Generation Of High-energy Pulses Research Articles

Plasma-based generation and control of a single few-cycle high-energy ultrahigh-intensity laser pulse.

A laser-boosted relativistic solid-density paraboloidal foil is known to efficiently reflect and focus a counterpropagating laser pulse. Here we show that in the case of an ultrarelativistic counterpropagating pulse, a high-energy and ultrahigh-intensity reflected pulse can be more effectively generated by a relatively slow and heavy foil than by a fast and light one. This counterintuitive result is explained with the larger reflectivity of a heavy foil, which compensates for its lower relativistic Doppler factor. Moreover, since the counterpropagating pulse is ultrarelativistic, the foil is abruptly dispersed and only the first few cycles of the counterpropagating pulse are reflected. Our multidimensional particle-in-cell simulations show that even few-cycle counterpropagating laser pulses can be further shortened (both temporally and in the number of laser cycles) with pulse amplification. A single few-cycle, multipetawatt laser pulse with several joules of energy and with a peak intensity exceeding 10(23) W/cm(2) can be generated already employing next-generation high-power laser systems. In addition, the carrier-envelope phase of the generated few-cycle pulse can be tuned provided that the carrier-envelope phase of the initial counterpropagating pulse is controlled.

Divided-pulse compression with gas-filled hollow-core fiber for generation of high-energy few-cycle pulses

We study theoretically a pulse compression method with gas-filled hollow-core fiber (HCF) based on pulse division. The input pulse is first divided temporally into a sequence of almost identical subpulses by birefringent optical elements that are designed to have nearly zero group delay dispersion. Then, these subpulses are coupled into gas-filled HCF for spectrum broadening independently. Last, the subpulses are recombined into one pulse by the birefringent elements and compressed temporally. This method is demonstrated to be suitable for compressing ultrafast pulses with energies far above the millijoule to few-cycle level. Several key issues on successfully implementing this method are analyzed quantitatively, and the limitations are also discussed.

Generation of high-energy dual-wavelength domain wall pulse with low repetition rate in an HNLF-based fiber ring laser

The generation of high-energy dual-wavelength domain wall pulse with a low repetition rate is demonstrated in a highly nonlinear fiber (HNLF)-based fiber ring laser. By introducing the intracavity birefringence-induced spectral filtering effect, the dual-wavelength lasing operation can be achieved. In order to enhance the cross coupling effect between the two lasing beams for domain wall pulse formation, a 215-m HNLF is incorporated into the laser cavity. Experimentally, it is found that the dual-wavelength domain wall pulse with a repetition rate of 77.67 kHz could be efficiently obtained through simply rotating the polarization controller (PC). At a maximum pump power of 322 mW, the 655-nJ single pulse energy in cavity is obtained. The proposed configuration provides a simpler and more efficient way to generate high energy pulse with a low repetition rate.

Carrier-envelope phase stability of hollow fibers used for high-energy few-cycle pulse generation

We investigated the carrier-envelope phase (CEP) stability of hollow-fiber compression for high-energy few-cycle pulse generation. Saturation of the output pulse energy is observed at 0.6mJ for a 260μm inner-diameter, 1m long fiber, statically filled with neon. The pressure is adjusted to achieve output spectra supporting sub-4-fs pulses. The maximum output pulse energy can be increased to 0.8mJ by either differential pumping (DP) or circularly polarized input pulses. We observe the onset of an ionization-induced CEP instability, which saturates beyond input pulse energies of 1.25mJ. There is no significant difference in the CEP stability with DP compared to static-fill.

Generation of high-energy broadband femtosecond deep-ultraviolet pulses by highly nondegenerate noncollinear four-wave mixing in a thin transparent solid

We present a simple and efficient technique for the generation of ultrashort deep-ultraviolet pulses based on four-wave mixing of noncollinear laser pulses in a thin solid. Sub-30-fs pulses (Fourier-limit of 13 fs) centered at 270 nm, with energies up to 6 μJ, were obtained by mixing the fundamental and the second harmonic of a Ti:sapphire amplifier in fused silica. Temporal characterization was performed with a dispersionless self-diffraction FROG setup. Spectra as broad as 20 nm were also obtained that can in principle support sub-4-fs deep-ultraviolet pulses.The results are well described by two-dimensional numerical simulations.

A controllable noise-like operation regime in a Yb-doped dispersion-mapped fiber ring laser

We report the generation of tunable high-energy noise-like pulses with a super-broadband spectrum from a Yb-doped dispersion-mapped fiber ring laser. Self-starting noise-like operation can be maintained over a relatively large range of pumping powers (4–13 W). The corresponding output power varies from 0.1 to 1.45 W. The maximum 3 dB spectral bandwidth of the noise-like pulses is about 48.2 nm while the output energy is as high as 47 nJ, limited by optical damage of the components. The central wavelength of the noise-like pulses can be tuned easily over ∼12 nm. The bandwidth and duration of the generated wave packets can also be controlled. The use of a negative dispersion-delay line and spectral filter are found to be important for generating such high-power noise-like operation. Experimental results are in good agreement with theoretical simulations.

Sub-5-ps, multimegawatt peak-power pulses from a fiber-amplified and optically compressed passively Q-switched microchip laser

We report on high-energy picosecond pulse generation from a passively Q-switched and fiber-amplified microchip laser system. Initially, the utilized microchip lasers produce pulses with durations of around 100 ps at 1064 nm central wavelength. These pulses are amplified to energies exceeding 100 μJ, simultaneously chirped and spectrally broadened by self-phase modulation using a double stage amplifier based on single-mode LMA photonic crystal fibers at repetition rates of up to 1 MHz. Subsequently, the pulse duration of chirped pulses is reduced by means of nonlinear pulse compression to durations of 2.7 ps employing a conventional grating compressor and 4.7 ps using a compact compressor based on a chirped volume Bragg grating.

Cavity-length optimization for high energy pulse generation in a long cavity passively mode-locked all-fiber ring laser

In order to achieve higher pulse energy in a passively mode-locked fiber ring laser, a long cavity length is commonly implemented. However, a long cavity operating in the anomalous dispersion regime also leads to pulse broadening, which reduces the average pulse power. In this paper, the trade-off between cavity length and average pulse power is investigated with the aim of optimizing the cavity length to achieve maximum pulse energy. Numerical simulation results, presented here, indicate that there exists an optimum cavity length for which the pulse energy is maximum and the optimum length shifts as the pump power changes. The simulation results for a pump power of 500 mW are verified by measurements carried out on a long cavity nonlinear polarization rotation mode-locked all-fiber ring laser operating in the anomalous dispersion regime. With a repetition rate of 266 kHz for the dissipative solitons, we achieve a pulse energy of 139.1 nJ for a cavity length of 700 m. Higher pulse energy can be expected by using a pump laser diode with higher pump power.

Carbon-nanotube-based passively Q-switched fiber laser for high energy pulse generation

We demonstrate a passively Q-switched erbium-doped fiber laser using a carbon-nanotube-based saturable absorber via evanescent field interaction. The carbon nanotubes are deposited on a side-polished fiber by optically-driven deposition method. Since only the evanescent field of the propagating light interacts with carbon nanotubes in saturable absorber, the fiber laser can maintain a relatively high intra-cavity power and output pulses with energy of 81.3nJ are obtained with a repetition rate of 70.4kHz and a pulse width of 4.5μs.

Generation of 25-fs High Energy Pulses by SPM-Induced Spectral Broadening in a Photonic Crystal Fiber Laser System

We demonstrate 25-fs laser pulse generation from a photonic crystal fiber (PCF) laser system, which consists of a high energy all normal dispersion mode-locked oscillator based on an ytterbium-doped large mode area PCF and a passive PCF-based grating-pair compressor. The oscillator directly delivers 314-nJ highly-chirped pulses with a duration of 1.32 ps at a repetition rate of 15.58 MHz, which can be dechirped to 75 fs, corresponding to a peak power of 3 MW. The output laser pulses from the oscillator are directly injected to a piece of passive PCF for spectral broadening and dechirped by a transmission grating pair compressor, which results in a short pulse duration of 25 fs with 1-W average power.

Generation of High-Energy Few-Cycle Laser Pulses by Using the Ionization-Induced Self-Compression Effect

A mechanism behind the ionization-induced self-compression effect for ultrashort laser pulses propagating in gas-filled capillaries is proposed. It is shown that as a result of excitation of the nonlinear-plasma waveguide laser pulses producing gas ionization can be self-compressed to few-cycle duration. This effect is used for high-energy laser pulses and its scalability to J-level energies is demonstrated.

Spatial shaping of intense femtosecond beams for the generation of high-energy attosecond pulses

We generate high-order harmonics with a spatially shaped TW laser beam. We present and analyse in detail a new approach for shaping an intense laser field to a flat-top intensity profile near focus. We show that this approach is well adapted for high harmonic generation with high-energy fundamental pulses and highlight the possibilities for generating high-energy attosecond pulses.

Wavelength tunable, high energy femtosecond laser pulses directly generated from large-mode-area photonic crystal fiber

Wavelength tunable high energy ultrashort laser pulses are generated from a large-mode-area photonic crystal fiber in anomalous dispersion (AD) regime. A simplified laser cavity design with one fine polished facet of the fiber as a cavity mirror is used. The intra-cavity dispersion compensation is achieved by a grating pair, the spatial dispersed light from which also have optical spectrum filtering effects combined with the limited aperture of the fiber core. The laser system is able to generate ultrashort pulses ranging from 494fs (with 56nJ pulse energy) to 1.24ps (with 49nJ pulse energy) at 55MHz repetition rate. The filtering mechanism benefits the generation of high energy pulses with narrowing pulse duration in AD regime. An undulation in frequency and time domain is also observed with the increase of the pump power. Furthermore, this laser system is directly used as seed for supercontinuum generation.

Vertical cavity surface emitting lasers with the active layer position detuned from standing wave antinode for picosecond pulse generation by gain switching

A vertical cavity surface emitting laser with the active layer position detuned from the standing wave antinode is proposed for the purpose of high energy picosecond pulse generation by gain switching and analysed using numerical simulations and a fully analytical model. An optimum value of the confinement factor for high-energy pulse generation is predicted and its origins discussed.

On the mode-locking mechanism of a dissipative- soliton fiber oscillator

We report on the generation of high-energy pulses in an all normal dispersion photonic-crystal fiber laser. Two mode-locking techniques with and without passive spectral filtering are studied both numerically and experimentally to address a roadmap for energy scaling. It is found that high-contrast passive modulation is a very promising mode-locking technique for energy scaling in dissipative-soliton laser. Moreover, this technique does not need any additional spectral filtering than the limited gain bandwidth to stabilize high-energy ultrashort pulses. The presented laser generates 110 nJ chirped pulses at 57 MHz repetition rate for an average power of 6.2 W. The output pulses could be dechirped close to the transform-limited duration of 100 fs.

Mode-locked 05 μJ fiber laser at 976 nm

We report on high-energy femtosecond pulse generation from an ytterbium-doped rod-type fiber oscillator emitting around 976 nm. Self-starting and stable single-pulse operation are demonstrated with 4.2 W of average output power at a repetition rate of 8.4 MHz. The resulting energy level reaches 0.5 μJ. Because of the all-normal dispersion of the laser cavity, output pulses are naturally chirped with a duration of 14 ps. External compression using diffraction gratings shortens the pulse duration down to 460 fs.

High-energy attosecond light sources

The development of attosecond technology is one of the most significant achievements in the field of ultrafast optics over the past decade. Since the first experimental demonstration of attosecond pulses just ten years ago, novel techniques have been introduced for the generation, characterization and application of subfemtosecond pulses. The development of attosecond tools is continuously triggering the introduction of new spectroscopic and measurement methods, which will offer the opportunity to investigate unexplored research areas with unprecedented time resolution. The wealth of ultrafast processes, which can be investigated by taking advantage of attosecond temporal resolution, can be greatly extended by the development of high-intensity attosecond sources. This Review covers a selection of recent advances in the field of attosecond technology, with particular attention being given to the generation and application of high-energy attosecond pulses.

Tunable high-energy soliton pulse generation from a large-mode-area fiber and its application to third harmonic generation microscopy

We demonstrate high-energy soliton generation from 1580 nm to 2130 nm by using soliton self-frequency shift in a large-mode-area fiber, pumped by a femtosecond fiber laser source. Transformed-limited soliton pulses with 70 fs pulse width and up to 45 nJ pulse energy are obtained. The broad wavelength tuning range and the high soliton pulse energy, together with the robust fiber-based excitation source, offer unprecedented performance, flexibility, and practicality. To demonstrate the application of the soliton pulses, we image the myelin in mouse brain using third harmonic generation microscopy.

Generation of high-energy vacuum UV femtosecond pulses by multiple-beam cascaded four-wave mixing in a transparent solid

The generation of ultrashort vacuum UV (VUV) pulses by nondegenerate cascaded four-wave mixing of femtosecond pulses in a thin slide of a large band-gap transparent solid is numerically demonstrated. Using a novel noncollinear multiple-beam configuration, cascaded four-wave mixing of amplified 30 fs Ti:sapphire laser pulses at 800 nm, and their second harmonic in lithium fluoride results in the generation of VUV radiation down to 134 nm with energies in the μJ range and durations comparable to those of the pump pulses. The proposed geometry is advantageous in large dispersion scenarios, namely for generating radiation close to absorption bands. Hence these results set this technique as a promising way to efficiently generate ultrashort VUV radiation in solids for several applications in science and technology.

Remote generation of high-energy terahertz pulses from two-color femtosecond laser filamentation in air

We experimentally investigated the dynamic behavior of remote terahertz (THz) generation from two-color femtosecond laser-induced filamentation in air. A record-high THz pulse energy of 570 nJ at frequency below 5.5 THz was measured by optimizing the pump parameters at a controllable remote distance of 16 m, while super-broadband THz (300 THz) pulse energy was up to 2.8 \ensuremath{\mu}J. A further energy-scaling possibility was proposed. By analyzing simultaneously the fluorescence from both neutral ${\mathrm{N}}_{2}$ and ${\mathrm{N}}_{2}$${}^{+}$ in the filament, we found that the enhancement of THz radiation was due principally to guiding of the weak second-harmonic pulse inside the filament of the first strong fundamental pulse.