CEP-stable few-cycle light pulses find numerous applications in attosecond science, most notably the production of isolated attosecond pulses for studying ultrafast electronic processes in matter . Scaling up the pulse energy of few-cycle pulses could extend the scope of applications to even higher intensity processes, such as attosecond dynamics of relativistic plasma mirrors .
Hollow fiber compressors are widely used to produce few-cycle pulses with excellent spatiotemporal quality , where octave-spanning broadened spectra can be temporally compressed to sub-2-cycle duration [4,5]. Several tricks help increase the output energy: using circularly polarized light , applying a pressure gradient along the fiber  or even temporal multiplexing . The highest pulse energy of 5 mJ at 5 fs pulse duration was achieved by using a hollow fiber in pressure gradient mode  but in this case no CEP stabilization was achieved, which is crucial for most applications of few-cycle pulses. Nevertheless, it did show that in order to scale up the peak power, the effective length and area mode of the fiber had to be increased proportionally, thereby requiring the use of longer waveguides with larger apertures. Thanks to an innovative design utilizing stretched flexible capillaries , we recently demonstrated the generation CEP-stable sub-4fs pulses with 3mJ energy using a 2m length 450mm bore hollow fiber in pressure gradient mode .
Here, we show that a stretched hollow-fiber compressor operated in pressure gradient mode can generate relativistic intensity pulses with continuously tunable waveform down to almost a single cycle (3.5fs at 750nm central wavelength). The pulses are characterized online using an integrated d-scan device directly under vacuum . While the pulse shape is tuned, all other pulse characteristics, such as energy, pointing stability and focal distribution remain the same on target, making it possible to explore the dynamics of plasma mirrors using controllable relativistic-intensity light waveforms at 1kHz.
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The generation of configurable multipulses by advanced MOPA fiber lasers is opening new possibilities in materials processing, showing improvements in efficiency and quality while benefiting from the advantages of competitively priced fiber lasers. We show examples of the configuration capability and control of multipulses of a 20W MOPA pulsed fiber laser at 1.06μm, having and M<sup>2</sup> of 1.3. The multipulses consist of user-defined bursts of short pulses, with burst durations ranging from 10ns up to 1000ns, frequencies up to tens of MHz within the burst, with individual pulses in the 10ns to 200ns range and with up to 12kW peak power. Multipulse repetition frequency is controlled externally from single shot up to few MHz, with the possibility of real-time switching between different multipulses.
Dynamic Pulsing is demonstrated using a pulsed MOPA fiber laser at 1064nm. The output of the MOPA laser is a pulsed
profile consisting of a burst of closely spaced pulses. Tests were performed under several materials with pulse bursts
ranging from 10ns to 1μs and operating from 500kHz down to single shot. In particular, percussion drilling in stainless
steel is demonstrated showing improvements in quality and speed of the process. These profiles allow high flexibility
and optimization of the process addressing the specificity of the end application. Dynamic Pulsing allows the same
MOPA fiber laser to be used in diverse materials as well as different processes such us marking, drilling, scribing and
The pulsed fiber laser used in this study is a MOPA-DY by Multiwave Photonics. It is based on a modulated seed laser
followed by a series of fiber amplifiers and ending with an optically isolated collimator. This pulsed laser model has an
output in such a way that each trigger produces a fast burst of pulses, with a repetition frequency within the burst of the
order of tens of MHz. Within the burst it is possible to change the number of pulses, the individual pulse profile, burst
pulse period and even to generate non-periodic burst pulse separations. The laser allows full freedom for all these
combinations. The study here reported compares the impact of pulse peak power, number of pulses within a burst and the
pulse burst period, on process quality (heat affected zone, debris, hole uniformity) and drilling yield.
Pulse bursting is demonstrated using a pulsed MOPA fiber laser at 1064 nm for percussion drilling of stainless steel.
Bursts are configured as fast pulse sequences at tens of MHz, with a temporal envelope in the range from 10 to 420 ns.
Their use rapidly enhances the efficiency of material removal by enhancing pulse energy deposition, and quality
improvement. Results are shown for various pulse conditions by changing number of pulses, spacing and peak powers.
Each pulse burst is collectively triggered and amplified as a single pulse group, at repetition frequencies from singleshot
to hundreds of kHz.
Optical coherence tomography (OCT) imaging at 1060 nm region proved to be a successful alternative in ophthalmology
not only for resolving intraretinal layers, but also for enabling sufficient penetration to monitor the sub-retinal
vasculature in the choroids when compared to most commonly used OCT imaging systems at 800 nm region. To
encourage further clinical research at this particular wavelength, we have developed a compact fiber optic source based
on amplified spontaneous emission (ASE) centered at ~1060 nm with ~70 nm spectral bandwidth at full-width half
maximum (FWHM) and output power >20 mW. Our approach is based on a combination of slightly shifted ASE
emission spectra from a combination of two rare-earth doped fibers (Ytterbium and Neodymium). Spectral shaping and
power optimization have been achieved using in-fiber filtering solutions. We have tested the performances of the source
in an OCT system optimized for this wavelength.