This work reports on a liquid-nitrogen-cooled, SESAM mode-locked Yb:YGAG (Yb:Y(3)Ga(2)Al(3)O(12)) ceramic laser. The Yb:YGAG has a similar structure to Yb:YAG, but its emission spectrum at low ...temperature remains much broader, which is suitable for ultrashort pulse generation and amplification. A stable pulse train with 119-MHz repetition rate was obtained at a wavelength of 1026 nm. The measured pulse duration is 2.4 ps, which is more than four times shorter than that achieved with a cryogenically-cooled Yb:YAG. Furthermore, laser performance of the Yb:YGAG ceramics in continuous-wave operation and wavelength tunability at 80 K was investigated.
The time-resolved measurements of thermally induced wavefront aberrations in a cryogenically cooled Yb:YAG crystal are presented in dependence on temperature in the range between 250 and 130 K under ...non-lasing condition. A wavefront sensor was utilized to determine the wavefront aberrations. The wavefront distortions were experimentally studied for a cryogenically cooled Yb:YAG crystal in detail for the first time. The wavefront aberrations were significantly reduced at cryogenic temperatures including defocus which was the dominant aberration and which was responsible for the so-called thermal lensing effect. We found that defocus aberration is caused not only by thermally induced effects (responsible for thermal lens), but also by electronically induced change in the refractive index due to excitation of ion activators which is responsible for the electronic lensing. Nevertheless, at pumping intensity of 6.3 kW/cm
2
and repetition rate of 100 Hz thermal effects were the dominant one. In addition, an improvement in the Strehl ratio along with an increase in absorbed pump energy was observed while the temperature of the gain medium was decreased. The measurements clearly show the advantages of cryogenic cooling of laser-active media for beam quality improvement.
The goal of the HiLASE project is to design and optimize parameters for 100 J 10 Hz Yb:YAG laser amplifiers that are scalable to the kJ regime. The HiLASE power amplifier design is based on a ...cryogenic, gas-cooled multi-slab concept. Simulation results of the 10 J pre-amplifier agree very well with experimental measurements. In order to fulfil the very demanding requirements, which include wall-plug efficiency > 12% and repetition rates up to 10 Hz, HiLASE and RAL teams are closely working together and developing the approach described here.
We studied the physical effects arising from the combination of several concentrations of luminescent ions, Ho, Tm and Yb in a biaxial crystal to achieve the optimum multicolour emission for cool or ...warm white light generation. White light is generated by the simultaneous emission and combination of three photons at wavelengths, 475 (blue), 542 (green) and 651
nm (red) with associated energies, 21,053
cm
−1, 18,450
cm
−1 and 15,361
cm
−1, respectively. The physical mechanism that generated the white light involved the absorption of infrared photons and after partial energy transfer to neighbouring ions, excited state absorption and upconversion phenomena took place to combine the emerging photons at the above wavelengths. White light is generated with rather high efficiency and very low excitation threshold. The control of simultaneous light generation is accomplished with the amount of dopant ions in the crystal.
► We demonstrated the generation of white light in crystals. ► We grew such crystals at several dopant concentrations. ► We examined the visible luminescence in such crystals. ► We established the optimum dopant concentration for white light generation.
We present measurements of the absorption and emission cross-sections for
Yb:YAG
,
Yb:LuAG
and
Yb:CaF
2
as a function of temperature between 80 and 340 K. The cross-sections are determined by the ...combination of the McCumber relation and the Fuchtbauer–Ladenburg (FL) equation to achieve reliable results in spectral regions of high and low absorption. The experimental setup used for the fluorescence measurements minimizes re-absorption effects due to the measurement from small sample volume, providing nearly undisturbed raw data for the FL approach. The retrieved cross-sections together with the spectral characteristics of the tested materials provide important information for the design of energy efficient, high-power laser amplifiers.
Monoclinic Ho:KY(WO4)2 crystals doped with up to 7.5at.% Ho are grown by the Top Seeded Solution Growth-Slow Cooling method. The evolution of their unit cell parameters in dependence on the Ho doping ...and temperature is studied. The polarized low-temperature (6K) optical absorption of the Ho3+ ion is investigated in detail to determine the energy of the Stark sub-levels. Room-temperature absorption, stimulated-emission and gain cross-section spectra of Ho:KY(WO4)2 crystals are derived for polarizations parallel to the principal optical axes, E||Np, Nm and Ng. The maximum absorption cross-section for the 5I8→5I7 transition is 1.60×10−20cm2 at 1961.0nm and the maximum stimulated-emission cross-section for the 5I7→5I8 transition is 2.65×10−20cm2 at 2056.3nm (for E||Nm). The radiative lifetime of the upper laser level of the Ho3+ ion (5I7) amounts to 4.8ms. Continuous-wave Ho3+ laser operation is achieved under in-band pumping by a Tm laser at 1946nm. In the microchip configuration, the maximum output power reached 205mW at 2105nm with a slope efficiency as high as 85%.
We present the crystal growth, optical spectroscopy, and room temperature continuous-wave (CW) laser operation of monoclinic Ho:KLu(WO
4
)
2
crystals. Macro defect-free crystals of several dopant ...concentrations were grown by top-seeded solution growth slow-cooling method. The evolution of unit cell parameters with holmium doping level and temperature was studied using X-ray powder diffraction. The spectroscopic properties were characterized in terms of room- and low-temperature optical absorption and photoluminescence. From low-temperature optical absorption measurements, the energy of the Stark levels was determined. Calculation of the emission and gain cross sections is presented. CW laser action was realized for 3 and 5 at. % Ho-doped KLu(WO
4
)
2
by in-band pumping using a Tm:KLu(WO
4
)
2
pump laser. A maximum output power of 507 mW with a slope efficiency of ~38 % with respect to the incident power was achieved at 2,080 nm with the Ho:KLu(WO
4
)
2
laser.
We present the crystal growth, optical spectroscopy, and room temperature continuous-wave (CW) laser operation of monoclinic Ho:KLu(WO sub(4)) sub(2) crystals. Macro defect-free crystals of several ...dopant concentrations were grown by top-seeded solution growth slow-cooling method. The evolution of unit cell parameters with holmium doping level and temperature was studied using X-ray powder diffraction. The spectroscopic properties were characterized in terms of room- and low-temperature optical absorption and photoluminescence. From low-temperature optical absorption measurements, the energy of the Stark levels was determined. Calculation of the emission and gain cross sections is presented. CW laser action was realized for 3 and 5 at. % Ho-doped KLu(WO sub(4)) sub(2) by in-band pumping using a Tm:KLu(WO sub(4)) sub(2) pump laser. A maximum output power of 507 mW with a slope efficiency of ~38 % with respect to the incident power was achieved at 2,080 nm with the Ho:KLu(WO sub(4)) sub(2) laser.
We present measurements of the absorption and emission cross-sections for Yb:YAG, Yb:LuAG and Yb:CaF sub(2) as a function of temperature between 80 and 340 K. The cross-sections are determined by the ...combination of the McCumber relation and the Fuchtbauer-Ladenburg (FL) equation to achieve reliable results in spectral regions of high and low absorption. The experimental setup used for the fluorescence measurements minimizes re-absorption effects due to the measurement from small sample volume, providing nearly undisturbed raw data for the FL approach. The retrieved cross-sections together with the spectral characteristics of the tested materials provide important information for the design of energy efficient, high-power laser amplifiers.
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