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.

Efficient high-energy Raman soliton generation in a Tm:doped large mode area fiber amplifier.

We report the Tm-doped all-fiber MOPA based on a LMA active fiber generating Raman solitons tunable in the range 1970-2300 nm directly from the LMA fiber. By tuning the chirp of the input pulse we reached more than 90 % energy transfer efficiency to Raman soliton. Solitons with 125 fs duration and up to 24 nJ energy are demonstrated in LMA fiber amplifier. We show experimentally that Raman solitons experience both amplification and absorption in active fiber components of the laser system and that the energy of a Raman soliton generated in an LMA fiber amplifier is limited by the soliton area theorem.

Coherent octave-spanning mid-infrared supercontinuum generated in As2S3-silica double-nanospike waveguide pumped by femtosecond Cr:ZnS laser.

A more than 1.5 octave-spanning mid-infrared supercontinuum (1.2 to 3.6 µm) is generated by pumping a As2S3-silica "double-nanospike" waveguide via a femtosecond Cr:ZnS laser at 2.35 µm. The combination of the optimized group velocity dispersion and extremely high nonlinearity provided by the As2S3-silica hybrid waveguide enables a ~100 pJ level pump pulse energy threshold for octave-spanning spectral broadening at a repetition rate of 90 MHz. Numerical simulations show that the generated supercontinuum is highly coherent over the entire spanning wavelength range. The results are important for realization of a high repetition rate octave-spanning frequency comb in the mid-infrared spectral region.

Graphene mode-locked Cr:ZnS laser with 41 fs pulse duration.

We report the ultrashort-pulse Cr:ZnS laser mode-locked by graphene-based saturable absorber mirror. Using the combination of bulk material and a chirped mirror, we demonstrate the shortest reported so far mid-IR pulses of only 5.1 optical cycles (41 fs) centered at 2.4 µm with 190 nm spectral bandwidth. The pulse spectrum almost completely fills the water-free atmospheric window. The output parameters reach 2.3 nJ pulse energy and 250 mW average output power at 108 MHz repetition rate.

Graphene mode-locked Cr:ZnS chirped-pulse oscillator.

We report the first to our knowledge high-energy graphene mode-locked solid-state laser operating in the positive dispersion regime. Pulses with 15.5 nJ energy and 42 nm spectral bandwidth with 0.87 ps duration were obtained at 2.4 µm wavelength. The output can be compressed down to 189 fs. The graphene absorber damage threshold was established at fluence approaching 1 mJ/cm².

Kerr-lens mode-locked Cr:ZnS laser.

We report the soft-aperture Kerr-lens mode-locked Cr:ZnS laser, generating 550 mW of 69 fs nearly transform-limited pulses at 2.39 µm wavelength. The pulse energy reached 3.8 nJ at 145 MHz repetition rate, limited by the onset of double-pulsing. This corresponds to the shortest-pulse and highest-energy direct femtosecond laser source in the mid-infrared. Dispersion compensation was achieved by a single chirped mirror and a thin sapphire plate, making the laser design simple, compact and very stable, and operating at ambient air and room temperature. The superb thermal and mechanical properties of Cr:ZnS, exceeding those of Cr:ZnSe and many established femtosecond laser crystals, should allow for further scaling of output power.

Chaotic chirped-pulse oscillators.

We present results of experimental investigation of the chaotic and quasi-periodic regime in the chirped-pulsed (dissipative soliton) Cr:ZnS and Cr:ZnSe mid-IR oscillators with significant third-order dispersion. The instability develops when the spectrum edge approaches resonance with a linear wave either due to power increase or by dispersion adjustment. In practice, this occurs when the spectrum edge reaches zero dispersion wavelength. The analysis suggests a three-oscillator chaos model, which is confirmed by numerical simulations. The regime is long-term stable and can be easily overlooked in similar systems. We show that chaotic regime is accompanied by a characteristic spectral shape and can be reliably recognized by using wavelength-skewed filters and by second-harmonic or two-photon absorption detectors.

Femtosecond SESAM-modelocked Cr:ZnS laser.

We report self-starting femtosecond operation of a 180-MHz SESAM-controlled prismless Cr:ZnS laser around 2400 nm at open air and room temperature. Dispersion compensation was achieved by a combination of bulk materials and chirped mirrors. Both soliton- and chirped-pulse operation regimes have been demonstrated with 130 fs (630 fs) pulse duration at 130 (205) mW average output power, respectively. The output power was about 30% higher than for a comparable Cr:ZnSe sample in the same cavity.

Efficient 1 W continuous-wave diode-pumped Er,Yb:YAl3(BO3)4 laser.

We report the spectroscopy and high-power continuous-wave (CW) diode-pumped laser operation of Er:Yb:YAl3(BO3) crystal. Absorption and stimulated emission spectra, emission lifetimes, and efficiency of energy transfer from Yb3+ to Er3+ ions were determined. A CW Er:Yb:YAB laser emitting at 1602, 1555, and 1531 nm with output power as high as 1W and slope efficiency up to 35% was demonstrated.