Widely tunable narrowband mid-infrared coherent sources, realized using optical parametric oscillators, play an essential role in spectroscopic investigations. A part of mid-infrared spectral region is a “fingerprint range” of solid-state materials, therefore, narrow linewidth is a particularly important feature. The most suitable linewidth of radiation to satisfy the required resolution for spectroscopy of solids is 2‒6 cm-1. The biggest challenge for the developer of the laser source is meeting customers’ needs and providing numerous parameters simultaneously from a single device: broad spectral range, high spectral resolution, fast wavelength tuning, high repetition rate, stable beam direction, nearly diffraction-limited divergence, etc. All this should be provided throughout the entire operational spectral range. These features are relevant for many applications, especially for Scanning Near-field Optical Microscopy (SNOM). This presentation will describe the architecture and applications of EKSPLA's broadly tunable commercial ns and ps laser sources, from 2 to 18 μm based on OP-GaAs fan-type gratings and other mid-infrared OPO nonlinear crystals. The advantages and limitations of the crystals in different narrowband OPO setups will be presented.
A new versatile patent-pending technology enabling new operation regimes and a unique set of features in the industrialgrade 30 W-level average power femtosecond hybrid laser is introduced in this work. The developed technology, based on the use of an all-in-fiber active fiber loop (AFL), enabled to form GHz bursts of ultrashort laser pulses with any desired pulse repetition rate and any number of pulses in a burst with identical intra-burst pulse separation. Furthermore, the AFL allowed to tune pulse duration from a few hundred femtoseconds to picoseconds and even up to the nanosecond range.
We demonstrated a 100 W class hybrid laser system based on fiber seed laser and two free-space end-pumped Yb:YAG amplifiers capable of delivering record high pulse energy in a rod-type active medium setup operating at room temperature. The achieved output pulse energy was <10 mJ at 10 kHz pulse repetition rate. The output pulses of 1.09 ps duration were close to Fourier transform-limit. The output beam quality remained high (M2 < 1.3) despite being affected by thermally induced stress in the gain medium.
In this work we present a novel concept of compact broadband high resolution sum frequency generation spectroscopy system. Multiple channel picosecond fiber laser was used as a seed for narrowband (~1.5 cm-1 ) and broadband ultrafast radiation sources. In order to achieve >500 cm-1 linewidth widely tunable microjoule-level pulses in MIR spectral region (2 - 10 μm) broadband femtosecond source optimization was performed. Numerical simulations of various schemes with different nonlinear crystals and experimental results were presented and compared.
In this work we presented a compact femtosecond high average power (35 W), high energy (35 uJ) and high pulse repetition rate (1 MHz) laser system based on efficient room-temperature Yb:YAG crystal rod double-pass power amplifier and Yb doped fiber seed laser. High fidelity nearly transform-limited pulses (330 fs) were obtained by using matched dispersion pair of chirped fiber Bragg grating (CFBG) as a pulse stretcher and 4-pass diffraction grating based pulse compressor. Residual dispersion mismatch was compensated by applying linear thermal gradient along CFBG. Presented laser system is a compact and convenient solution for various industrial and scientific applications.
A compact high-power femtosecond (~640 fs) GHz intra-burst repetition rate all-in-fiber CPA system operating at 3.26 GHz intra-burst and 200 kHz burst repetition rate regime with two configurations of large mode area (LMA and PCF) cladding-pumped Yb-doped fiber power amplifiers were presented in this work. Significantly high average power levels of 6 W (LMA fiber power amplifier) and <20 W (PCF power amplifier) were achieved which corresponded to a maximum energy of 30 μJ and <100 μJ per burst respectively. Two burst shaping layouts were introduced in this experimental setup obtaining desired burst shape using one or two acousto-optic modulators, pulse repetition rate multiplier based on a cascaded 2×2 fiber coupler sequence with a splitting ratio of 50/50 and controlled using arbitrary waveform generator. High power all-in-fiber CPA system with LMA fiber power amplifier operating at GHz burst regime was compared to the system operating at MHz pulse repetition rate regime which allowed to achieve 1.5 μJ energy pulses of good pulse quality at the output of the laser system at a repetition rate of 4 MHz.
A novel chirped pulse amplification (CPA) configuration consisting of chirped fiber Bragg grating (CFBG) with tunable dispersion as a pulse stretcher and chirped volume Bragg grating (CVBG) as a pulse compressor is presented. We demonstrated that ultra short pulses was stretched up to 300 ps and compressed to sub-1ps without residual pedestal using described configuration quite efficiently.
We report results of design and optimization of high average power picosecond and nanosecond laser operating at 1342 nm wavelength. This laser is comprised of master oscillator, regenerative amplifier and output pulse control module. Passively mode-locked Nd:YVO4 master oscillator emits ~ 10 ps pulses at repetition rate of 55 MHz with average output power of ~ 100 mW. These pulses were used to seed regenerative amplifier based on composite diffusion-bonded Nd:YVO4 rod with variable Nd doping concentration pumped at 880 nm wavelength. Laser produces 10.9 ps pulses at 300 kHz repetition rate with average output power of 11 W and nearly diffraction limited beam quality M2 ~ 1.03. Fraction of laser output was converted to the second harmonics with 60 % efficiency providing the average power of 5 W at 671 nm wavelength. Without seeding the regenerative amplifier transforms to electro-optically cavitydumped Q-switched laser delivering 10 ns pulses at high repetition rates with beam propagation factor of M2 ~ 1.06.
In this work we present a beam shaping technique based on a spatially variable phase retardation plate inscribed inside bulk of fused silica glass by femtosecond laser pulses. Formation of self-assembled periodic nanostructures was exploited to fabricate the converter. During the fabrication process we control induced nanogratings orientation and retardance. Combination of a spatially variable waveplate and a polarizer acts as a spatially variable transmission filter. With a converter fabricated to transform an initially Gaussian beam to a flat-top beam we preserve more than 50% of initial laser power. Theoretically, the efficiency of the proposed converter could be up to 70%. The proposed converter with no absorbing elements possesses resistance to optical damage similar to that of fused silica. Additionally, the already-fabricated converter allows for on-the-fly adjustment of the beam shape from flat-top to a shape with a dip in the middle. The shaped beam was tested in a high power picosecond pulse amplifier.
We demonstrate results of design and optimization of high average output power picosecond laser operating at 1342 nm wavelength for selective material processing. This laser is comprised of mode locked master oscillator, regenerative amplifier and output pulse control module. Passively mode locked by means of semiconductor saturable absorber and pumped with 808 nm wavelength Nd:YVO4 master oscillator emits pulses of ~ 13 ps duration at repetition rate of 55 MHz with average output power of ~ 140 mW. The four-pass confocal delay line with image relay forms a longest part of the oscillator cavity in order to suppress thermo-mechanical misalignment. Optimization of the intracavity pulse fluence ensures significant lifetime improvement for the saturable absorber. This oscillator was used as the seeder for regenerative amplifier based on composite diffusion-bonded Nd:YVO4 rod pumped with 880 nm wavelength. When operating at 300 kHz repetition rate the laser delivers high quality output beam of M2 ~ 1.1 with average power in excess of 10 W at 1342 nm wavelength.
We present results of beam quality investigation in Nd:YAG crystal fiber amplifier seeded by ns, sub-ns and ps laser
pulses counter-propagating to continuous pump of < 110 W power at 808 nm wavelength. The maximum amplified
power of 44 W and energy of 3.2 mJ has been achieved with ns seed. We observed gain rise to < 75 with ps seed of
1.6 mW average power when tuned emission spectra to ~ 1064.3 nm. Beam propagation coefficient M2 approach 1.2 at
the maximum pump power with high quality seed pulse emitted by 6 ps fiber laser. Amplification of sub-ns seed pulses
from microchip laser led to an M2 increase from ~1.2 to ~< 1.5. New analytical solution for temperature distribution in
end-pumped thin long single crystal fiber with temperature dependent thermal conductivity coefficient is found for
polynomial transverse pump distribution. The analytical relation between thermal coefficients of refractive index at zero
stresses and zero strains is found for YAG type cubic crystals. Using plane strain approximation the analytical expression
for thermal radial and tangential changes of refractive index is found, and the relation between different expressions for
so-called photoelastic constants Cr,θ is established. The methods of numerical calculation of rays and Gaussian beam
propagation in a graded-index medium of active element are developed. The error in widely used formula for M2 of
Gaussian beam with quartic phase aberration is corrected. It is shown that beam quality degradation can be explained by
active thermal lens in power amplifier when changes of transverse beam shape or beam width during amplification are
taken into account.
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