D. V. Martyshkin

Progress in Mid-IR Lasers Based on Cr and Fe-Doped II–VI Chalcogenides

Transition metal (TM) doped II-VI chalcogenide laser materials offer a unique blend of physical, spectroscopic, and technological parameters that make them the gain media of choice for cost effective broadly tunable lasing in the Mid-IR. The II-VI semiconductor hosts provide a low phonon cut-off, broad IR transparency, and high thermal conductivity. When doped with transition metal ions, these materials feature ultrabroadband gain, low saturation intensities, and large pump absorption coefficients. This combined with the low-cost mass production technology of crystal fabrication by postgrowth thermal diffusion, as well as broad availability of convenient pump sources, make these materials ideal candidates for broadly tunable mid-IR lasing in CW, gain-switched, free running, and mode-locked regimes of operation. This review summarizes experimental results on optically pumped lasers based on Cr and Fe doped II-VI wide band semiconductors providing access to the 1.9-6 μm spectral range with a high (exceeding 60%) efficiency, multi-Watt-level (18 W in gain switch and 30 W in pure CW) output powers, tunability in excess of 1000 nm, short-pulse (<;50 fs) multi-watt oscillation, multi-Joule long-pulse output energy, and narrow spectral linewidth (<;100 kHz).

Progress in mid-IR Cr 2+ and Fe 2+ doped II-VI materials and lasers [Invited]

Recent progress in fabrication and mid-IR lasing of transition metal doped II-VI single crystal and thermo-diffusion doped polycrystalline and hot-pressed ceramic gain media as well as nano and micro-crystalline laser active powders, powders in the liquid suspension, polymer-film, thin film waveguides and chalcogenides glass composites is reported.

Mid-IR laser oscillation in Cr 2+ :ZnSe planar waveguide

We demonstrate 2.6 µm mid-infrared lasing at room temperature in a planar waveguide structure. Planar waveguides were fabricated using pulsed laser deposition (PLD) by depositing chromium doped zinc selenide thin films on sapphire substrate (Cr2+:ZnSe/sapphire). Highly doped Cr2+:ZnSe/Sapphire thin film sample was also used to demonstrate passive Q-switching of Er:YAG laser operating at 1.645 µm.

Mid-IR random lasing of Cr-doped ZnS nanocrystals

The laser ablation method enabled fabrication of transition-metal (Cr, Co, Fe)-doped nanocrystals with a strong photoluminescence over a 2?5? ?m spectral range. The first room temperature mid-IR random lasing due to impurity intra-shell transitions in transition-metaldoped semiconductor nanocrystals is reported. Temperature dependences of the lasing spectra reveal diverse behaviour of the output spectra for powders of different grain sizes.

Mid-infrared Cr 2+ :ZnSe random powder lasers

We report simple methods of laser active Cr2+:ZnSe powder fabrication with average grain sizes of either approximately 10 or approximately 1 microm without crystal growth stage. Pure, uniformly mixed ZnSe and CrSe powders annealed at 1000 masculineC for 3 days in a sealed evacuated (approximately 10(-4) Torr) quartz ampoule exhibited middle-infrared laser action at room temperature under 1.56 microm excitation of D(2) Raman shifted radiation of Nd:YAG laser. The output-input characteristic clearly demonstrated the threshold-like behavior of the output signal with the threshold energy level of 0.5 and 3 mJ in 2.9 mm spot for 10 and 1 microm grain sizes, respectively.

Crystalline Cr 2+ :ZnSe/chalcogenide glass composites as active mid-IR materials

We propose new transition metal (TM)-doped ZnSe/As₂S₃:As₂Se₃ composite materials for mid-IR fiber lasers. The composites are the suspension of crystalline micro- and nanosized TM²⁺:ZnSe or TM²⁺:ZnS powders in chalcogenide glasses with the refraction index matching. Mid-IR room-temperature lasing of Cr²⁺:ZnSe/As₂S₃:As₂Se₃ microcomposite material is demonstrated at the 2.4 μm wavelength.

Gold Nanorod Bioconjugates for Active Tumor Targeting and Photothermal Therapy

The mastery of active tumor targeting is a great challenge in near infrared photothermal therapy (NIRPTT). To improve efficiency for targeted treatment of malignant tumors, we modify the technique of conjugating gold nanoparticles to tumor-specific antibodies. Polyethylene glycol-coated (PEGylated) gold nanorods (GNRs) were fabricated and conjugated to an anti-EGFR antibody. We characterized the conjugation efficiency of the GNRs by comparing the efficiency of antibody binding and the photothermal effect of the GNRs before and after conjugation. We demonstrate that the binding efficiency of the antibodies conjugated to the PEGylated GNRs is comparable to the binding efficiency of the unmodified antibodies and 33.9% greater than PEGylated antibody-GNR conjugates as reported by Liao and Hafner (2005). In addition, cell death by NIRPTT was sufficient to kill nearly 90% of tumor cells, which is comparable to NIRPTT with GNRs alone confirming that NIRPTT using GNRs is not compromised by conjugation of GNRs to antibodies.

A histological evaluation and in vivo assessment of intratumoral near infrared photothermal nanotherapy-induced tumor regression

Purpose Nanoparticle (NP)-enabled near infrared (NIR) photothermal therapy has realized limited success in in vivo studies as a potential localized cancer therapy. This is primarily due to a lack of successful methods that can prevent NP uptake by the reticuloendothelial system, especially the liver and kidney, and deliver sufficient quantities of intravenously injected NPs to the tumor site. Histological evaluation of photothermal therapy-induced tumor regression is also neglected in the current literature. This report demonstrates and histologically evaluates the in vivo potential of NIR photothermal therapy by circumventing the challenges of intravenous NP delivery and tumor targeting found in other photothermal therapy studies. Methods Subcutaneous Cal 27 squamous cell carcinoma xenografts received photothermal nanotherapy treatments, radial injections of polyethylene glycol (PEG)-ylated gold nanorods and one NIR 785 nm laser irradiation for 10 minutes at 9.5 W/cm2. Tumor response was measured for 10–15 days, gross changes in tumor size were evaluated, and the remaining tumors or scar tissues were excised and histologically analyzed. Results The single treatment of intratumoral nanorod injections followed by a 10 minute NIR laser treatment also known as photothermal nanotherapy, resulted in ~100% tumor regression in ~90% of treated tumors, which was statistically significant in a comparison to the average of all three control groups over time (P<0.01). Conclusion Photothermal nanotherapy, or intratumoral nanorod injections followed by NIR laser irradiation of tumors and tumor margins, demonstrate the potential of NIR photothermal therapy as a viable localized treatment approach for primary and early stage tumors, and prevents NP uptake by the reticuloendothelial system.

High Average Power Fe:ZnSe and Cr:ZnSe Mid-IR Solid State Lasers

We report on novel design of tunable mid-IR Fe:ZnSe and Cr:ZnSe solid state lasers which provided significant increase of output average power up to 35W@4.1 µm and 57W@2.5 µm and 20W@2.94 µm.

A fiber pumped Er:YAG laser passively Q-switched by Co:ZnS and Cr:ZnSe crystals

Passive Q-switching of an Er-fiber–Er:YAG hybrid laser was realized by Co:ZnS and Cr:ZnSe saturable absorbers enabling operation on the 1645 nm and 1617 nm lasing transitions respectively. Single- and multi-mode regimes of operation were analyzed experimentally and theoretically.