High-repetition rate, mid-infrared, picosecond pulse generation with µJ-energies based on OPG/OPA schemes in 2-µm-pumped ZnGeP2.

We report on two different concepts to generate µJ-level mid-infrared laser pulses with sub-10 ps pulse duration via nonlinear parametric generation at high pulse repetition rates. Both schemes rely on the recent development of compact and efficient CPA-free, Ho:YLF-based 2-µm laser sources pumping the highly nonlinear crystal ZnGeP2 used for parametric amplification. The first concept comprises a simplified OPG/OPA scheme efficiently producing signal and idler radiation at fixed wavelengths of 3.0 and 6.5 µm, respectively. In the second concept, we demonstrate a wide spectral tunability of the picosecond, µJ pulses over the entire tuning range between 2.5 and 12 µm maintaining a constant bandwidth of sub-20 cm-1 by integrating a two-color pumping scheme and a spectral shaper into the setup. The presented compact and efficient mid-IR picosecond radiation sources offer a way towards low-cost mid-IR material processing and spectroscopic applications.

Mode-locked pulses from a Thulium-doped fiber Mamyshev oscillator.

We present experimental results of the generation of ultrashort pulses in the 2 µm wavelength region by a fiber Mamyshev oscillator, along with the simulation of the pulse propagation in the cavity. The Mamyshev oscillator emitted pulses with energies of 3.55 nJ at a repetition rate of 15 MHz and optical spectra with bandwidths of 48 nm. The pulses propagated in anomalous dispersive Thulium-doped fiber sections with dispersion compensation sections of normal dispersive fibers.

Sub-50 fs, µJ-level pulses from a Mamyshev oscillator-amplifier system.

In this Letter, we present a Mamyshev oscillator with an output power of 332 mW and a pulse energy of 31 nJ, which is directly amplified in an additional fiber section. By balancing the gain-narrowing effect with self-phase modulation during the amplification, we achieved an average output power of 11 W, corresponding to a pulse energy of more than 1 µJ. The pulse duration can be compressed to sub-50 fs behind the amplification stage.

Millijoule-level, kilohertz-rate, CPA-free linear amplifier for 2 µm ultrashort laser pulses.

The generation of millijoule-level ultrashort laser pulses at a wavelength of 2.05 µm in a compact chirped pulse amplification-free linear amplifier based on Holmium-doped YLF gain medium is presented. More than 100 MW of pulse peak power has been achieved. We show the capabilities of this laser amplifier from a 1 kHz to 100 kHz repetition rate. A detailed numerical description supports the experimental work and verifies the achieved results.

High repetition rate, µJ-level, CPA-free ultrashort pulse multipass amplifier based on Ho:YLF.

We report on CPA-free multipass amplification of ps-pulses in Holmium-doped yttrium lithium fluoride (Ho:YLF) crystals up to µJ pulse-energy-covering repetition rates from 10 kHz up to 500 kHz. The seed pulses at a wavelength of 2.05 µm are provided by a Ho-based all-fiber system consisting of a soliton oscillator and a subsequent pre-amplifier followed by a free-space AOM as pulse-picker. Considering the achieved pulse peak power at MW-level, this system is a powerful tool for efficient pumping of parametric conversion stages addressing the highly demanded mid-IR spectral region.

Mode-locked Ho-doped laser with subsequent diode-pumped amplifier in an all-fiber design operating at 2052 nm.

We present a mode-locked holmium-doped all-fiber soliton laser operating in the 2052 nm wavelength range. The ultrashort pulse oscillator is simultaneously self-providing 1950-nm radiation for efficient in-band pumping in a subsequent thulium-/holmium-doped fiber tandem amplifier. More than 76 nJ-pulses for Ho:YLF or Ho:YVO4 amplifier seeding have been achieved.

Comparison between Tm:YAP and Ho:YAG ultrashort pulse regenerative amplification.

We compare the performance characteristics of Tm:YAP and Ho:YAG in ultrashort pulse regenerative amplification. Both systems follow the same amplification concept and use nearly the same experimental setup reaching similar output energies of >700 µJ.

700 MW peak power of a 380 fs regenerative amplifier with Tm:YAP.

We report on a high power ultrashort pulse regenerative amplifier system, entirely based on thulium-doped laser materials operating around 1.94 µm. At a repetition rate of 1 kHz the Tm:YAP regenerative amplifier emits pulse energies > 700 µJ, only limited by the damage threshold of the Tm:YAP crystal. The pulses can be compressed to 380 fs at an efficiency of 50 %. Purging of the regenerative amplifier cavity with nitrogen is necessary due to atmospheric absorptions causing long ps pedestals in the autocorrelation.

152 W average power Tm-doped fiber CPA system.

A high-power thulium (Tm)-doped fiber chirped-pulse amplification system emitting a record compressed average output power of 152 W and 4 MW peak power is demonstrated. This result is enabled by utilizing Tm-doped photonic crystal fibers with mode-field diameters of 35 µm, which mitigate detrimental nonlinearities, exhibit slope efficiencies of more than 50%, and allow for reaching a pump-power-limited average output power of 241 W. The high-compression efficiency has been achieved by using multilayer dielectric gratings with diffraction efficiencies higher than 98%.

Ultrafast, stretched-pulse thulium-doped fiber laser with a fiber-based dispersion management.

An ultrafast thulium-doped fiber laser with stretched-pulse operation has been realized and investigated. The passively mode-locked oscillator emitted 119 fs pulses at a peak wavelength of 1912 nm. A normal-dispersion fiber with a high numerical aperture and small core was used for intracavity dispersion management and external compression. Numerical simulations were performed and are in good agreement with the experimental results.

Monotonically chirped pulse evolution in an ultrashort pulse thulium-doped fiber laser.

We report on monotonically positively chirped pulse operation of a hybridly mode-locked thulium fiber laser. Dispersion management was realized with a small-core, high-NA fiber providing normal dispersion in the 2 µm wavelength region. The laser delivered pulses with 0.7 nJ energy at the 1927 nm center wavelength and sub-500-fs pulse duration after compression.

Pulse duration and energy scaling of femtosecond all-normal dispersion fiber oscillators.

We investigate the scaling properties of mode-locked all-normal dispersion fiber oscillators in terms of output pulse energy and compressed pulse duration. Experimental results are achieved by stepwise variation of the resonator dispersion, total fiber length, and the spectral filter bandwidth. Adjustment of these parameters enables pulse duration scaling down to 31 fs and increase of output pulse energy up to 84 nJ.

0.5 µJ pulses from a giant-chirp ytterbium fiber oscillator.

We present a mode-locked all-normal dispersion ytterbium fiber oscillator with output pulse energies beyond 0.5 µJ. The oscillator is mode-locked using nonlinear polarization rotation, and stable single-pulse operation is achieved by spectral filtering inside the resonator. The oscillator generates strongly chirped output pulses at a repetition rate of 4.3 MHz which can be compressed down to 760 fs.

Sub-80-fs pulses from an all-fiber-integrated dissipative-soliton laser at 1 µm.

We report on a passively mode-locked femtosecond fiber oscillator using only fiber-based components without intracavity dispersion compensation. The all-normal dispersion fiber laser operates in the dissipative-soliton regime and utilizes a spectral filter for pulse shaping. The 3.8 ps long pulses with pulse energies of 3.6 nJ can be dechirped with a grating compressor to 76 fs. The output spectrum reveals a full width at half maximum of 39.7 nm and a center wavelength of 1032 nm. The repetition rate is 71 MHz. The influence of pulse energy variation is discussed.

Pulse characteristics of a passively mode-locked thulium fiber laser with positive and negative cavity dispersion.

We investigated of the output characteristics of a spectrally filtered stretched-pulse thulium fiber laser in dependence of cavity dispersion and pump power. The experimental results together with corresponding theoretical modeling allow for a deeper insight into the pulse shaping mechanisms.

Pulse energy of 151 nJ from ultrafast thulium-doped chirped-pulse fiber amplifier.

We report on chirped-pulse amplification of an ultrafast thulium-doped fiber laser. Pulses with an energy of 3.3 nJ and a bandwidth-limited pulse duration of 195 fs could be amplified to 151 nJ, which corresponds to an average power of 5.7 W at 37.6 MHz pulse repetition rate. The maximum output power was limited by the available pump power. The pulses could be dechirped to a duration of 258 fs.

50 fs pulses from an all-normal dispersion erbium fiber oscillator.

We present a mode-locked, all-normal-dispersion erbium-doped fiber oscillator generating output pulses with broadband spectra covering the range from 1475 to 1620 nm. The oscillator operates at a repetition rate of 109 MHz with output pulse energies of 1.6 nJ. Mode-locked operation is achieved by use of nonlinear polarization evolution in combination with a birefringent filter. The output pulses are dechirped with an external prism compressor to a duration of 50 fs.

High-power dissipative solitons from an all-normal dispersion erbium fiber oscillator.

We demonstrate output pulse energies of 20 nJ from an erbium-doped fiber oscillator that contains only positive dispersion fibers and is mode locked by use of nonlinear polarization evolution and stabilized with a birefringent filter. The fiber oscillator operates at a repetition rate of 3.5 MHz with a central wavelength of 1550 nm. The positively chirped output pulses have a duration of 53 ps and are compressed to 750 fs. The large positive chirp of the output pulses and the steep side edges of the pulse spectrum indicate dissipative soliton operation.

Regenerative thin disk amplifier with combined gain spectra producing 500 microJ sub 200 fs pulses.

An Yb:KYW femtosecond regenerative amplifier with combination of two gain spectra from a single thin disk is presented. The amplifier generated an average power of 10 W after compression at a repetition rate of 20 kHz resulting in a pulse energy of 500 microJ. A bandwidth of 18.6 nm at -20 dB allowed a compression to nearly Fourier-limited pulses with a duration of 185 fs resulting in a peak power of 2.7 GW.

Spatially dispersive regenerative amplification of ultrashort laser pulses.

A novel CPA-system with a spatially dispersive Yb:KYW-based regenerative amplifier is presented. Three prisms inside the amplifier divide the seed pulses from an Yb fiber laser system into spatially separated spectral components that pass through different volumes of the active medium and are amplified independently. This concept allows overcoming the effect of gain-narrowing. The spatially dispersive amplifier delivers laser pulses with energies of up to 30 microJ at a repetition rate of 100 kHz. Successful compression of the amplified pulses down to 171 fs is demonstrated.