Ultrafast lasers, which generate optical pulses in the picosecond and femtosecond range, have progressed over the past decade from complicated and specialized laboratory systems to compact, reliable instruments. Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution (much smaller than 10 fs), extremely high peak optical intensities (greater than 10 TW/cm2) and extremely fast pulse repetition rates (greater than 100 GHz).

Recent developments in compact ultrafast lasers

The rise in output power from rare-earth-doped fiber sources over the past decade, via the use of cladding-pumped fiber architectures, has been dramatic, leading to a range of fiber-based devices with outstanding performance in terms of output power, beam quality, overall efficiency, and flexibility with regard to operating wavelength and radiation format. This success in the high-power arena is largely due to the fiber’s geometry, which provides considerable resilience to the effects of heat generation in the core, and facilitates efficient conversion from relatively low-brightness diode pump radiation to high-brightness laser output. In this paper we review the current state of the art in terms of continuous-wave and pulsed performance of ytterbium-doped fiber lasers, the current fiber gain medium of choice, and by far the most developed in terms of high-power performance. We then review the current status and challenges of extending the technology to other rare-earth dopants and associated wavelengths of operation. Throughout we identify the key factors currently limiting fiber laser performance in different operating regimes—in particular thermal management, optical nonlinearity, and damage. Finally, we speculate as to the likely developments in pump laser technology, fiber design and fabrication, architectural approaches, and functionality that lie ahead in the coming decade and the implications they have on fiber laser performance and industrial/scientific adoption.

High power fiber lasers: current status and future perspectives [Invited]

In this Letter we report on the generation of 830 W compressed average power from a femtosecond fiber chirped pulse amplification (CPA) system In the high-power operation we achieved a compressor throughput of about 90% by using high-efficiency dielectric gratings The output pulse duration of 640 fs at 78 MHz repetition rate results in a peak power of 12 MW Additionally, we discuss further a scaling potential toward and beyond the kilowatt level by overcoming the current scaling limitations imposed by the transversal spatial hole burning

Femtosecond fiber CPA system emitting 830 W average output power.

We demonstrate a wideband-tunable Q-switched fiber laser exploiting a graphene saturable absorber. We get ∼2 μs pulses, tunable between 1522 and 1555 nm with up to ∼40 nJ energy. This is a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.

Graphene Q-switched, tunable fiber laser

In this paper, we report 4 different saturable absorbers based on 4 transition metal dichalcogenides (MoS2, MoSe2, WS2, WSe2) and utilize them to Q-switch a ring-cavity fiber laser with identical cavity configuration. It is found that MoSe2 exhibits highest modulation depth with similar preparation process among four saturable absorbers. Q-switching operation performance is compared from the aspects of RF spectrum, optical spectrum, repetition rate and pulse duration. WS2 Q-switched fiber laser generates the most stable pulse trains compared to other 3 fiber lasers. These results demonstrate the feasibility of TMDs to Q-switch fiber laser effectively and provide a meaningful reference for further research in nonlinear fiber optics with these TMDs materials.

Q-switched fiber laser based on transition metal dichalcogenides MoS 2 , MoSe 2 , WS 2 , and WSe 2

A surface-emitting semiconductor laser has been passively mode locked in an external cavity incorporating a semiconductor saturable absorber mirror. The gain medium consists of a stack of 12 InGaAs-GaAs strained quantum wells, grown above a Bragg mirror structure, and pumped optically by a high-brightness diode laser. The mode-locked laser emits pulses of 22-ps full-width at half maximum duration at 1030 nm, with a repetition rate variable around 4.4 GHz.

/pdf/passively-mode-locked-diode-pumped-surface-emitting-b7pg2rt2ba.pdf

Passively mode-locked diode-pumped surface-emitting semiconductor laser

We demonstrate a passively mode-locked diode-pumped thin-disk Yb:YAG laser generating 810-fs pulses at 1030 nm with as much as 60 W of average output power (without using an amplifier). At a pulse repetition rate of 34.3 MHz, the pulse energy is 1.75 µJ and the peak power is as high as 1.9 MW. The beam quality is close to the diffraction limit, with M2<1.1.

/pdf/60-w-average-power-in-810-fs-pulses-from-a-thin-disk-yb-yag-3yyyaaq4wv.pdf

60-W average power in 810-fs pulses from a thin-disk Yb:YAG laser

We demonstrate a passively Q-switched fiber laser system generating pulses with as much as 0.1 mJ pulse energy at 1.53µm and > 1kHz repetition rate. This was achieved with a simple MOPA (master oscillator, power amplifier) scheme with a single pump source, realized with large mode area fiber and multiple reflections on a semiconductor saturable absorber mirror (SESAM).

/pdf/passively-q-switched-0-1-mj-fiber-laser-system-at-1-53-mum-4hbk9vn3xz.pdf

Passively Q-switched 0.1-mJ fiber laser system at 1.53 mum.

We have developed optically pumped passively mode-locked vertical-external-cavity surface-emitting lasers. We achieved as much as 950 mW of mode-locked average power in chirped 15-ps pulses, or 530 mW in 3.9-ps pulses with moderate chirp. Both lasers operate at a repetition rate of 6 GHz and have a diffraction-limited output beam near 950 nm. In continuous-wave operation, we demonstrate an average output power as high as 2.2 W. Device designs with a low thermal impedance and a smooth gain spectrum are the key to such performance. We discuss design and fabrication of the gain structures and, particularly, their thermal properties

/pdf/high-power-passively-mode-locked-semiconductor-lasers-41d1q04zu7.pdf

High-power passively mode-locked semiconductor lasers

We passively Q-switched a diode-pumped Er/Yb:glass microchip laser at a 1.535 μm wavelength using semiconductor saturable absorber mirrors and demonstrated pulses as short as 1.2 ns. By varying the design parameters of the saturable absorber, the pump power, and the pump spot size, we achieved repetition rates from 300 Hz to 100 kHz with pulse energies up to 4 μJ.

https://www.ulp.ethz.ch/content/dam/ethz/special-interest/phys/quantum-electronics/ultrafast-laser-physics-dam/publications_awards/publications/1998/085__APL_72__3273__1998_.pdf

R. Haring

Papers

Passively mode-locked diode-pumped surface-emitting semiconductor laser

60-W average power in 810-fs pulses from a thin-disk Yb:YAG laser

Passively Q-switched 0.1-mJ fiber laser system at 1.53 mum.

High-power passively mode-locked semiconductor lasers

Eyesafe pulsed microchip laser using semiconductor saturable absorber mirrors