Evaluation of 976 nm Multimode Single Emitter Laser Diodes for Efficient Pumping of 100 W+ Yb-doped Fiber Laser

Experimental evaluation of spectral and power-current (P-I) characteristics of fiber coupled single emitter multimode laser diodes used for development of efficient pumping assembly is reported. Fiber coupled laser diodes emitting around 976 nm are best suited for pumping Yb-doped fiber lasers because of excellent coupling efficiency and reduced thermal load. We have experimentally investigated emission spectrum of fiber coupled multimode laser diodes at different temperatures and drive currents. It is found that peak emission wavelength shifts towards the longer wavelength with increase in temperature and drive current. P-I characteristics of fiber coupled laser diodes have been obtained and presented for drive current from 0.4 A to 11.5 A. Based on experiment, we have constructed spectrally matched laser diode assembly for efficient pumping of 100 W fiber laser. It requires very precise control of temperature and drive current to maintain the emission spectrum. Total 162 W power is pumped in to the Yb-doped fiber laser cavity through multi-mode pump combiners and we have obtained 110 W fiber laser output power @1070 nm. The achieved optical-to-optical efficiency is 68 per cent

Role of surface composition in morphological evolution of GaAs nano-dots with low-energy ion irradiation

The surface chemistry of GaAs (100) with 50-keV Ar(+) ion beam irradiation at off-normal incidence has been investigated in order to elucidate the surface nano-structuring mechanism(s). Core level and valence band studies of the surface composition were carried out as a function of fluences, which varied from 1 × 10(17) to 7 × 10(17) ions/cm(2). Core-level spectra of samples analyzed by X-ray photoelectron spectroscopy confirmed the Ga enrichment of the surface resulting in bigger sized nano-dots. Formation of such nano-dots is attributed to be due to the interplay between preferential sputtering and surface diffusion processes. Valence band measurement shows that the shift in the Fermi edge is higher for Ga- rich, bigger sized nano-dots due to the partial oxide formation of Ga. ‘One-dimensional power spectral density’ extracted from atomic force micrographs also confirms the significant role of surface diffusion in observed nano-structuring

Synthesis of cobalt nanoparticles on Si (100) by swift heavy ion irradiation

We report the growth and characterization of uniform-sized nanoparticles of cobalt on n-type silicon (100) substrates by swift heavy ion (SHI) irradiation. The Co thin films of 25-nm thicknesses were grown by e-beam evaporation and irradiated with two different types of ions, 45-MeV Li(3+) and 100-MeV O(7+) ions with fluences ranging from 1 × 10(11) to 1 × 10(13) ions/cm(2). SHI irradiation, with the beam rastered over the area of the film, resulted in the restructuring of the film into a dense array of Co nanostructures. Surface topography studied by atomic force microscopy revealed narrowed size distributions, with particle sizes ranging from 20 to 50 nm, formed through a self-organized process. Ion fluence-dependent changes in crystallinity of the Co nanostructures were determined by glancing angle X-ray diffraction. Rutherford backscattering spectroscopy analysis showed the absence of beam-induced mixing in this system. Surface restructuring and beam-induced crystallization are the dominant effects, with the nanoparticle size and density being dependent on the ion fluence. Results are analyzed in the context of molecular dynamics calculations of electron-lattice energy transfer

In situ electrical characteristics of 150 mev ag9+ ion beam induced damage in SI photo detector

The effect of 150 MeV Ag9+ ion irradiation on electrical characteristics of Si photo detectors has been analyzed through in-situ Current voltage (I-V) and Capacitance voltage (C-V) measurements. Ideality factor (n), series resistance (Rs) and reverse leakage current (IR) are extracted from I-V characteristics. The value of n for pristine detector is found to be 1.24 and it has increased gradually along with the fluence. The value of IR for pristine is found to be 4.97 × 10−8 A and it increases to about three orders of magnitude at the fluence of 1 × 1013 ions/cm2 and further there is no observable change. Also, C-V characteristics exhibit considerable degradation. The value of capacitance decreased from 1.13 ×10−8 F to 3.97 × 10−10 F and also carrier concentration (NA) undergoes slight decrease with the increase in fluence. The 150 MeV Ag9+ ion induced displacements, vacancies in the bulk region mainly attribute to the observed degradation in the electrical characteristics. The ionization and displacement damage profiles were estimated from SRIM/TRIM (Stopping power and Range of Ion in Matter/Transport and Range of Ion in Matter) simulation codes. The observed degradations are explained in terms of TID (total ionization dose) and Dd (displacement damage dose)