Generation of 8–20 μm Mid-Infrared Ultrashort Femtosecond Laser Pulses via Difference Frequency Generation

Abstract

Mid-infrared (MIR) ultrashort laser pulses have a wide range of applications in the fields of environmental monitoring, laser medicine, food quality control, strong-field physics, attosecond science, and some other aspects. Recent years have seen great developments in MIR laser technologies. Traditional solid-state and fiber lasers focus on the research of the short-wavelength MIR region. However, due to the limitation of the gain medium, they still cannot cover the long-wavelength region from 8 to 20 µm. This paper summarizes the developments of 8–20 μm MIR ultrafast laser generation via difference frequency generation (DFG) and reviews related theoretical models. Finally, the feasibility of MIR power scaling by nonlinear-amplification DFG and methods for measuring the power of DFG-based MIR are analyzed from the author’s perspective.

Optical Absorption, Photocarrier Recombination Dynamics and Terahertz Dielectric Properties of Electron-Irradiated GaSe Crystals

“…where ε ∞ is the high-frequency dielectric constant, τ is the momentum relaxation time and c b is the Drude-Smith parameter of backscattering [35], ω Tj is the phonon resonance frequency, ω pj is the phonon resonance amplitude and γ j is the dumping constant. To calculate the model dark and photoexcited total conductivities and the photoexcited carrierinduced complex conductivities, the model dependencies ε phot (ω), ε phot (ω), ε dark (ω) and ε dark (ω), according to (21) with the obtained fitting parameters, were substituted into (17)(18)(19)(20). The model dark and photoexcited complex conductivities of free electrons were calculated using the obtained (during fittings with Equation ( 21)) fitting parameters substituted to the Drude-Smith formula [35]:…”

“…Presently, the main research activity concerns the properties and fabrication of few-layer III-VI structures and their applications in flexible electronics, gas sensors and photodetectors [8,9]. The bulk GaSe crystals have found applications in IR and terahertz nonlinear optics [10][11][12][13][14][15][16][17][18][19][20]. In particular, GaSe has been efficiently used for terahertz generation by optical rectification [11], as well as collinear [12] and noncollinear [14] difference frequency generation.…”

“…In particular, GaSe has been efficiently used for terahertz generation by optical rectification [11], as well as collinear [12] and noncollinear [14] difference frequency generation. These crystals can also be used in terahertz time-domain spectroscopy (THz-TDS) setups as terahertz sensors [15], as well as for broadband mid-IR difference frequency generation [16][17][18] and generation of mid-IR frequency combs [16,19]. Also, this material is demanded in high-repetition-rate optical parametric amplifiers (OPAs) [19,20].…”

Highly efficient, ultra-broadband mid infrared generation driven by a Tm-doped fiber laser system

“…Since these crystals also feature a low bandgap, power scaling so far remained challenging due to high linear and nonlinear absorption of the near infrared driving radiation in these materials. The recent advent of short wavelength infrared driving lasers (1.3 µm -3 µm) sparked a sudden, increasing in conversion efficiency of parametric downconversion due to their lower photon energy, now reaching several percent of conversion efficiency [4,5]. In this contribution, we present our first results on intrapulse difference frequency generation driven by a Thulium (Tm)-doped fiber laser system with large spectral coverage and conversion efficiency paving the way towards W-class laser driven mid infrared sources in the long-wave infrared.…”