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Dive into the research topics where Ozarfar Gafarov is active.

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Featured researches published by Ozarfar Gafarov.


Optical Materials Express | 2017

Enhancement of Cr and Fe diffusion in ZnSe/S laser crystals via annealing in vapors of Zn and hot isostatic pressing

Ozarfar Gafarov; Alan Martinez; Vladimir V. Fedorov; Sergey B. Mirov

Enhancement of the thermal diffusion rates of Cr and Fe in ZnSe/ZnS was studied using two different approaches. Enhancement of Cr diffusion in ZnSe was achieved by application of excess Zn atmosphere during the thermal diffusion of Cr, where ~2.2 times improvement in the diffusion coefficient was seen over the standard diffusion technique. Also, the diffusion coefficient of Fe in ZnSe and ZnS was improved by 13 and 14 times, respectively, when diffusion was done under hot isostatic pressing.


Solid State Lasers XXVII: Technology and Devices | 2018

Grain growth and abnormal Fe diffusion in polycrystalline ZnS at elevated temperatures and pressures

Ozarfar Gafarov; Vladimir V. Fedorov; Sergey B. Mirov; Dmitriy Martyshkin

Middle-infrared (mid-IR) lasers enabling a wide range of scientific, medical, technological, and defense related applications continue to enjoy a strong demand. Transition metal (TM) doped II-VI chalcogenides are appealing mid-IR gain medial providing direct access to 1.8-6 μm spectral range. . II-VI chalcogenides are available in single crystal and in polycrystalline forms. With respect to single crystals, polycrystalline gain elements fabricated by postgrowth thermal diffusion of TM impurities in II-VI hosts feature better optical quality and enable superior laser characteristics. Despite significant progress in post-growth thermal diffusion technology, there are still some difficulties associated with the diffusion of certain TM ions in certain II-VI hosts. Specifically, the diffusion length Fe in ZnS during ~1 month annealing at 950°C is of the order of 0.1 mm. In this work, enhancement of diffusion coefficient under Hot Isostatic Pressing, at temperature and pressure of 1350°C and 2000 atm, and effect of these extreme conditions on the overall optical quality of the crystal were studied. The high temperature was applied to increase the diffusion rate, and the high pressure was needed to suppress strong sublimation and sphalerite - wurtzite phase transition at elevated temperatures. Under these conditions, the diffusion coefficient Fe in ZnS was enhanced by 5500 times as compared to standard diffusion processes carried out at 950°C. It was also demonstrated that the grain size had grown from ~30μm to ~5.5mm, which is believed to be another reason for efficient diffusion besides the elevation of temperature. The XRD patterns were measured such that the X-ray beam falls on a single grain. The XRD patterns showed only peaks characteristic to single crystals with zinc blende structure. Lasing characterization was performed to investigate the optical quality of the crystal. Slope efficiencies of 23.2% and 15.4% were obtained for TM11 and TM00 modes of operation, respectively. The emission of the laser was demonstrated to be in the 3840-3920 nm.


Laser Technology for Defense and Security XIV | 2018

Recent progress in mid-IR materials and lasers based on Cr and Fe doped chalcogenides (Conference Presentation)

Ozarfar Gafarov; Jeremy Peppers; Valentin Gapontsev; Sergey B. Mirov; Igor Moskalev; Sergey Vasilyev; Viktor O. Smolski; Mike Mirov; Vladimir Fedorov; Dmitri V. Martyshkin; Andrey Zakrevsky

II-VI chalcogenides (e.g. ZnSe/S) doped with transition metal (TM) ions such as Cr, and Fe are arguably the materials of choice for fabrication of effective mid-IR gain media. TM:II-VI materials feature a favorable blend of laser spectroscopic parameters: a four-level energy structure, absence of excited state absorption, close to 100% quantum efficiency of fluorescence (for Cr doped II-VI media), broad mid-IR vibronic absorption and emission bands. This talk summarizes progress in fabrication of high quality Cr:ZnS/Se and Fe:ZnS/Se by cation vacancy and cation interstitial enhanced post growth thermal diffusion. We also describe recent breakthrough on recrystallization and effective doping of ZnS ceramics under hot isostatic pressing resulting in a large cm-scale monocrystalline domains formation and an increase of the Fe diffusion coefficient by three orders of magnitude. We report recent advances in high-power Cr:ZnS/Se and Fe:ZnSe laser systems, enabling a wide range of tunability (1.8-5.0µm) with output power levels of up to 140 W near 2500 nm, 32 W at 2940 nm, and 35 W at 4300 nm with corresponding optical efficiencies of 62%, 29%, and 35%. Current improvements of output characteristics of polycrystalline Cr:ZnS/Se oscillators in Kerr-Lens-Mode-Locked (KLM) regime are reported: up to 2 W output power at 75-1200 MHz repetition rate, up to 2 cycle pulse duration (16 fs) with efficiency of 20-25% with regards to Er-fiber laser pump power. The effects of efficient up-conversion of mid-IR fs pulses in the laser medium as well as supercontinuum generation are demonstrated. Further extension of mid-IR spectral coverage to 3-8 m is demonstrated by Cr:ZnS KLM laser pumped degenerate (subharmonic) parametric oscillators (OPOs) based on based on quasi-phase matching in orientation-patterned gallium arsenide, and random phase matching in polycrystalline ZnSe.


conference on lasers and electro optics | 2017

Thermally-induced optical bistability in Cr and Fe doped ZnSe mid-IR laser materials

Rick Watkins; Ozarfar Gafarov; Chandler Bernard; Vladimir V. Fedorov; Sergey B. Mirov

Thermally-induced optical bistability and temperature broadening of spectroscopic bands in Cr(Fe):ZnSe mid-IR laser materials were studied over 1–6 μm spectral range to identify critical parameters for minimization of thermally induced optical noise.


Proceedings of SPIE | 2017

Temperature dependence of spectroscopic and electrical properties of Cr(Fe):ZnSe laser active materials

Ozarfar Gafarov; Rick Watkins; Chandler Bernard; Vladimir V. Fedorov; Sergey B. Mirov

Temperature influence on spectroscopic characteristics is crucial for many aspects of laser engineering including output noise, single frequency oscillation, and thermal bistability. We report on the spectroscopic characterization of chromium and iron doped ZnSe gain element media at temperatures ranging from 77K to 389K. Heating of Cr:ZnSe resulted in the absorption peak shifting to a shorter wavelength from 1.806 μm at 77K to 1.753 μm at 389K. It also resulted in broadening of the absorption band from Δλ=260 cm-1nm to Δλ=373 cm-1nm and decreasing of the absorption cross section by 69%. Similar characterization was done for Fe:ZnSe laser material. The cooling of the Fe:ZnSe crystal from room temperature to 77K resulted in a 32% increase of the absorption coefficient at 2.94 μm which is usually used as a pump source. We also studied the absorption of the electrical free-carriers in n-type Al:ZnSe crystals in visible and mid- IR absorption spectral ranges. Diffusion of Al into ZnSe samples was achieved by annealing at 1000°C during 4 days in Al vapors. It was demonstrated that free-carriers absorption of Al:ZnSe samples with resistivity σ=100-150 Ω×cm resulted in an increase of the absorption coefficient at 2.4 μm up to 2.5 cm-1.


Proceedings of SPIE | 2017

Enhancement of Fe diffusion in ZnSe/S laser crystals under hot isostatic pressing

Ozarfar Gafarov; Alan Martinez; Vladimir V. Fedorov; Sergey B. Mirov

Many organic molecules have strong and narrow absorption features in the middle Infrared (mid-IR) spectral range. The ability to directly probe absorption features of molecules enables numerous mid-IR applications in non-invasive medical diagnosis, industrial processing and process control, environmental monitoring, etc. Thus, there is a strong demand for lasers operating in mid-IR spectral range. Transition metal (TM) doped II-VI semiconductors such as Fe/Cr:ZnSe/S are the material of choice for fabrication of mid-IR gain media due to favorable combination of properties: a four level energy structure, absence of excited state absorption , broad mid-IR vibronic absorption and emission bands. Despite the significant progress in post-growth thermal diffusion technology of TM:II-VI fabrication there are still some difficulties associated with diffusion of certain TM’s in these materials. In this work we address the issue of poor diffusion of Fe in ZnSe/S polycrystals. It is well known that with the temperature increase the diffusion rate of impurity also increases. However, simple application of high temperatures during the diffusion process is problematic for ZnSe/S crystals due to their strong sublimation. The sublimation processes can be suppressed by application of high pressures. Hot isostatic pressing was utilized as the means for simultaneous application of high temperatures (1300°C) and high pressures (1000atm, 3000atm). It was determined that diffusion coefficient of Fe was improved 13 and 14 fold in ZnSe and ZnS, respectively, as compared to the standard diffusion at 950°C. The difference in diffusion coefficients can be due to strong increase in the grain size of polycrystals.


Proceedings of SPIE | 2016

Mid-IR gain media based on transition metal-doped II-VI chalcogenides

Sergey B. Mirov; Vladimir V. Fedorov; D. V. Martyshkin; Igor Moskalev; Mikhail Mirov; Ozarfar Gafarov; Alan Martinez; Jeremy Peppers; Viktor Smolski; Sergey Vasilyev; Valentin Gapontsev

Progress in fabrication and mid-IR lasing of Cr and Fe thermal-diffusion and radiation enhanced thermal diffusion doped II-VI binary and ternary polycrystals is reported. We demonstrate novel design of mid-IR Fe:ZnSe and Cr:ZnSe/S solid state lasers with significant improvement of output average power up to [email protected] μm and [email protected] μm and [email protected] μm. We report significantly improved output characteristics of polycrystalline Cr:ZnS/Se lasers in gain-switched regime: 16 mJ at 200 Hz, pulse duration 5 ns with tunability over 2400-3000 nm as well as Kerr-Lens-Mode-Locked regime in terms of average power (up to 2 W), peak power and pulse energy (0.5 MW and 24 nJ, respectively), and pulse duration (less than 29 fs).


Lasers Congress 2016 (ASSL, LSC, LAC) (2016), paper AM5A.12 | 2016

Enhancement of Cr and Fe Diffusion in ZnSe/S Laser Crystals via Annealing in Vapors of Zn and Hot Isostatic Pressing

Ozarfar Gafarov; Vladimir V. Fedorov; Sergey B. Mirov

Chromium and Iron ions diffusion in Zn vapors and under high Argon pressure are studied. The diffusion coefficient of Fe in ZnS was improved by 60 times under hot isostatic pressing at 3000 atm.


Proceedings of SPIE | 2015

Radiation-Enhanced Thermal Diffusion of Transition Metal and Rare Earth Ions into II-VI Semiconductors

Alan Martinez; Lamario Williams; Ozarfar Gafarov; D. V. Martyshkin; Vladimir V. Fedorov; Sergey B. Mirov

We report on study of gamma radiation-enhanced thermal diffusion of Transition Metal and Rare Earth ions into IIVI semiconductor crystals. ZnSe and ZnS samples with of iron thin film deposited on one facet were sealed in evacuated quartz ampoules at 10-3 Torr. The crystals were annealed for 14 days at 950°C under γ-irradiation from 60Co source. The irradiation dose rates of 43.99 R/s, 1.81 R/s were varied by distance between 60Co source and furnaces. For comparison, the samples were also annealed without irradiation at the same temperature. The spatial distributions of transition metal were measured by absorption of focused laser radiation at 5T2-5E mid-IR transitions of iron ions. In addition, samples of ZnSe were similarly sealed in evacuated quartz ampoules in the presence of Praseodymium metal and annealed at 950°C under 43.99 R/s and 0 R/s and the diffusion lengths and Pr concentrations were compared. The γ-irradiation results in better intrusion of the iron ions from the metal film and increase of the diffusion length at ~25%, while Praseodymium diffusion is dramatically enhanced by γ-irradiation during the annealing process.


conference on lasers and electro optics | 2015

Spectroscopic characterization of Pr 3+ :ZnSe crystals fabricated via post-growth thermal diffusion

Alan Martinez; Ozarfar Gafarov; D. V. Martyshkin; Vladimir V. Fedorov; Sergey B. Mirov

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Sergey B. Mirov

University of Alabama at Birmingham

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Vladimir V. Fedorov

University of Alabama at Birmingham

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Alan Martinez

University of Alabama at Birmingham

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D. V. Martyshkin

University of Alabama at Birmingham

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Rick Watkins

University of Alabama at Birmingham

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Chandler Bernard

University of Alabama at Birmingham

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Jeremy Peppers

University of Alabama at Birmingham

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Vladimir Fedorov

Russian Academy of Sciences

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Dmitri V. Martyshkin

University of Alabama at Birmingham

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Lamario Williams

University of Alabama at Birmingham

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