Tapered double-clad fiber: The future of ultrafast high-power laser processing

New fiber technology is poised to provide multikilowatt electricity, ultrashort pulse durations, repetition fees as many as 1 GHz, and significant beam quality in the little package deal.

REGINA GUMENYUK and VALERY FILIPPOV

Ultrafast lasers with pulse durations within the femtosecond and picosecond selection currently engage in a vital function in lots of industrial processes. The value of such lasers for high-quality, practically athermal supplies processing, coupled with innovations in laser technologies, approach advancement, beam dealing with, and shipping, have opened the door for numerous state-of-the-art scientific and industrial applications.

Recent developments employing tapered double-clad fiber (T-DCF) amplifiers now supply the prospect of high electric power with great beam qualities inside a space-effective format and, most remarkably, at generation charges little over regular fibers. What this means is the increasingly essential value for each watt of such ultrafast lasers may possibly be ideally positioned for swift industrial uptake by providing quick financial commitment returns from elevated processing velocity and precision.

The remarkable rise in output electrical power from rare-earth-doped fiber sources over the past decade, through the usage of cladding-pumped fiber architectures such as the NKT Photonics aeroGAIN-ROD,1 has brought about a selection of fiber-based equipment with exceptional efficiency regarding beam excellent, over-all performance, and flexibility in running wavelength and radiation format, with electrical power dealing with beforehand only available in solid-state configurations. Although major innovations in solid-state high-power ultrafast technologies may also be remaining manufactured utilizing new configurations such as Amphos InnoSlab technological know-how, the higher expense of solid-state get materials and thermal administration difficulties should existing significant limitations to its popular adoption.

The eu Fee (EC) funded the pulse job to guidance the development of aggressive technologies that help a lot quicker, extra precise, and nonthermal laser production. Ampliconyx Oy plus the consortium of European associates like Fiat Chrysler are now acquiring a T-DCF laser to provide up to two.5 kW with pulse durations as quick as one hundred fs and repetition prices up to 1 GHz. The entire laser processing technique will take care of high-power ultrashort pulses with scanning hurries up to one.5 km/s utilizing polygon-scanner technological know-how and fiber built-in optics to offer place measurements all the way down to ten μm.

The rise of high-power ultrafast fiber lasers

Ultrafast pulsed lasers have seen exponential growth, using the quantity of filed patents rising fivefold from about a hundred to five hundred for every calendar year. Numerous innovative market programs have benefited from femtosecond laser processing, which includes in photonics, microelectronics, MEMS, and several other markets.

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Fiber, solid-state, and disk lasers tend to be the most promising candidates for high-average-power era. The exceptional features of fiber lasers in contrast to solid-state and disk lasers consist of compactness, robustness, effectiveness, ease of thermal management, and trusted beam excellent. Noticeably decreased manufacturing and routine maintenance charges also make fiber-based ways highly interesting for pico- and femtosecond high-repetition-rate kilowatt-level laser development.

Today’s high-average-power fiber lasers generally use chirped-pulse amplification (CPA). Having said that, in strengthen fiber-based amplifiers, even for hugely stretched pulses the optical peak intensities could become quite superior, producing detrimental nonlinear pulse distortion or maybe destruction on the achieve medium or other optical features. On top of that, other nonlinear consequences this kind of as self-phase modulation, stimulated Raman scattering (SRS), mode instabilities, and inadequate output beam excellent normally crop up in pulsed high-power units limiting their effectiveness.

The primary method of solving troubles for pulsed sign amplification has been to enlarge the main diameter from the fiber. Distinctive energetic fibers with big manner place ended up formulated to extend the surface-to-active-volume ratio of active fibers and, consequently, strengthen heat dissipation and elevate the threshold of nonlinear results enabling power scaling. State-of-the-art high-power fiber-based systems have currently approached >1 kW in the single pulsed amplification channel2 and laid a cornerstone for future ultrashort multikilowatt-level fiber-based laser techniques.

Many varieties of active fibers that has a large successful method location (LMA) have already been produced for prime ability scaling. They're well-known LMA fibers by using a low-aperture core, microstructured rod-type fiber, helical-core or chirally coupled main fibers, and T-DCFs. The mode-field diameter (MFD) achieved with these low-aperture systems normally would not exceed 20-30 μm. The microstructured rod-type fiber incorporates a much larger MFD of as much as sixty five μm and fantastic general performance. Just lately, a powerful 2.2 mJ pulse electricity was shown by a femtosecond learn oscillator electrical power amplifier (MOPA) containing large pitch fiber (LPF).3 On the other hand, LPF fabrication is extremely sophisticated, requiring sizeable processing these types of as precision drilling from the fiber preforms, resulting in bigger generation expenditures. These fibers are also highly sensitive to bending, indicating that attaining satisfactory robustness is usually complicated which fair creation fees are challenging to visualize using LPF.

Conquering nonlinear outcomes in fiber-laser ability scaling
T-DCF is amongst the promising alternatives for high-power fiber-based CPA systems, reducing nonlinear effects when simultaneously simplifying the normal multicascade amplification chain by changing it that has a solitary stage (see Fig. 1). The T-DCF is often a double-clad optical fiber formed working with a specialized fiber drawing process wherein temperature and pulling forces are controlled to type a taper alongside the size in the fiber. By utilizing pre-clad fiber preforms, each the fiber core as well as internal and outer cladding layers change in diameter and thickness alongside the complete size on the fiber. This tapering on the fiber varieties a constant chain of amplifiers with ever-growing core diameter and allows the mixture from the capabilities of standard 8-10 μm diameter double-clad single-mode fibers with individuals of much bigger diameter (50-100 μm) double-clad multimode fibers utilised for high-power amplification.

The results of forming a tapered geometry double-clad fiber is that the light-weight launched into your slim conclude propagates in the huge main devoid of altering the manner material. It's popular that sequentially escalating the diameter of various series of cylindrical optical fiber amplifiers typically improves the threshold of undesired nonlinear consequences. The T-DCF design incorporates this benefit in solitary fiber; like a result, optical amplification maintains fantastic beam top quality by boosting the stimulation thresholds of nonlinear results, like Brillouin and Raman scattering.

Owing to its distinct geometry, the T-DCF know-how can be employed for immediate amplification of large number of the pulsed alerts: with the shorter (several tens of picoseconds) to long (as much as hundreds of nanoseconds) and from slim (some tens of picometers) to broad linewidths (a couple of tens of nanometers). Utilizing tapered fiber with huge conclusion core diameters of approximately two hundred μm by using a 0.eleven numerical aperture (NA), record peak energy and strength amplification concentrations and 60 ps pulses with three hundred μJ electrical power totally free of nonlinear distortions are described.

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The fiber’s double-clad composition signifies that its core can be pumped with larger ability than may be propagated only from the main. The absorption and conversion of pump light-weight for every unit length is greater inside the tapered fiber compared to cylindrical fibers with related concentrations of lively ion doping. This can be due to your improved clad manner mixing as well as better absorption on the thicker conclusion with the taper because of to the a great deal thicker cladding. This also implies which the rare-earth ion dopants are usefully concentrated within the huge finish of a T-DCF, considering that the geometry defines their existence as specifically proportional to your square on the diameter.

Simplicity of production and compactness of assembly

Just one from the most significant advantages of T-DCF is the simplicity of production. The preform output for specific high-power fibers (microstructured rod-type fibers, 3C, or LCFs) entails intricate technologies and stringent structural specifications. In contrast, T-DCF is designed employing typical fiber preforms. Simple creation approaches varying the drawing velocity throughout the pulling method cause the fiber diameter switching alongside its duration. T-DCF output is nearly as simple as the creation of the frequent active fiber. T-DCF fiber might be coiled having a diameter as little as 35 cm, generating a high-power amplifier package deal extremely compact with out degradation of the performance.

The longer term of ultrafast high-power laser processing

The entire laser processing system exploiting all advantages of the T-DCF technologies in combination with novel beam shaping factors, state-of-the-art shipping fiber, and polygon scanner can prevail over the rather extensive processing situations that happen to be an important shortcoming towards the industrial implementation of laser-machining remedies today. These developments through the PULSE consortium is going to be of unique fascination on the automotive sector aiming to cut back car excess weight and accelerate injection-mold texturing or battery creation processes for new electrical cars.

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