Femtosecond Cr²⁺-Based Lasers

Abstract

We review a novel class of femtosecond Cr 2+ -doped ZnSe and ZnS lasers, which operates in a very important for applications wavelength range between 2 and 3.5 μm and which generates ultrashort optical pulses that are only five optical cycles in duration. Room-temperature Cr 2+ -lasers provide tens of Watts average power, >70% slope efficiency, ultrabroad tunability (∼1400 nm between 2 and 3.4 μm) in the continuous wave regime and GW-level peak powers in the amplified femtosecond regime. Different mode-locking techniques from Kerr-lens to graphene saturable absorbers have been demonstrated, and dispersion compensation methods from bulk materials to chirped mirrors allowed the realization of self-starting few-optical cycle oscillators and the demonstration of a number of applications in spectroscopy and nonlinear optics. The Watt level few-optical cycle Cr:ZnS oscillator 1 operating at 2.4 μm is distinguished by extremely short pulse duration of only 41 fs, hundreds of kilowatt peak powers, and tens of nanojoule pulse energies. Using the direct diode-pumping or fiber laser pump sources such a laser can be made reliable and compact, which paves the way to industrial realisation and applications in environmental analysis, oil and gas sensing, hazardous gas detection, breath analysis, fine material processing of semiconductors, composite materials, and glasses.

Gigahertz femtosecond Cr:ZnS laser

“…Though output powers up to 1 W have been demonstrated in mode-locked Cr:ZnS laser [3,4,7,9], operation in the gigahertz regime results in a reduced pulse energies and, thus, requires decreasing of output coupling to keep the intracavity pulse energy at the desirable level. We used an output coupler of 1.8% in this experiment, and the average output power was therefore limited at a 100-mW level.…”

“…The Cr:ZnS femtosecond laser [3] is in many respects analogous to Ti:sapphire with a 3 times longer wavelength centered at 2300-2400 nm, and has been shown to deliver high average power, high-energy pulses [4] of only 5 optical cycles in duration [5], with typical repetition rates of 90-270 MHz [6,7]. Cr:ZnS laser has also shown good performance in combination with a semiconductor saturable absorber mirror [8] and graphene saturable absorber [6].…”

Nonlinear optical response and structural properties of MBE-grown Fe:ZnS films

“…Transition metal substitution in II-VI semiconductors has been a rich area of study for over 50 years [1] but new applications, including dilute magnetic semiconducting devices [2], intermediate band solar cells [3], and mid-infrared lasers [4,5] are driving further development of these materials. In particular, both ZnS and ZnSe have suitable properties as hosts for passive Qswitch and gain species in the mid-infrared region.…”

Coherent octave-spanning mid-infrared supercontinuum generated in As_2S_3-silica double-nanospike waveguide pumped by femtosecond Cr:ZnS laser

“…To extend the spectral broadening further into the mid-IR wavelength range, in the work reported here we have developed a laser based on Cr:ZnS. Indeed, chromium-doped chalcogenide (Cr:ZnS/Cr:ZnSe) based lasers, often called the "Ti-sapphires of the infrared" due to their very broad absorption and emission bands, have recently matured to provide femtosecond performance in all respects comparable with Ti:sapphire lasers [12][13][14]. As such, they represent ideal compact and stable sources for generation of high quality coherent octavespanning supercontinua in the mid-IR.…”