High-energy ultraviolet dispersive-wave emission in compact hollow capillary systems

Abstract

We demonstrate high-energy resonant dispersivewave emission in the deep ultraviolet (218 to 375 nm) from optical solitons in short (15 to 34 cm) hollow capillary fibres. This down-scaling in length compared to previous results in capillaries is achieved by using small core diameters (100 and 150 µm) and pumping with 6.3 fs pulses at 800 nm. We generate pulses with energies of 4 to 6 µJ across the deep ultraviolet in a 100 µm capillary and up to 11 µJ in a 150 µm capillary. From comparisons to simulations we estimate the ultraviolet pulse to be 2 to 2.5 fs in duration. We also numerically study the influence of pump duration on the bandwidth of the dispersive wave. Optical soliton dynamics, obtained by balancing linear and nonlinear contributions to the phase of a propagating light pulse, are a key phenomenon in nonlinear fibre optics. Resonant dispersive wave (RDW) emission in gas-filled hollow fibres is a particularly promising application of this effect, enabling the generation of tuneable ultrashort pulses and supercontinua at shorter wavelengths than possible in any solid-core waveguide [1,2,3,4,5], from the vacuum ultraviolet to the visible spectral region. These dynamics were pioneered in hollow-core photonic-crystal fibres (HC-PCF). Recently, we demonstrated that they can be scaled in energy by up to several orders of magnitude in simple hollow capillary fibres (HCF) [5]. Pumping gas-filled large-core HCF with 10 fs pulses enabled soliton self-compression to 1 fs in the near infrared-an optical attosecond pulse-and the generation of few-femtosecond vacuum and deep ultraviolet (VUV/DUV) pulses at unprecedented peak power, comparable to free-electron lasers. We also showed that up-scaling of those dynamics to the terrawatt scale is feasible by further increasing the HCF core size. Here, we down-scale the core size instead to achieve a more compact and practical setup. Whereas our first demonstration made use of 3 m HCF, here we show that this can be reduced to just 15 to 34 cm when using small-core HCF and even shorter pump pulses-6.3 fs, as readily generated in widely used conventional HCF pulse compression systems. The required pulse energy is also reduced, which is an additional advantage if multiple frequency conversion schemes are to be driven simultaneously, as for instance in multi-colour time-resolved spectroscopy experiments.The HCF length required to generate a dispersive wave is primarily determined by the distance over which soliton selfcompression occurs. This is well approximated by the fission length L f ,where N is the soliton order and L d and L nl are the dispersion and nonlinear lengths, describing the length scales of groupvelocity dispersion (GVD) and self-phase modulation (SPM), respectively [6]. Broadly similar soliton dynamics and RDW emission can be obtained with different parameters, provided that the soliton order and the zero-dispersion wavelength λ zd remain the same. In particular, the spectral location of RDW emission is chiefly determined by the pump wavelength λ0 and λ zd . W...

Infrared attosecond field transients and UV to IR few-femtosecond pulses generated by high-energy soliton self-compression

“…It is not necessary in the present experiment-significantly simplifying the setup-due to the wavelength dependence of the waveguide dispersion. The length scale of soliton self-compression is largely determined by the pulse duration and the dispersion at the driving wavelength, with shorter pulses and larger (more anomalous) dispersion leading to more rapid self-compression [15,16]. While the HCF has to be larger for longer driving wavelengths to compensate for increased loss (the propagation loss α scales with the wavelength λ and the core radius a as α ∝ λ 2 /a 3 ) nevertheless the anomalous dispersion contribution of the waveguide is stronger (it scales as λ 3 /a 2 ).…”

“…With shorter driving pulses, soliton self-compression occurs over shorter distances, allowing the use of smaller core sizes and lower overall energy as well as making the system more compact [16]. We apply this principle to demonstrate that tunable RDW emission from the ultraviolet to near infrared can also be obtained with driving pulse energies of less than 200 μJ in a compact system.…”

“…For low (few-microjoule) pulse energies, antiresonant photonic crystal fibers (AR-PCFs) offer low-loss guidance with small core diameters (typically around 30 μm), and soliton effects have been demonstrated at a variety of driving wavelengths [10][11][12][13][14]. Recently, we have shown that soliton dynamics can be observed in HCFs at much higher energies by employing precompressed driving pulses [15,16]. In numerical studies, moderate self-compression at 1800 nm [17] as well as subcycle pulse generation in the midinfrared [18] have previously been predicted, however no experiments have been performed to date.…”

Low-noise tunable deep-ultraviolet supercontinuum laser

“…A promising approach to develop a tunable UV laser is to utilize and combine the emerging hollow core (HC) fiber technology with noble nonlinear gases. This has been achieved at multi-gigawatt peak powers using capillary fibers 8 , 9 . HC photonic-crystal fibers (PCFs) 10 offer a viable option for lower peak power levels, and with improved loss properties they offer a more practical implementation than capillaries.…”

Carrier-envelope-phase-stable soliton-based pulse compression to 44 fs and ultraviolet generation at the 800 kHz repetition rate

“…DW emission has been widely exploited in both solid and hollow-core fibers for efficient and tunable frequency up-and down-conversion [25]. In HC fibers tunability from the visible down to the vacuum UV has been demonstrated at pump laser repetition rates from 1 kHz to 10 MHz [10,[26][27][28], with conversion efficiencies up to 15% [26].…”