Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCovariance spectroscopy of molecular gases using fs pulse bursts created by modulational instability in gas-filled hollow-core fiber
86
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present a technique that uses noisy broadband pulse bursts generated by modulational instability to probe nonlinear processes, including infrared-inactive Raman transitions, in molecular gases. These processes imprint correlations between different regions of the noisy spectrum, which can be detected by acquiring single shot spectra and calculating the Pearson correlation coefficient between the different frequency components. Numerical simulations verify the experimental measurements and are used to further understand the system and discuss methods to improve the signal strength and the spectral resolution of the technique.
rate research
Read More
Gas-filled hollow-core photonic crystal fiber (PCF) is used for efficient nonlinear temporal compression of femtosecond laser pulses, two main schemes being direct soliton-effect self-compression, and spectral broadening followed by phase compensation. To obtain stable compressed pulses, it is crucial to avoid decoherence through modulational instability (MI) during spectral broadening. Here we show that changes in dispersion due to spectral anti-crossings between the fundamental core mode and core wall resonances in anti-resonant-guiding hollow-core PCF can strongly alter the MI gain spectrum, enabling MI-free pulse compression for optimized fiber designs. In addition, higher-order dispersion can introduce MI even when the pump pulses lie in the normal dispersion region.
In this letter, an energetic and highly efficient dispersive wave (DW) generation at 200 nm has been numerically demonstrated by selectively exciting LP$_{02}$-like mode in a 10 bar Ar-filled hollow-core anti-resonant fiber pumping in the anomalous dispersion regime at 1030 nm with pulses of 30 fs duration and 7 $mu$J energy. Our calculations indicate high conversion efficiency of $>$35% (2.5 $mu$J) after propagating 3.6 cm fiber length which is due to the strong shock effect and plasma induced blue-shifted soliton. It is observed that the efficiency of fundamental LP$_{01}$-mode is about 15% which is much smaller than LP$_{02}$-like mode and also emitted at longer wavelength of 270 nm.
We report on a highly-efficient experimental scheme for the generation of deep-ultraviolet ultrashort light pulses using four-wave mixing in gas-filled kagome-style photonic crystal fiber. By pumping with ultrashort, few $mu$J, pulses centered at 400 nm, we generate an idler pulse at 266 nm, and amplify a seeded signal at 800 nm. We achieve remarkably high pump-to-idler energy conversion efficiencies of up to 38%. Although the pump and seed pulse durations are ~100 fs, the generated ultraviolet spectral bandwidths support sub-15 fs pulses. These can be further extended to support few-cycle pulses. Four-wave mixing in gas-filled hollow-core fibres can be scaled to high average powers and different spectral regions such as the vacuum ultraviolet (100-200 nm).
A recently developed source of ultraviolet radiation, based on optical soliton propagation in a gas-filled hollow-core photonic crystal fiber, is applied here to angle-resolved photoemission spectroscopy (ARPES). Near-infrared femtosecond pulses of only few {mu}J energy generate vacuum ultraviolet (VUV) radiation between 5.5 and 9 eV inside the gas-filled fiber. These pulses are used to measure the band structure of the topological insulator Bi2Se3 with a signal to noise ratio comparable to that obtained with high order harmonics from a gas jet. The two-order-of-magnitude gain in efficiency promises time-resolved ARPES measurements at repetition rates of hundreds of kHz or even MHz, with photon energies that cover the first Brillouin zone of most materials.
The possibility of performing time-resolved spectroscopic studies in the molecular fingerprinting region or extending the cut-off wavelength of high-harmonic generation has recently boosted the development of efficient mid-infrared ultrafast lasers. In particular, fibre lasers based on active media such as thulium or holmium are a very active area of research since they are robust, compact and can operate at high repetition rates. These systems, however, are still complex, are unable to deliver pulses shorter than 100 fs and are not yet as mature as their near-infrared counterparts. Here we report generation of sub-40 fs pulses at 1.8 microns, with quantum efficiencies of 50% and without need for post-compression, in hydrogen-filled hollow-core photonic crystal fibre pumped by a commercial 300-fs fibre laser at 1030 nm. This is achieved by pressure-tuning the dispersion and avoiding Raman gain suppression by adjusting the chirp of the pump pulses and the proportion of higher order modes launched into the fibre. The system is optimized using a physical model that incorporates the main linear and nonlinear contributions to the optical response. The approach is average power-scalable, permits adjustment of the pulse shape and can potentially allow access to much longer wavelengths.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
