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Intrinsic photophysics of nitrophenolate ions studied by cryogenic ion spectroscopy
摘要： The intrinsic photophysics of nitrophenolate isomers (meta, para, and ortho) was studied at low temperature using photodissociation mass spectrometry in a cryogenic ion trap instrument. Each isomer has distinct photophysics that affects the excited state lifetimes, as observed experimentally in their spectroscopic linewidths. Visible-light-induced excitation of m-nitrophenolate gives rise to well-resolved vibronic features in the spectrum of the S1 state. The para and ortho isomers have broad spectra – even at cryogenic temperatures – due to their shorter excited state lifetimes and spectral congestion. We present computational evidence for mixing of the first and second excited states of o-nitrophenolate, leading to significant additional broadening in the experimental spectrum.
关键词： excited state lifetimes,cryogenic ion spectroscopy,photophysics,spectral broadening,nitrophenolate
更新于2025-09-19 17:15:36
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Spectral broadening of a KrF laser via propagation through Xe in the negative nonlinear index regime
摘要： In inertial con?nement (ICF) experiments at the NIKE laser facility, the high-power krypton ?uoride (KrF) laser output beams propagate through long (～75 m) air paths to achieve angular multiplexing, which is required because the KrF medium does not store energy for a suf?ciently long time. Recent experiments and simulations have shown that, via stimulated rotational Raman scattering, this propagation can spectrally broaden the laser beam well beyond the ～1 THz laser linewidth normally achieved by the induced spatial incoherence (ISI) technique used in NIKE. These enhanced bandwidths may be enough to suppress the laser-plasma instabilities which limit the maximum intensity that can be incident on the ICF target. In this paper we investigate an alternative technique that achieves spectral broadening by self-phase modulation in Xe gas, which has a large, negative nonlinear refractive index ～248 nm, and thus completely avoids transverse ?lamentation issues. The collective, nonlinear atomic response to the chaotic, nonsteady state ISI light is modeled using a two-photon vector model, and the effect of near-resonant behavior on the spectral broadening is studied.
关键词： self-phase modulation,laser-plasma instabilities,negative nonlinear index,KrF laser,spectral broadening,Xe gas
更新于2025-09-16 10:30:52
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Nonlinear Fiber Optics || Self-phase modulation
摘要： The ?rst nonlinear effect that we focus on is the self-phase modulation (SPM), a phenomenon that leads to spectral broadening of optical pulses [1–9]. SPM is the temporal analog of self-focusing of CW beams occurring inside any nonlinear medium with n2 > 0. It was ?rst observed in 1967 in the context of transient self-focusing of optical pulses propagating through a CS2-?lled cell [1]. By 1970, SPM had been observed in solids and glasses by using picosecond pulses. The earliest observation of SPM in optical ?bers was made with a ?ber whose core was ?lled with CS2 liquid [7]. This work led by 1978 to a systematic study of SPM in a silica-core ?ber [9]. This chapter considers SPM as a simple example of the nonlinear effects that can occur inside optical ?bers. Section 4.1 is devoted to the case of pure SPM as it neglects the GVD effects and focuses on spectral changes induced by SPM. The combined effects of GVD and SPM are discussed in Section 4.2 with emphasis on the SPM-induced frequency chirp. Section 4.3 presents two analytic techniques and uses them to solve the NLS equation approximately. Section 4.4 extends the analysis to include the higher-order nonlinear effects such as self-steepening.
关键词： GVD,self-steepening,spectral broadening,optical pulses,frequency chirp,SPM,nonlinear effects,NLS equation,self-phase modulation
更新于2025-09-12 10:27:22
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Dramatic Spectral Broadening of Ultrafast Laser Pulses in Molecular Nitrogen Ions <sup>*</sup>
摘要： We investigate nonlinear interaction of nitrogen molecules with a two-color laser field composed by an intense 800 nm laser pulse and a weak 400 nm laser pulse. It is demonstrated that the spectrum of 400 nm pulses is dramatically broadened when the two beams temporally overlap. In comparison, the spectral broadening in argon is less pronounced, although argon atoms and nitrogen molecules have comparable ionization potentials. We reveal that the dramatic spectral broadening originates from the greatly enhanced nonlinear optical effects in the near-resonant condition of interaction between the 400 nm pulses and the nitrogen molecular ions.
关键词： two-color laser field,spectral broadening,nonlinear interaction,nitrogen molecular ions
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Soliton Self-Compression and Spectral Broadening of 1 μm Femtosecond Pulses in Single-Domain KTiOPO <sub/>4</sub>
摘要： Efficient, diode-pumped high energy femtosecond laser systems around 1 μm based on Yb-gain media are readily commercially available. However, owing to the gain bandwidth limitations, the pulses generated in such lasers are substantially longer than the ones generated in Ti:Sapphire systems. A simple, energy-scalable pulse self-compression scheme for the pulses around 1 μm thus would be of great interest for many applications, including time-resolved pump-probe spectroscopy, high-harmonics generation, etc. The self-phase modulation during nonlinear propagation in filaments in gasses is often employed for pulse self-compression [1,2]. Such schemes typically require rather bulky setups and careful control of group velocity dispersion. Some years ago it has been shown theoretically that Raman-active molecules in gaseous form could be used for mid-infrared pulse compression [3]. Here we exploit highly-efficient interaction of optical pulses with phonon-polaritons in KTiOPO4 (KTP) [4] for self-compression of fs pulses at 1 μm. The experimental setup consists of a 1030 nm femtosecond pump laser. The pulses were loosely focused by a f=150 mm lens to a beam waist with 1/e2 radius of 160 μm in a 10 mm-long, 5mm-thick single-domain KTP sample. The pulses were polarized along the c-axis of the crystal. The dependence of the pulse output spectrum as a function of the beam focus position in the crystal is shown in Fig.1 (a), where 300 fs full width at half maximum (FWHM) input pulses from a fiber-based system were employed. The broadest spectrum was obtained with the focal plane being located close to the entrance of the crystal. We employed time-resolved digital holography [5] to verify the coupling of the optical pulse with phonon-polariton wave during propagation through the crystal. Characterization experiments with 173 fs FWHM pulses derived from a commercial solid-state laser system were conducted using a custom-built d-scan setup [6]. The setup included chirped mirrors covering the spectral region of Fig.1 (a).
关键词： Femtosecond Pulses,KTiOPO4,Spectral Broadening,Soliton Self-Compression,Phonon-polaritons
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Multipass Spectral Broadening with Tens of Millijoule Pulse Energy
摘要： Nonlinear spectral broadening is widely used for applications like attosecond pulse generation, XUV sources, supercontinuum generation or ultrafast spectroscopy. In these cases the laser is typically spectrally broadened and compressed to reach pulse durations much shorter than originally available. For pulse energies in the millijoule regime, spectral broadening is routinely implemented using capillary optical fibers with remarkable results in terms of output pulse durations and beam quality. In addition to fiber-based approaches, the application of multipass cells for spectral broadening recently attracted increasing interest. These cells are capable of preserving a nearly Gaussian mode in the presence of nonlinear effects without a spatial filter or optical fiber, they are robust to input pointing, have a high throughput of more than 90% and can be used with high average powers and energies. In a multipass cell the nonlinear interaction with either gas or a thin solid provides a small amount of spectral broadening within each pass. Based on this concept we recently demonstrated output energies of almost 18 mJ by guiding near infrared pulses with a pulse duration of 1.3 ps and a repetition rate of 5 kHz through an argon filled multipass cell. We obtained a broadening factor of over 33 and could show compressibility down to 41 fs. The energy was limited by the breakdown intensity of argon and the damage threshold of the used optics. To increase the throughput energy, we developed a new mirror coating with a damage threshold measured to be about 50% higher than the coating used in [4]. The setup length was increased from 3m to 8m leading to about 170% bigger beam areas. Output energies of 39.5 mJ with a broadening factor over 38 (output bandwidth 85nm at 20 dB, output fourier limit 34.2 fs) are reached in first experiments by focusing a 1.3 ps pulse 43 times in 250 mBar of argon (cf. Fig. 1 and Fig. 2). The beam profile after propagation depicted as inset in Fig. 2 keeps its nearly Gaussian shape indicating a preserved beam quality. The throughput is well above 95% with an output spectrum typical for self-phase modulation. Ongoing optimization is expected to lead to even higher throughput energies. This laser source will combine pulse durations below 40 fs with high energies and kilohertz repetition rate and can be used as driver laser for an all-laser-driven Thomson X-ray source yielding a significant increase of photon flux. Moreover this technique is widely applicable to different wavelength ranges, input energies and input powers turning it into a promising scalable alternative to fiber based spectral broadening.
关键词： multipass cells,Nonlinear spectral broadening,pulse compression,high-energy lasers
更新于2025-09-11 14:15:04
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Comparison of HPHT and LPHT annealing of Ib synthetic diamond
摘要： Defect transformations in type Ib synthetic diamond annealed at a temperature of 1870 °C under stabilizing pressure (HPHT annealing) and in hydrogen atmosphere at normal pressure (LPHT annealing) are compared. Spectroscopic data obtained on the samples before and after annealing prove that the processes of nitrogen aggregation and formation of nitrogen-nickel complexes are similar in both cases. Essential differences between HPHT and LPHT annealing are stronger graphitization at macroscopic imperfections and enhanced lattice distortions around point defects in the latter case. The lattice distortion around point defects is revealed as a considerable broadening of zero-phonon lines of "soft" (vacancy-related) optical centers. It was found that LPHT annealing may enhance overall intensity of luminescence of HPHT-grown synthetic diamonds.
关键词： nitrogen aggregation,graphitization,low pressure high temperature annealing,synthetic type Ib diamond,spectral broadening,high pressure high temperature annealing
更新于2025-09-10 09:29:36
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Role of Multiphoton Ionization in the Short-Wavelength Broadening of the Spectrum of a Light Bullet in the Middle Infrared Range
摘要： The short-wavelength cutoff of the anti-Stokes wing of the supercontinuum in the spectrum of a light bullet at filamentation of femtosecond radiation at a wavelength tunable in a wide range of the middle infrared range in fused silica and fluorides has been studied for the first time. A physical model for the formation of the spectrum of the light bullet has been proposed on the basis of the spectral broadening caused by the phase self-modulation of the light field on the trailing edge of the light bullet at the generation of a plasma in the process of multiphoton ionization. Within this model, a function has been obtained to determine the wavelength shift of the short-wavelength cutoff as a function of the multiphoton order. This function is in agreement with experimental results.
关键词： supercontinuum,light bullet,spectral broadening,multiphoton ionization,middle infrared range
更新于2025-09-04 15:30:14