Gadolinium scandium aluminum garnet scintillator crystals (GSAG:Ce) with Ca2+, Mg2+, and Li+ co‐d... more Gadolinium scandium aluminum garnet scintillator crystals (GSAG:Ce) with Ca2+, Mg2+, and Li+ co‐dopants are grown by the Bridgman method under reducing atmosphere. Crystals are irradiated with a 60Co gamma‐ray source to 10 kGy and 50 kGy doses for evaluation of the radiation hardness. A wide absorption band peaking at around 620 nm is observed in all as‐grown uncodoped GSAG:Ce crystals. Air annealing at high temperatures and introduction of codopants result in elimination of this absorption band and improvement of transmittance in the visible range. The nature of the color center at ≈620 nm is discussed. GSAG:Ce crystals codoped with Li+ and Mg2+:Li+ combine both high transmission and least radiation damage.
Single crystals of yttrium aluminum garnet (YAG) with Pr3+ and Ca2+ ions grown by the vertical Br... more Single crystals of yttrium aluminum garnet (YAG) with Pr3+ and Ca2+ ions grown by the vertical Bridgman method are submitted to air anneal. The influence of this process on optical absorption, photo‐, and radioluminescence is investigated in a set of samples with different concentrations of Pr and Ca. Absorption induced by the heat treatment in the 300–600 nm range in YAG:Pr,Ca is discussed, in comparison with that in YAG:Ca crystals. Photo‐ and radioluminescence spectra in as‐grown and air‐annealed samples recorded at room temperature are discussed. The features of emission decrease at 5d–4f and 4f–4f transitions of Pr3+ ions after heat treatment are considered.
Journal of Contemporary Physics (Armenian Academy of Sciences)
Abstract New expressions have been obtained to estimate the graphene thermal conductivity coeffic... more Abstract New expressions have been obtained to estimate the graphene thermal conductivity coefficient as well as characteristic dependences of coefficient of thermal conductivity on temperature and linear coefficient of thermal expansion. It has been shown that within a wide range of temperatures (about 100–700 K), the thermal conductivity values both computed and experimental ones are in good agreement.
2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2017
A large number of Yb3+-doped laser crystals are investigated as active media for ultrafast oscill... more A large number of Yb3+-doped laser crystals are investigated as active media for ultrafast oscillators and amplifiers in last decades. Yb:CALGO (Yb:CALYO) crystals demonstrate promising spectroscopic properties that confirmed by excellent experimental results in mode-locked lasers provided near-transform limited pulses with wide spectra (up to 51nm [1]). Despite this the large number of investigated femtosecond Yb-based regenerative amplifier (RA) systems were seeded by fs-pulses with narrower spectrum (≤15nm [2]) that can limit the amplified pulse bandwidth. In our paper we present for the first time to the best of our knowledge the results of experimental investigation of Yb:CALYO-based chirped pulse RA seeded by broad-band (60 nm FWHM) pulses.
2020 International Conference Laser Optics (ICLO), 2020
12W-picosecond SESAM mode-locked Yb:LuAP laser was developed. 2ps-laser pulses were obtained at t... more 12W-picosecond SESAM mode-locked Yb:LuAP laser was developed. 2ps-laser pulses were obtained at the central wavelength around 999nm and optical-to-optical efficiency of 38% at 70MHz PRF. 4.8W of second harmonic radiation was obtained using 20mm LBO crystal with critical angular phase matching. Tunability from 668nm to 783nm was obtained in preliminary experimental study of LBO based synchronously pumped OPO.
Unique spectroscopic properties of trivalent ytterbium ions in aluminium perovskite crystals (YAl... more Unique spectroscopic properties of trivalent ytterbium ions in aluminium perovskite crystals (YAlO3, LuAlO3) make these crystals good candidates for picosecond and femtosecond lasers active media. The features of soliton and non-soliton mode-locking of Yb:LuAP laser were studied. Maximum average output power of 7W with pulse duration of 130fs and 28.1 % optical efficiency were obtained in soliton mode-locking regime. Average output power up to 12W with 2ps pulse duration and 38% optical efficiency obtained in nonsoliton mode-locking regime. Chirped pulse regenerative amplifier based on Yb:LuAP crystal was investigated. Pulse duration as short as 165fs with output power of 4.5W at 200kHz pulse repetition frequency were demonstrated.
2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2019
Dual-wavelength amplifiers are in demand for a number of applications, such as laser spectroscopy... more Dual-wavelength amplifiers are in demand for a number of applications, such as laser spectroscopy, optical coherence tomography, THz generation and LIDAR instrumentation. One of the possible solution is to construct such systems based on the spectral splitting of the seed pulses generated in a laser and subsequent amplification both spectral components in an amplifier with broadband gain [1]. This leads to a significant complication of the scheme of the seed laser and amplifier.
Herein, optical‐quality single crystals of yttrium aluminum garnet (YAG):Ce,Ca,Li are grown by th... more Herein, optical‐quality single crystals of yttrium aluminum garnet (YAG):Ce,Ca,Li are grown by the vertical Bridgman method. Substitution and charge compensation mechanisms of Li+ are considered based on optical absorption in as‐grown and γ‐ray‐irradiated single crystals and their luminescence decay and rise time under X‐ray excitation. The measurements are conducted on single crystals with impurity concentrations varying over a wide range. A suitable combination of Ca and Li concentration is able to control the cerium valence, which plays a major role in the time response under ionizing radiation.
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021
Unique spectroscopic properties of Yb 3+ ions in aluminium perovskite crystals [1] , [2] (YAlO 3 ... more Unique spectroscopic properties of Yb 3+ ions in aluminium perovskite crystals [1] , [2] (YAlO 3 , LuAlO 3 ) make these crystals good candidates for picosecond and femtosecond lasers active media. Yb:LuAP crystal has wide and smooth stimulated emission (SE) cross-section spectra with values of 0.6 - 1.0x10 -20 cm 2 in the range of 1043-1016nm that is useful for femtosecond lasers. Comparatively narrow band around 999nm with FWHM spectral width of about 5nm allows sub-picosecond pulse generation and a peak SE cross-section value as high as 3.7x10 -20 cm 2 reduces critical pulse energy in mode-locking regime. Such a high SE cross-section value makes it possible efficient picosecond pulse generation even in non soliton mode-locking mode (with significantly higher threshold value). High thermooptical properties of aluminate perovskite crystals [3] , [4] together with small Stokes shift between pump and laser wavelength and utilization of quasi-off axis longitudinal pumping layout demonstrated in our previous work [5] - [8] provide high power laser action with low heat load.
Diode-pumped femtosecond chirped pulse regenerative amplifiers based on Yb3+-materials are of pra... more Diode-pumped femtosecond chirped pulse regenerative amplifiers based on Yb3+-materials are of practical importance for wide range of scientific, industrial and biomedical applications. The aim of this work was to study the amplification of broadband chirped femtosecond pulses in regenerative amplifier based on Yb3+:CaYAlO4crystal.Such systems use femtosecond mode-locked lasers as seed pulse sources and amplify nJ-seed pulses to sub-mJ energy range. Most chirped pulse regenerative amplifier systems described in the literature use seed lasers with typical pulse spectral width at the level of 10–15 nm full width at half maximum (FWHM) that limit the seed pulse duration of about 90 fs and amplified pulse duration at the level of 200 fs due to strong influence of gain narrowing effect on the amplified pulse parameters. Yb3+-doped crystals with wide and smooth gain bandwidth as an active medium of chirped femtosecond pulse regenerative amplification systems allow to reduce negative contri...
Abstract Single crystals of 151Eu:YAG were grown by the vertical Bridgman method using Eu2O3 with... more Abstract Single crystals of 151Eu:YAG were grown by the vertical Bridgman method using Eu2O3 with isotopic enrichment of 151Eu of 97.5%. Additional Hf4+or Si4+ ions were introduced to favor a high concentrations of Eu2+. As compared to Eu:YAG with natural isotope composition, the EPR spectra of YAG doped with 151Eu isotope show a reduced number of hyperfine structure components and a well-resolved structure of a bigger number of electronic transitions. Optical properties of obtained crystals and the effects of heat treatments under oxidizing and reducing conditions are reported. Based on the analysis of Eu3+ distribution in oxidized Eu,Hf:YAG, in comparison to that in Eu:YAG, the concentration of Eu2+ in as-grown Eu,Hf:YAG is determined.
The results of an experimental study of the chirped pulse amplification regime are reported for t... more The results of an experimental study of the chirped pulse amplification regime are reported for the Yb:CaYAlO<sub>4</sub> crystal with different polarization states in the gain media for the first time, to the best of our knowledge. A maximum output power of 4.2 W with 310 fs pulse duration was obtained for σ-polarization at 200 kHz repetition rate seeded by a 85 fs Yb:KYW oscillator. 215 fs pulses with an output power of 3 W and 190 fs with 2.3 W output power were demonstrated for π-polarized light in the crystal. Gain narrowing effects for different polarization states in the crystal are discussed.
Gadolinium scandium aluminum garnet scintillator crystals (GSAG:Ce) with Ca2+, Mg2+, and Li+ co‐d... more Gadolinium scandium aluminum garnet scintillator crystals (GSAG:Ce) with Ca2+, Mg2+, and Li+ co‐dopants are grown by the Bridgman method under reducing atmosphere. Crystals are irradiated with a 60Co gamma‐ray source to 10 kGy and 50 kGy doses for evaluation of the radiation hardness. A wide absorption band peaking at around 620 nm is observed in all as‐grown uncodoped GSAG:Ce crystals. Air annealing at high temperatures and introduction of codopants result in elimination of this absorption band and improvement of transmittance in the visible range. The nature of the color center at ≈620 nm is discussed. GSAG:Ce crystals codoped with Li+ and Mg2+:Li+ combine both high transmission and least radiation damage.
Single crystals of yttrium aluminum garnet (YAG) with Pr3+ and Ca2+ ions grown by the vertical Br... more Single crystals of yttrium aluminum garnet (YAG) with Pr3+ and Ca2+ ions grown by the vertical Bridgman method are submitted to air anneal. The influence of this process on optical absorption, photo‐, and radioluminescence is investigated in a set of samples with different concentrations of Pr and Ca. Absorption induced by the heat treatment in the 300–600 nm range in YAG:Pr,Ca is discussed, in comparison with that in YAG:Ca crystals. Photo‐ and radioluminescence spectra in as‐grown and air‐annealed samples recorded at room temperature are discussed. The features of emission decrease at 5d–4f and 4f–4f transitions of Pr3+ ions after heat treatment are considered.
Journal of Contemporary Physics (Armenian Academy of Sciences)
Abstract New expressions have been obtained to estimate the graphene thermal conductivity coeffic... more Abstract New expressions have been obtained to estimate the graphene thermal conductivity coefficient as well as characteristic dependences of coefficient of thermal conductivity on temperature and linear coefficient of thermal expansion. It has been shown that within a wide range of temperatures (about 100–700 K), the thermal conductivity values both computed and experimental ones are in good agreement.
2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2017
A large number of Yb3+-doped laser crystals are investigated as active media for ultrafast oscill... more A large number of Yb3+-doped laser crystals are investigated as active media for ultrafast oscillators and amplifiers in last decades. Yb:CALGO (Yb:CALYO) crystals demonstrate promising spectroscopic properties that confirmed by excellent experimental results in mode-locked lasers provided near-transform limited pulses with wide spectra (up to 51nm [1]). Despite this the large number of investigated femtosecond Yb-based regenerative amplifier (RA) systems were seeded by fs-pulses with narrower spectrum (≤15nm [2]) that can limit the amplified pulse bandwidth. In our paper we present for the first time to the best of our knowledge the results of experimental investigation of Yb:CALYO-based chirped pulse RA seeded by broad-band (60 nm FWHM) pulses.
2020 International Conference Laser Optics (ICLO), 2020
12W-picosecond SESAM mode-locked Yb:LuAP laser was developed. 2ps-laser pulses were obtained at t... more 12W-picosecond SESAM mode-locked Yb:LuAP laser was developed. 2ps-laser pulses were obtained at the central wavelength around 999nm and optical-to-optical efficiency of 38% at 70MHz PRF. 4.8W of second harmonic radiation was obtained using 20mm LBO crystal with critical angular phase matching. Tunability from 668nm to 783nm was obtained in preliminary experimental study of LBO based synchronously pumped OPO.
Unique spectroscopic properties of trivalent ytterbium ions in aluminium perovskite crystals (YAl... more Unique spectroscopic properties of trivalent ytterbium ions in aluminium perovskite crystals (YAlO3, LuAlO3) make these crystals good candidates for picosecond and femtosecond lasers active media. The features of soliton and non-soliton mode-locking of Yb:LuAP laser were studied. Maximum average output power of 7W with pulse duration of 130fs and 28.1 % optical efficiency were obtained in soliton mode-locking regime. Average output power up to 12W with 2ps pulse duration and 38% optical efficiency obtained in nonsoliton mode-locking regime. Chirped pulse regenerative amplifier based on Yb:LuAP crystal was investigated. Pulse duration as short as 165fs with output power of 4.5W at 200kHz pulse repetition frequency were demonstrated.
2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2019
Dual-wavelength amplifiers are in demand for a number of applications, such as laser spectroscopy... more Dual-wavelength amplifiers are in demand for a number of applications, such as laser spectroscopy, optical coherence tomography, THz generation and LIDAR instrumentation. One of the possible solution is to construct such systems based on the spectral splitting of the seed pulses generated in a laser and subsequent amplification both spectral components in an amplifier with broadband gain [1]. This leads to a significant complication of the scheme of the seed laser and amplifier.
Herein, optical‐quality single crystals of yttrium aluminum garnet (YAG):Ce,Ca,Li are grown by th... more Herein, optical‐quality single crystals of yttrium aluminum garnet (YAG):Ce,Ca,Li are grown by the vertical Bridgman method. Substitution and charge compensation mechanisms of Li+ are considered based on optical absorption in as‐grown and γ‐ray‐irradiated single crystals and their luminescence decay and rise time under X‐ray excitation. The measurements are conducted on single crystals with impurity concentrations varying over a wide range. A suitable combination of Ca and Li concentration is able to control the cerium valence, which plays a major role in the time response under ionizing radiation.
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021
Unique spectroscopic properties of Yb 3+ ions in aluminium perovskite crystals [1] , [2] (YAlO 3 ... more Unique spectroscopic properties of Yb 3+ ions in aluminium perovskite crystals [1] , [2] (YAlO 3 , LuAlO 3 ) make these crystals good candidates for picosecond and femtosecond lasers active media. Yb:LuAP crystal has wide and smooth stimulated emission (SE) cross-section spectra with values of 0.6 - 1.0x10 -20 cm 2 in the range of 1043-1016nm that is useful for femtosecond lasers. Comparatively narrow band around 999nm with FWHM spectral width of about 5nm allows sub-picosecond pulse generation and a peak SE cross-section value as high as 3.7x10 -20 cm 2 reduces critical pulse energy in mode-locking regime. Such a high SE cross-section value makes it possible efficient picosecond pulse generation even in non soliton mode-locking mode (with significantly higher threshold value). High thermooptical properties of aluminate perovskite crystals [3] , [4] together with small Stokes shift between pump and laser wavelength and utilization of quasi-off axis longitudinal pumping layout demonstrated in our previous work [5] - [8] provide high power laser action with low heat load.
Diode-pumped femtosecond chirped pulse regenerative amplifiers based on Yb3+-materials are of pra... more Diode-pumped femtosecond chirped pulse regenerative amplifiers based on Yb3+-materials are of practical importance for wide range of scientific, industrial and biomedical applications. The aim of this work was to study the amplification of broadband chirped femtosecond pulses in regenerative amplifier based on Yb3+:CaYAlO4crystal.Such systems use femtosecond mode-locked lasers as seed pulse sources and amplify nJ-seed pulses to sub-mJ energy range. Most chirped pulse regenerative amplifier systems described in the literature use seed lasers with typical pulse spectral width at the level of 10–15 nm full width at half maximum (FWHM) that limit the seed pulse duration of about 90 fs and amplified pulse duration at the level of 200 fs due to strong influence of gain narrowing effect on the amplified pulse parameters. Yb3+-doped crystals with wide and smooth gain bandwidth as an active medium of chirped femtosecond pulse regenerative amplification systems allow to reduce negative contri...
Abstract Single crystals of 151Eu:YAG were grown by the vertical Bridgman method using Eu2O3 with... more Abstract Single crystals of 151Eu:YAG were grown by the vertical Bridgman method using Eu2O3 with isotopic enrichment of 151Eu of 97.5%. Additional Hf4+or Si4+ ions were introduced to favor a high concentrations of Eu2+. As compared to Eu:YAG with natural isotope composition, the EPR spectra of YAG doped with 151Eu isotope show a reduced number of hyperfine structure components and a well-resolved structure of a bigger number of electronic transitions. Optical properties of obtained crystals and the effects of heat treatments under oxidizing and reducing conditions are reported. Based on the analysis of Eu3+ distribution in oxidized Eu,Hf:YAG, in comparison to that in Eu:YAG, the concentration of Eu2+ in as-grown Eu,Hf:YAG is determined.
The results of an experimental study of the chirped pulse amplification regime are reported for t... more The results of an experimental study of the chirped pulse amplification regime are reported for the Yb:CaYAlO<sub>4</sub> crystal with different polarization states in the gain media for the first time, to the best of our knowledge. A maximum output power of 4.2 W with 310 fs pulse duration was obtained for σ-polarization at 200 kHz repetition rate seeded by a 85 fs Yb:KYW oscillator. 215 fs pulses with an output power of 3 W and 190 fs with 2.3 W output power were demonstrated for π-polarized light in the crystal. Gain narrowing effects for different polarization states in the crystal are discussed.
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Papers by Karine Hovhannisyan