We have demonstrated a Yb:Ta2O5 waveguide laser fabricated by RF magnetron sputtering on oxidised silicon. The waveguide laser was end-pumped with a laser diode at 977 nm and lasing was observed between 1015 and 1020 nm. The launched pump power threshold and slope efficiency were measured to be ~25 mW and 1.78 %, respectively

Baum, S.

Kharb, Preeti

Lister, Matthew L.

Marshall, Herman

O'Dea, Christopher P.

Stanley, E. C.

The Astrophysical Journal

English

arXiv

E. C. Stanley

P. Kharb

M. L. Lister

H. L. Marshall

C. O’Dea

S. Baum

Crossref

A MULTIWAVELENGTH STUDY OF THREE HYBRID BLAZARS

We present multiwavelength imaging observations of PKS 1045−188, 8C 1849+670, and PKS 2216−038, three radio-loud active galactic nuclei from the MOJAVE-Chandra Sample that straddle the Fanaroff-Riley (FR) boundary between low- and high-power jets. These hybrid sources provide an excellent opportunity to study jet emission mechanisms and the influence of the external environment. We used archival VLA observations, and new Hubble and Chandra observations to identify and study the spectral properties of five knots in PKS 1045−188, two knots in 8C 1849+670, and three knots in PKS 2216−038. For the seven X-ray visible knots, we constructed and fit the broadband spectra using synchrotron and inverse Compton/cosmic microwave background (IC/CMB) emission models. In all cases, we found that the lack of detected optical emission ruled out the X-ray emission from the same electron population that produces radio emission. All three sources have high total extended radio power, similar to that of FR II sources. We find this is in good agreement with previously studied hybrid sources, where high-power hybrid sources emit X-rays via IC/CMB and the low-power hybrid sources emit X-rays via synchrotron emission. This supports the idea that it is total radio power rather than FR morphology that determines the X-ray emission mechanism. We found no significant asymmetries in the diffuse X-ray emission surrounding the host galaxies. Sources PKS 1045−188 and 8C 1849+670 show significant differences in their radio and X-ray termination points, which may result from the deceleration of highly relativistic bulk motion

DSpace@MIT

A MULITWAVELENGTH STUDY OF THREE HYBRID BLAZARS

Aghajani, A.

Murugan, G.S.

Sessions, N.P.

Apostolopoulos, V.

Wilkinson, James S.

Southampton (e-Prints Soton)

     Ytterbium-Doped Tantalum Pentoxide Waveguide Lasers A. Aghajani 1, G.S. Murugan1, N.P. Sessions1, V. Apostolopoulos2, J. S. Wilkinson1 1 Optoelectronics Research Centre, University of Southampton, Southampton, England aa15v07@soton.ac.uk, smg@orc.soton.ac.uk, nps@orc.soton.ac.uk, jsw@orc.soton.ac.uk    2 School of Physics and Astronomy, University of Southampton, Southampton, England v.apostolopoulos@soton.ac.uk Abstract:  We  have  demonstrated  a  Yb:Ta2O5  waveguide  laser  fabricated  by  RF  magnetron sputtering on oxidised silicon. The waveguide laser was end-pumped with a laser diode at 977 nm and lasing was observed between 1015 and 1020 nm. The launched pump power threshold and slope efficiency were measured to be ~25 mW and 1.78 %, respectively.   Introduction Integrated channel waveguide solid-state lasers are key components in the quest for fully integrated optical circuits with advanced functionality such as tunability and pulsed operation. Ta2O5 has been selected as the host material for the realization of a compact, integrated ytterbium doped waveguide laser  as  it  offers  many  important  attributes  such  as  good  ability  to  host  rare-earth  ions,  as demonstrated with erbium1 and neodymium2, a large third nonlinearity3 and a high refractive index (n ≈ 2.124 at λ ≈ 980 nm)4, and is suitable for mode-locking. High index contrast between the waveguide core and cladding provides for low-loss tight bend radii enabling the development of compact and ultra-small photonic circuits due to the strong confinement of the optical modes. In this work, we present for the first time lasing behaviour for Yb:Ta2O5 rib waveguides and quantify the absorption and emission cross-sections of the material and the threshold, slope efficiency and emission spectrum of waveguide laser.  Device design and fabrication Rib waveguides in Ta2O5 were designed for single mode (SM) operation between 970 nm and 1100 nm, covering the signal and pump wavelengths of Yb-doped materials. Rib waveguide dimensions of 1 µm rib height and 150 nm etch depth were selected using Soref et al.5 method. A Yb:Ta2O5 film of 1 μm was deposited by RF magnetron sputtering from a power-pressed tantalum pentoxide  target,  doped  with  2.5  wt%  of  ytterbium  oxide  (~6.2x1020  atoms/cm3)  onto  a  silicon substrate coated with a 2.5 μm thermally-grown silica layer. The conditions used for the deposition process were 20 and 5 sccm of argon and oxygen gas flow, a substrate temperature of 200oC and magnetron power of 300 W. These conditions were previously optimized for Er:Ta2O5 to provide the lowest optical loss with an acceptable deposition rate6. The  rib  waveguides  were  structured  by  conventional photolithography  and  argon  ion  beam  milling  (IBM). Channel waveguides were fabricated with an etch depth of 150 nm and with widths ranging from 1 to 10 μm. Once the structuring process was complete, a 1.6 μm thick silica overcladding  was deposited on top of the waveguide  core,  producing  a  protection  layer  and  a symmetrical  waveguide.  For  preparation  for  optical measurements the wafer was cut into smaller samples and end facets were polished to optical quality.    Waveguide and lasing characteristics The spectral characteristics of Yb:Ta2O5 were unknown so an absorption spectrum was obtained to determine the ytterbium cross section at the pump (977 nm) wavelength. Broadband (700 – 1700nm) light from a tungsten halogen lamp was coupled into a 3 mm long waveguide using a monomode fibre and  collected  at the  output  using  a  multimode  fiber.  The collected light  was fed  into  an optical spectrum analyzer (OSA). Fig 1 shows the absorption cross section of Yb:Ta2O5, using the estimated Fig 1: Absorption cross-section 0.00.51.01.52.02.53.0850 900 950 1000 1050 1100Absorption cross section (cm2 X10-20)Wavelength (nm)     concentration of ytterbium ions in Ta2O5 (6.2x1020 atoms/cm3). The absorption bands of ytterbium at 935 nm and 975 nm are clearly visible with a peak absorption cross section (σabs) of 2.75 ± 0.17 x10-20 cm2 evident in the pump band at 975 nm. The peak emission cross section (σem) was also estimated using the reciprocity method from the absorption cross section, giving a peak emission cross section of 2.9 ± 0.7x10-20 cm2 at 975 nm. A 10.8 mm long laser cavity was formed using the reflections from the parallel optically polished end facets  alone,  which  were  estimated  to  have  a  Fresnel  reflectivity  of  12  %  at  the  waveguide-air interface. To  demonstrate lasing,  the  pump  was  butt-coupled  into  the end  facet  of a  3  μm  wide waveguide using a monomode fibre, exciting the fundamental mode. Light emerging from the output was collected using a ×40 objective lens and passed through a set of long pass filters with a cut-off wavelength of 1 μm to remove the residual pump radiation. The wavelengths at which lasing occurred ranged from 1015 nm  to 1020 nm as shown in Fig. 2b. The lasing output power is plotted against the launched  pump  power,  Fig.  2a,  and  the  laser  threshold  and  single-ended  slope  efficiency  were determined to be ~25 mW and 1.78 %, respectively.  0.000.050.100.150.200.250 10 20 30 40Output power (mW)Launch Power (mW)-60-50-40-30-20-100990 1010 1030 1050Optical intensity (dBm/nm)Wavelength (nm)  Fig 2: a) Laser output power versus launched pump power b) Lasing spectrum of Yb:Ta2O5 Conclusion In  conclusion,  we  have  demonstrated  a Yb:Ta2O5  waveguide  laser  fabricated  by  RF magnetron sputtering on a silicon wafer, and determined  spectroscopic  parameters  and lasing  characteristics.  The  waveguide  laser was end pumped with a laser diode at 977 nm and  lasing  was  observed  between  1015  and 1020  nm  using  only  the  polished  facets  as mirrors. The launched pump power threshold and slope efficiency were measured to be ~25 mW and 1.78 %, respectively. This material system has demonstrated that compact continuous wave lasing  is  achievable,  providing  a  platform  to  develop  monolithically  integrated  components  and devices. Improvements in lasing characteristic can be realised through optimisation of cavity mirrors, or with ring resonators exploiting the high index contrast. The gain properties and nonlinearity of the material, and their fabrication with CMOS-compatible processes, offers a potential route to low-cost mass production of highly functional integrated mode-locked and tunable lasers. References 1. A. Z. Subramanian, C. J. Oton, D. P. Shepherd J. S. Wilkinson, Photon. Technol. Lett,. 22, pp. 1571-1573, (2010). 2. B. Unal et al., J. Quantum Electron., 41, pp. 1565-1573, (2005) 3. C. Y. Tai et al., Optics Express, 21, pp 5110 - 5116 (2004) 4. A. Z. Subramanian, Tantalum Pentoxide Waveguide Amplifier and Laser for Planar Lightwave Circuits, University of Southampton thesis (2011) 5. R. Soref, J. Schmidtchen, K. Petermann, J. Quantum Electron., 27, pp. 1971-1974, (1991) 6. A.Z. Subramanian, G.S. Murugan, M.N. Zervas, J.S. Wilkinson, J. Lightwave Technol.,  30, pp. 1455-1462 (2012). Symbols  Definition  Values No  Yb dopant concentration  6.2x1020 cm-3 σabs  Peak absorption cross section 2.75x10-20 cm2 σem  Peak emission cross section 2.9x10-20 cm2 λp  Pump wavelength  977 nm λs  Signal wavelength  1015-1020 nm a)  b) Table 1: Spectroscopic parameters for Yb:Ta2O5 

75x10 -20 cm σem Peak emission cross section

9x10 -20 cm λp Pump wavelength 977 nm λs Signal wavelength 1015-1020 nm a) b) Table 1: Spectroscopic parameters for Yb:Ta2O5

Symbols Definition Values No Yb dopant concentration 6.2x10 20 cm -3 σabs Peak absorption cross section

Tantalum Pentoxide Waveguide Amplifier and Laser for Planar Lightwave Circuits, University of Southampton thesis