these nanoparticles in solution at short time.

Multi-GHz repetition rate, femtosecond deep ultraviolet source in burst mode derived from an electro-optic comb.

We present a femtosecond, 11.48 GHz intra-burst repetition rate deep UV source at 258 nm based on forth-harmonic generation (FHG) of an electro-optic (EO) comb operating in burst mode. Second-harmonic generation (SHG) of the burst-mode EO comb in LiB3O5 (LBO) leads to 3.7 W average power and 242 fs root-mean-square pulse duration. A second stage of SHG is further performed using two separate β-BaB2O4 (BBO) crystals, delivering deep UV pulses at 523 mW and 294 mW, with estimated pulse durations of half-ps and sub-300 fs, respectively. At divided pulse repetition rates of 5.7 GHz and 2.9 GHz, FHG is also demonstrated, highlighting the potential of flexible repetition rate operation at the GHz level.

Ultrafast broadband circular dichroism in the deep ultraviolet

The measurement of chirality and its temporal evolution are crucial for the understanding of a large range of biological functions and chemical reactions. Steady-state circular dichroism (CD) is a standard analytical tool for measuring chirality in chemistry and biology. Nevertheless, its push into the ultrafast time domain and in the deep-ultraviolet has remained a challenge, with only some isolated reports of subnanosecond CD. Here, we present a broadband time-resolved CD spectrometer in the deep ultraviolet (UV) spectral range with femtosecond time resolution. The setup employs a photoelastic modulator to achieve shot-to-shot polarization switching of a 20 kHz pulse train of broadband femtosecond deep-UV pulses (250–370 nm). The resulting sequence of alternating left- and right-circularly polarized probe pulses is employed in a pump-probe scheme with shot-to-shot dispersive detection and thus allows for the acquisition of broadband CD spectra of ground- and excited-state species. Through polarization scrambling of the probe pulses prior to detection, artifact-free static and transient CD spectra of enantiopure [Ru(bpy)3]2+ are successfully recorded with a sensitivity of <2×10−5 OD (≈0.7 mdeg). Due to its broadband deep-UV detection with unprecedented sensitivity, the measurement of ultrafast chirality changes in biological systems with amino-acid residues and peptides and of DNA oligomers is now feasible.

Аттосекундные нанотехнологии: электронные механизмы формирования неравновесных квантовых супра-атомных наноструктур материалов

A theory of one- and two-electron nonequilibrium phenomena on time-spatial levels of quantum supra-atomic nanostructures in materials caused by deep-UV and soft X-ray attosecond pulses is well developed within the fundamental concept of thermal field dynamics. It is shown that time-base sweep of nonequilibrium processes of supra-atomic level formation caused by attosecond pulses starts with the local birth of coherent-entangled static x-gauge modes of two-electron fluctuation electromagnetic fields. The two-electron fluctuation energy accumulates as a quantum electromechanical energy of static x-gauge modes. It results in spontaneous appearance of static electromagnetic loggie 0.1-10 nm in size that include electron pairs and x-gauge modes. Boundaries of the static electromagnetic loggie have kink topological singularities of x-gauge modes in physical space. Finite loggie of coherent-entangled electron pairs enclose Fermi gas of electrons and nuclei and set a topological matrix of quantum electromechanical interfaces in a material. The quantum topology of loggie spatial carriers is a cover of a quantum topology of atoms and single-electron Fermi gas of condensed state.

High-accuracy deep-UV Ramsey-comb spectroscopy in krypton

In this paper, we present a detailed account of the first precision Ramsey-comb spectroscopy in the deep UV. We excite krypton in an atomic beam using pairs of frequency-comb laser pulses that have been amplified to the millijoule level and upconverted through frequency doubling in BBO crystals. The resulting phase-coherent deep-UV pulses at 212.55 nm are used in the Ramsey-comb method to excite the two-photon 4p^6 rightarrow 4p^5 5p [1/2 ]_0 transition. For the {}^{84}hbox {Kr} isotope, we find a transition frequency of 2829833101679(103) kHz. The fractional accuracy of 3.7,times10^{-11} is 34 times better than previous measurements, and also the isotope shifts are measured with improved accuracy. This demonstration shows the potential of Ramsey-comb excitation for precision spectroscopy at short wavelengths.

Ultrafast Photoelectron Imaging Using Tunable UV and Vacuum UV Pulses

Abstract We have constructed an ultrafast laser system that generates both a tunable deep UV pulse and a 158 nm vacuum UV pulse, and performed photoelectron imaging of pyrazine in a supersonic molecular beam. The time-resolution was estimated to be 0.3 ps from a Xe photoionization cross-correlation measurement. The picosecond decay time of the S1(n, π*) state populated by 251 nm excitation was found to be shorter than that previously measured using 264/266 nm excitation. The 3s and 3p Rydberg states excited using the 158 nm pulse were also observed.

Generation of 30 fs pulses tunable from 189 to 240 nm with an all-solid-state setup

Fully tunable deep UV pulses of 30 fs duration are generated in an all-solid-state scheme from 200 fs long pump pulses of a Ti:sapphire amplifier. The tunability comes from a noncollinear optical parametric amplifier with tailored spectral width. The output pulses are frequency-doubled in a 50 μm BBO crystal and subsequently mixed in a 32 μm BBO crystal with part of the Ti:sapphire output. The compression is solely performed in the visible. This makes the setup extremely simple and efficient. Less than 400 μJ pump energy suffice to obtain submicrojoule deep UV pulses. The strategy for the bandwidth and chirp management is explained in detail.

Deep-ultraviolet picosecond flat-top pulses by chirp-matched sum frequency generation

Picosecond, flat-top, deep-UV pulses are needed to generate high-brightness electron beams to efficiently drive x-ray free electron lasers. Current metal photocathodes have low efficiency and therefore require high-energy pulses, and the generation of high-energy, flat-top pulses in the deep UV is still challenging. The low efficiencies of both the harmonic generation and deep-UV pulse shapers restrict the accessible pulse energy. Moreover, the acceptance bandwidth of the harmonic generation limits the minimum rise time of the flat-top profile. We present the generation of few-hundred microjoule, picosecond, deep-UV pulses using chirp-matched sum frequency generation. This scheme combined with IR spectral manipulation is a novel approach for deep-UV pulse shaping. It permits flat-top pulses with high energy and fast rise time, highly suited for high-brightness photoelectron beam production.

Generation and Optimization of Femtosecond Pulses by Four-Wave Mixing Process

Four-wave mixing (FWM) was used to generate and optimize ultrashort pulses with wavelengths from ultraviolet (UV) to near-infrared in bulk media and gases. Wavelength-tunable multicolored pulses were simultaneously generated by cascaded FWM in glass plates. By using incident chirped pulses, 15-fs self-compressed multicolored pulses were obtained with excellent properties. Self-compression was also used to generate ultrashort deep-UV (DUV) pulses. The positive frequency chirp in a self-phase-modulated pulseissuitable for this objective. Sub-10-fs DUV pulses were generated without using any additional pulse compressors. Self-diffraction was used to clean the pulse, broaden the spectrum, and enhance the spatial beam quality. These multicolored pulses can be simultaneously amplified and compressed by a four-wave optical parametric amplifier. The generated multicolored pulses are useful for multicolored ultrafast spectroscopy, microscopy experiments, and as seeds for petawatt lasers with high temporal contrasts.

Sub-10 fs deep-ultraviolet pulses generated by chirped-pulse four-wave mixing

We propose and demonstrate experimentally a novel way of generating sub-10fs deep-UV pulses. The technique is based on chirped-pulse four-wave mixing induced by a broadband near-IR (NIR) pulse and a near-UV pulse. The broadband IR pulse is prepared by preliminarily broadening the spectral width of an NIR pulse by self-phase modulation. The positively chirped broadband IR pulse is suitable for generating a negatively chirped deep-UV pulse, which can be compressed by normal group-velocity dispersion in a transparent medium. Self-compression of the generated deep-UV pulse in air has been demonstrated to produce sub-10fs deep-UV pulses with excellent temporal and spectral profiles for ultrafast spectroscopy in the deep UV.

Generation of high-energy sub-20 fs pulses tunable in the 250-310 nm region by frequency doubling of a high-power noncollinear optical parametric amplifier

We report on the generation of powerful sub-20 fs deep UV pulses with 10 microJ level energy and broadly tunable in the 250-310 nm range. These pulses are produced by frequency doubling a high-power noncollinear optical parametric amplifier and compressed by a pair of MgF2 prisms to an almost transform-limited duration. Our results provide a power scaling by an order of magnitude with respect to previous works.