Dmitri V. Martyshkin

Recent Progress in Transition-Metal-Doped II–VI Mid-IR Lasers

Recent progress in transition metal (TM)-doped II-VI semiconductor materials (mainly Cr2+:ZnSe) makes them the sources of choice for laser when one needs a compact continuous wave (CW) system with tunability over 1.9-3.1 mum, output powers up to 2.7 W, and high (up to 70%) conversion efficiency. The unique combination of technological (low-cost ceramic material) and spectroscopic characteristics make these materials ideal candidates for new regimes of operation such as microchip and multiline lasing. This paper reviews these nontraditional Cr-doped middle-infrared (mid-IR) lasers as well as describes emerging Fe2+:ZnSe lasers having potential to operate at room temperature (RT) over the spectral range extended to 3.7-5.1 mum. In addition to being wideband semiconductors, effective RT mid-IR lasing TM-doped II-VI media also hold potential for direct electrical excitation. This paper shows the initial steps toward achieving this goal by studying Cr2+-Co2+- and-doped quantum dots. We have demonstrated a novel method of TM-doped II-VI quantum dots fabrication based on laser ablation in liquid environment. TM-doped II-VI quantum dots demonstrated strong mid-IR luminescence. It opens a new pathway for future optically and electrically pumped mid-IR lasers based on TM-doped quantum confined structures.

Effective suppression of fluorescence light in Raman measurements using ultrafast time gated charge coupled device camera

A high level of fluorescence background signal rejection was achieved for solid and powder samples by using a combination of simple low-resolution spectrograph and ultrafast gated charge coupled device (CCD) camera. The unique timing characteristics of the CCD camera match exceptionally well to characteristics of a Ti:sapphire oscillator allowing fast gated light detection at a repetition rate of up to 110 MHz, making this approach superior in terms of the duty cycle in comparison with other time-resolved Raman techniques. The achieved temporal resolution was about 150 ps under 785 nm Ti: sapphire laser excitation. At an average excitation power up to 300 mW there was no noticeable sample damage observed. Hence, the demonstrated approach extends the capabilities of Raman spectroscopy regarding the investigation of samples with a short fluorescence lifetime. The combination of a spectrometer and a gated CCD camera allows simultaneous study of spectral and temporal characteristics of emitted light. This cap...

Energy scaling of 4.3 μm room temperature Fe:ZnSe laser

We demonstrate a fourfold increase of the output energy of the gain-switched mid-IR Fe:ZnSe laser. Iron doping of the ZnSe polycrystalline samples was realized using a postgrowth thermal-diffusion method from the metal film. Gain-switched Er:Cr:YSGG (2.8 μm) laser pumped Fe:ZnSe lasing was studied in a Fabry-Perot cavity over a 236-300 K temperature range. The maximum output energy reached 4.7 mJ at 4.3 μm and 3.6 mJ at 4.37 μm at 236 K and 300 K and was limited only by available pump energy. The laser threshold was about 8 mJ and was practically unchanged over the studied temperature range. The laser slope efficiencies, measured with respect to the input pump energy, decreased from 19% to 16% with an increase of temperature from 236 to 300 K. The output radiation featured a Gaussian spatial profile with M(2) = 2.6.

Hemoglobin adsorption isotherm at the silica-water interface with evanescent wave cavity ring-down spectroscopy

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) is used to observe the adsorption isotherm for hemoglobin (Hb) from controlled urine samples to assess the potential for rapid diagnosis in hemoglobinuria. The absorbance of Hb at 425 nm is monitored using an alexandrite laser-pumped, room temperature, LiF:F2+** color-center pulsed laser. A minimum absorbance detection level of 2.57 x 10(-4) is achieved, corresponding to a minimum detectable concentration of Hb in urea of 5.8 nM. A multilayered Hb biofilm is formed, and a minimum of eight layers are required to model the adsorption isotherm, allowing for cooperative binding within the layers and extending 56 nm into the interface. A binding constant for Hb to silica 18.23+/-7.58 x 10(6) M is derived, and a binding constant for Hb to Hb in subsequent layers is determined to be 5.631+/-0.432 x 10(5) M. Stoichiometric binding coefficients of 1.530+/-0.981 for layer one and 1.792+/-0.162 for subsequent layers suggest that cooperative binding both to the silica surface and between the layers of the biofilm is important.

Energy scaling of room temperature Fe2+:ZnSe gain-switched 4.3 μm laser

We report an optimization of Fe:ZnSe crystals fabrication, as well as a fourfold increase of the output energy of the gain-switched middle-infrared Fe:ZnSe laser pumped by the radiation of Q-switched Cr:Er:YSGG (2.8μm) laser. Lasing was studied over 236-300K temperature range. In Fabry-Perot cavity with 18% OC reflectivity the maximum output energy reached 4.7 mJ @ 4.3μm and 3.6 mJ @ 4.37μm at 236K and 300K, respectively and was limited only by available pump energy. Threshold was about 8 mJ and was practically unchanged over studied temperature range. The laser slope efficiencies decreased from 19% to 16 % with an increase of temperature from 236 to 300K.

Cr-ZnSe passively Q-switched fiber-bulk Ho:YAG hybrid laser

The objective of this work was to develop a compact and efficient Tm-fiber-Ho:YAG, hybrid laser passively Q-switched by Cr:ZnSe saturable absorber. We used a folded semi-hemispherical 10 cm long cavity with a plane output coupler and a 0.5 m concave high reflector. In these experiments we studied the performance of two high optical quality Cr:ZnSe crystals as saturable absorbers with initial transmissions of 93.9% and 70% at 2.1 μm. With the 93.9% transmission crystal, passive Q-switching was realized with a maximum output power of 5 W, pulse energy of 0.5 mJ, pulse duration of 150 ns, and Q-switched-to-CW-mode extraction efficiency of 60%. With the 70% transmission crystal, passive Qswitching was achieved with a 75% Q-switched-to-CW-mode extraction efficiency, pulse energy of 3 mJ, and duration of 7ns. The laser demonstrated sustained damage-free, TEM000 operation with 0.5 MW of peak power showing promise for applications requiring high-peak-power, diffraction-limited beams, and single-frequency regimes of operation.

Fluorescence assay for monitoring Zn-deficient superoxide dismutase in vitro.

A method has been developed for selective detection of the zinc-deficient form of Cu, Zn superoxide dismutase (SOD1) in vitro. Zinc-deficient SOD1 mutants have been implicated in the death of motor neurons leading in amyotrophic lateral sclerosis (ALS or Lou Gerhigs disease). Thus, this method may have applicability for detecting zinc-deficient SOD1 mutants in human ALS patients samples as well as in a transgenic mouse model of ALS and in cultured motor neurons. We determined previously that structural analogs of 1,10 phenanthroline, which react specifically with Cu(I), react with the active Cu(I) of SOD1 when zinc is absent, but not when zinc is also bound, as evidenced by the fact that the reaction is inhibited by pretreatment of the enzyme with zinc. We report herein that bathocuproine, or its water-soluble derivative bathocuproine disulfonate, react with zinc-deficient SOD1 to form a complex which fluoresces at 734 nm when excited at 482 nm. Fluorescent intensity is concentration dependent, thus we propose to use fluorescent confocal microscopy to measure intracellular levels of zinc-deficient SOD1 in situ.

Laser damage resistant anti-reflection microstructures for mid-infrared metal-ion doped ZnSe gain media

Power scaling of mid-infrared laser systems based on chromium and iron doped zinc selenide (ZnSe) and zinc sulfide (ZnS) crystals is being advanced through the integration of surface relief anti-reflection microstructures (ARMs) etched directly in the facets of the laser gain media. In this study, a new ARMs texture fabrication process is demonstrated for polycrystalline ZnSe and ZnS material that results in a significant increase in pulsed laser damage resistance combined with an average reflection loss of less than 0.5% over the wavelength range of 1.9-3.0μm. The process was utilized to fabricate ARMs in chromium-doped zinc selenide (Cr2+:ZnSe) materials supplied by IPG Photonics and standardized pulsed laser induced damage threshold (LiDT) measurements at a wavelength of 2.09μm were made using the commercial testing services of Spica Technologies. It was found that the pulsed LiDT of ARMs etched in ZnSe and Cr2+:ZnSe can match or even exceed the level of a well-polished surface, a survivability that is many times higher than an equivalent performance broad-band thin-film AR coating. The results also indicate that the ARMs plasma etch process may find use as a post-polish damage mitigation technique similar to the chemical immersion used to double the damage resistance of fused silica optics. ARMs etched in Cr2+:ZnSe were also evaluated by IPG Photonics for survivability under continuous wave (CW) laser operation at a pump laser wavelength of 1.94μm. Catastrophic damage occurred between power levels of 400-500 kilowatt per square centimeter for both as polished and ARMs textured samples indicating no reduction in CW damage resistance attributable to surface effects.

Novel laser breakdown spectrometer for environmental monitoring

A novel experimental set-up using laser-induced breakdown spectroscopy (LIBS) for environmental analyses of heavy metals is described in this paper. It is based on state-of-the-art spectroscopic equipment, advanced detectors, and laser atomizers: a 0.75 m spectrometer ARC-750, intensified TE- cooled 256 X 1024 CCD camera, probe with fiber optic guide for signal transportation, and Nd:YAG laser plasma atomizers with two different methods for sample delivery. In the first method the liquid solution containing the atoms to be investigated is drawn into the chamber of the nebulizer. The mixture passes through the nozzle, accompanied by argon gas along with formed aerosol, and enters the plasma plume, which is generated by the laser spark in argon. The second method is based on direct generating of the plasma in the water jet of a continuously circulating sample. LIBS testing of samples containing Al, Cd, Cu, Fe, Pb, Zn, and Cr ions was compared with results using atomic absorption spectrophotometry. Initial indications showed good agreement between these two methods. Detection levels of less than 100 ppb were observed for copper and chromium. The described spectroscopic system exhibits high sensitivity, accumulation of luminescence spectrum in real time; and high dynamic range for concentrations detection from 100 ppb to 1000 ppm.

Mid-IR luminescence of nanocrystalline II-VI semiconductors doped with transition metal ions

A novel method of transition metal (TM) (Cr, Co and Fe) doped II-VI nanocrystalline quantum dots (NCD) fabrication based on laser ablation was demonstrated. For the first time mid-IR luminescence from TM:II-VI NCD is reported.