Process limits for percussion drilling of stainless steel with ultrashort laser pulses at high average powers

The availability of commercial ultrafast lasers reaching into the kW power level offers promising potential for high-volume manufacturing applications. Exploiting the available average power is challenging due to process limits imposed by particle shielding, ambient atmosphere breakdown, and heat accumulation effects. We experimentally confirm the validity of a simple thermal model, which can be used for the estimation of a critical heat accumulation threshold for percussion drilling of AISI 304 steel. The limits are summarized in a processing map, which provides selection criteria for process parameters and suitable lasers. The results emphasize the need for process parallelization.

Throughput scaling by spatial beam shaping and dynamic focusing

With availability of high power ultra short pulsed lasers, one prerequisite towards throughput scaling demanded for industrial ultrafast laser processing was recently achieved. We will present different scaling approaches for ultrafast machining, including raster and vector based concepts. The main attention is on beam shaping for enlarged, tailored processed volume per pulse. Some aspects on vector based machining using beam shaping are discussed. With engraving of steel and full thickness modification of transparent materials, two different approaches for throughput scaling by confined interaction volume, avoiding detrimental heat accumulation, are exemplified. In Contrast, welding of transparent materials based on nonlinear absorption benefits from ultra short pulse processing in heat accumulation regime. Results on in-situ stress birefringence microscopy demonstrate the complex interplay of processing parameters on heat accumulation. With respect to process development, the potential of in-in-situ diagnostics, extended to high power ultrafast lasers and diagnostics allowing for multi-scale resolution in space and time is addressed.

All-fiber ultrafast amplifier at 1.9 μm based on thulium-doped normal dispersion fiber and LMA fiber compressor

The duration reduction and the peak power increase of ultrashort pulses generated by all-fiber sources at a wavelength of $$1.9\,\upmu \hbox {m}$$ 1.9 μ m are urgent tasks. Finding an effective and easy way to improve these characteristics of ultrafast lasers can allow a broad implementation of wideband coherent supercontinuum sources in the mid-IR range required for various applications. As an alternative approach to sub-100 fs pulse generation, we present an ultrafast all-fiber amplifier based on a normal-dispersion germanosilicate thulium-doped active fiber and a large-mode-area silica-fiber compressor. The output pulses have the following characteristics: the central wavelength of $$1.9\,\upmu \hbox {m}$$ 1.9 μ m , the repetition rate of 23.8 MHz, the energy per pulse period of 25 nJ, the average power of 600 mW, and a random output polarization. The pulse intensity and phase profiles were measured via the second-harmonic-generation frequency-resolved optical gating technique for a linearly polarized pulse. The linearly polarized pulse has a duration of 71 fs and a peak power of 128.7 kW. The maximum estimated peak power for all polarizations is 220 kW. The dynamics of ultrashort-pulse propagation in the amplifier were analyzed using numerical simulations.

Synchronized multi-wavelength soliton fiber laser via intracavity group delay modulation

Locking of longitudinal modes in laser cavities is the common path to generate ultrashort pulses. In traditional multi-wavelength mode-locked lasers, the group velocities rely on lasing wavelengths due to the chromatic dispersion, yielding multiple trains of independently evolved pulses. Here, we show that mode-locked solitons at different wavelengths can be synchronized inside the cavity by engineering the intracavity group delay with a programmable pulse shaper. Frequency-resolved measurements fully retrieve the fine temporal structure of pulses, validating the direct generation of synchronized ultrafast lasers from two to five wavelengths with sub-pulse repetition-rate up to ~1.26 THz. Simulation results well reproduce and interpret the key experimental phenomena, and indicate that the saturable absorption effect automatically synchronize multi-wavelength solitons in despite of the small residual group delay difference. These results demonstrate an effective approach to create synchronized complex-structure solitons, and offer an effective platform to study the evolution dynamics of nonlinear wavepackets.

The challenges of productive materials processing with ultrafast lasers

Materials processing with ultrafast lasers with pulse durations in the range between about 100 fs and 10 ps enable very promising and emerging high-tech applications. Moreover, the average power of such lasers is steadily increasing; multi kilowatt systems have been demonstrated in laboratories and will be ready for the market in the next few years, allowing a significantly increase in productivity. However, the implementation of ultrafast laser processes in applications is very challenging due to fundamental physical limitations. In this paper, the main limitations will be discussed. These include limitations resulting from the physical material properties such as the ablation depth and the optimal fluence, from processing parameters such as air-breakdown and heat accumulation, from the processing system such as thermal focus shift, and from legal regulations due to the potential emission of soft X-rays.

SESAM Mode-Locked Yb:Ca3Gd2(BO3)4 Femtosecond Laser

We report on the first passively mode-locked femtosecond-laser operation of a disordered Yb:Ca3Gd2(BO3)4 crystal using a SEmiconductor Saturable Absorber Mirror (SESAM). Pumping with a single-transverse mode fiber-coupled laser diode at 976 nm, nearly Fourier-transform-limited pulses as short as 96 fs are generated at 1045 nm with an average output power of 205 mW and a pulse repetition rate of ~67.3 MHz. In the continuous-wave regime, high slope efficiency up to 59.2% and low laser thresholds down to 25 mW are obtained. Continuous wavelength tuning between 1006–1074 nm (a tuning range of 68 nm) is demonstrated. Yb:Ca3Gd2(BO3)4 crystals are promising for the development of ultrafast lasers at ~1 μm.

Light People: Professor John Dudley spoke about supercontinuum generation and International Day of Light

EditorialThe extreme spectral broadening of light in supercontinuum generation (SCG) is considered by many as the ultimate legacy of nonlinear optics. In this interview, Light: Science & Applications invited John Dudley [see the “Short Bio” section]—pioneer of supercontinuum generation, rogue waves, and ultrafast lasers—to share insight on how supercontinuum generation have evolved over the past decades and where it is heading. Also as the Steering Chair of UNESCO’s International Day of Light & International Year of Light (IDL & IYL), John is asked to share his comments on how light may influence post-pandemic World.

PbS Quantum Dots Saturable Absorber for Dual-Wavelength Solitons Generation

PbS quantum dots (QDs), a representative zero-dimensional material, have attracted great interest due to their unique optical, electronic, and chemical characteristics. Compared to one- and two-dimensional materials, PbS QDs possess strong absorption and an adjustable bandgap, which are particularly fascinating in near-infrared applications. Here, fiber-based PbS QDs as a saturable absorber (SA) are studied for dual-wavelength ultrafast pulses generation for the first time to our knowledge. By introducing PbS QDs SA into an erbium-doped fiber laser, the laser can simultaneously generate dual-wavelength conventional solitons with central wavelengths of 1532 and 1559 nm and 3 dB bandwidths of 2.8 and 2.5 nm, respectively. The results show that PbS QDs as broadband SAs have potential application prospects for the generation of ultrafast lasers.