Kerr-lens mode-locked Cr:ZnS oscillator reaches the spectral span of an optical octave

High-power, gigahertz repetition frequency self-mode-locked Ho:GdVO4 laser resonantly pumped by a Tm-doped fiber laser

A self-mode-locked Ho:GdVO4 laser with the GHz pulse repetition frequency oscillation near 2.06 µm was demonstrated for the first time to our knowledge. The output performances of the self-mode-locked Ho:GdVO4 laser were investigated for a few output coupler transmittances at the pulse repetition frequency of 1.89 GHz. At the incident pump power of 8.12 W, the maximum average output power was as high as 2.28 W, corresponding to the slope efficiency and optical-to-optical efficiency of 36.3% and 28.1%, respectively. This is the maximum average output for the 2 µm self-mode-locked solid-state laser with a GHz pulse repetition frequency. This work provides a new way for generating an efficient and a high-power ultrafast pulse laser with a GHz repetition frequency in the 2 µm wave band.

Atmospheric dispersion management in mid-IR mode-locked oscillators

The atmospheric dispersion in the mid-infrared transparency windows presents an important albeit often neglected factor when developing ultrashort-pulsed lasers. We show that it can amount to hundreds of fs² in 2-3 µm window with typical laser round-trip path lengths. Using the Cr:ZnS ultrashort-pulsed laser as a test-bed, we demonstrate the atmospheric dispersion influence on femtosecond and chirped-pulse oscillator performance and show that the humidity fluctuations can be compensated by an active dispersion control, greatly improving stability of mid-IR few-optical cycle laser sources. The approach can be readily extended to any ultrafast source in the mid-IR transparency windows.

Nonlinear pulse compression to sub-two-cycle, 1.3 mJ pulses at 1.9 μm wavelength with 132 W average power

We report the nonlinear pulse compression of a high-power, thulium-doped fiber laser system using a gas-filled hollow-core fiber. The sub-two cycle source delivers 1.3 mJ pulse energy with 80 GW peak power at a central wavelength of 1.87 μm and an average power of 132 W. This is, so far, to the best of our knowledge, the highest average power of a few-cycle laser source reported in the short-wave infrared region. Given its unique combination of high pulse energy and high average power, this laser source is an excellent driver for nonlinear frequency conversion, toward terahertz, mid-infrared, and soft X-ray spectral regions.

8.7-W average power, in-band pumped femtosecond Ho:CALGO laser at 2.1 µm

We report on an in-band pumped SESAM mode-locked Ho:CALGO bulk laser with a record-high average power of 8.7 W and an optical-to-optical efficiency of 38.2% at a central wavelength of 2.1 µm. At this power level, the bulk laser generates pulses with a duration of 369 fs at an 84.4-MHz repetition rate, corresponding to a pulse energy of 103 nJ and a peak power of 246 kW. To the best of our knowledge, this is the highest average power and pulse energy directly generated from a mode-locked bulk laser in the 2-3 µm wavelength region. Our current results indicate that Ho:CALGO is a competitive candidate for average power scaling of 2-µm femtosecond lasers.

Second and third-order dispersion compensating mirror pairs for the spectral range from 1.2-3.2µm

We demonstrate the design, production, characterization and application of two dispersive complementary mirror pairs compensating second- and third-order dispersion, respectively. Both mirror pairs operate in the spectral range from 1.2-3.2µm. This is an unprecedented bandwidth of over 1.4 octaves which can drive further improvements in Cr:ZnS, Cr:ZnSe and other laser systems with a central wavelength around 2µm. The first pair provides a constant group delay dispersion of -100fs², while the second one enables the compensation of the third-order dispersion that is introduced by a TiO₂ crystal.

Ultrafast Tm-doped fiber laser system delivering 1.65-mJ, sub-100-fs pulses at a 100-kHz repetition rate

High-energy, ultrafast, short-wavelength infrared laser sources with high average power are important tools for industrial and scientific applications. Through the coherent combination of four ultrafast thulium-doped rod-type fiber amplifiers, we demonstrate a Tm-doped chirped pulse amplification system with a compressed pulse energy of 1.65 mJ and 167 W of average output power at a repetition rate of 101 kHz. The system delivers 85 fs pulses with a peak power of 15 GW. Additionally, the system presents a high long- and short-term stability. To the best of our knowledge, this is the highest average output power short wavelength IR, mJ-class source to date. This result shows the potential of coherent beam combining techniques in the short wavelength infrared spectral region for the power scalability of these systems.

Inherent intensity noise suppression in a mode-locked polycrystalline Cr:ZnS oscillator

We developed a diode-pumped, mode-locked polycrystalline Cr:ZnS oscillator using single-walled carbon nanotubes as a saturable absorber. The oscillator exhibits self-start mode-locking operation, generating sub-100 fs pulses with an average power of 300 mW. We found a unique feature in which the intensity noise originating from relaxation oscillation is suppressed by inherent second harmonic generation in polycrystalline Cr:ZnS. The observed noise suppression is reproduced by a theoretical model that includes an instantaneous nonlinear loss.