9,144 research outputs found
Comparative molecular genetics of the German Shepherd dog
No full textIncludes bibliographical references (leaves 105-111).Microsatellite markers were used to measure genetic diversity and population differentiation within and between domestic dog breeds. The German Shepherd Dog was compared with typical outbred mongrel dogs, Dachshunds, Staffordshire Bull Terriers and a cohort of other pedigreed dogs representing 30 recognised breeds. Although archaeological records report that grey wolves (Canis lupus) were domesticated approximately 14 000 years ago, mtDNA analysis suggests that domestic dogs (Canis familiaris) and grey wolves diverged in multiple events over 100 000 years ago. Subsequently, the movement of humans and their dogs resulted in extensive gene flow between dog populations for thousands of years. Breeding practices to obtain distinctive pnenotypic uniformity were recently introduced, resulting in pure-bred dogs becoming essentially closed gene pools. However, further mtDNA analyses have reported unexpectedly high levels of variability, supported by microsatellite loci with heterogeneities of between 36% and 55% being reported for some dog breeds. Microsatellite analyses of 15 polymorphic canine loci are reported. German Shepherd Dogs and outbred mongrel dogs expressed diversity values of 4.0 alleles per locus in the former and 6.4 in the later (corrected for population size by jack-knifing with 1 000 pseudoreplications), with expected heterozygosities of 62% and 83%, respectively. German Shepherd Dogs showed a moderate loss of genetic diversity relative to outbred dogs, but not sufficient to describe the breed as highly inbred. However, in comparison with other pure-bred dogs examined, they expressed the least genetic diversity, with Dachshunds having 5.2, Staffordshire Bull Terriers 4.8 and the composite group of pedigreed dogs 6.0 alleles per locus, with expected heterozygosities of 72%, 67% and 80%, respectively. Significant population differentiation (GST = 0.103; RST = 0.058) between German Shepherd Dogs and the outbred dogs illustrates the effect of genetic drift since the breed was established just over 100 years ago. This study would benefit future breeding programs, as management should be facilitated by knowledge of relative measures of inbreeding and differentiation, especially between various separate breeding stocks within the breed
Diffraction grating tuning of a high power synchronously pumped PPLN OPO
No full textA diffraction grating is used for tuning a synchronously pumped periodically poled lithium niobate optical parametric oscillator, and its high-output-power performance investigated. Higher order signal modes, caused by pulse-front-tilt, are observed, but are readily suppressed
Synchronously pumped CdSe optical parametric oscillator in the 9-10µm region
No full textContinuous mode-locked operation of a singly resonant, synchronously pumped optical parametric oscillator (SPOPO) based on CdSe has produced idler output tuned over the range of 9.19.7 µm , the longest wavelength generated so far to our knowledge from a SPOPO. Average idler powers as high as 70 mW are generated in the crystal. Tandem pumping with a diffraction-grating-tuned parametric oscillator in periodically poled lithium niobate provides a convenient and agile means of tuning the noncritically phase-matched CdSe device. The absence of any detrimental thermal effects in the CdSe crystal suggests that significant further power scaling should be possible, with idler tuning ranges extendable to cover 812 µm
Efficient blue upconversion emission due to confined radiative energy transfer in Tm<sup>3+</sup>:Nd<sup>3+</sup> co-doped Ta<sub>2</sub>O<sub>5</sub> waveguides under infrared-laser excitation
No full textIntense blue upconversion emission at 480nm has been obtained at room temperature in Tm3+:Nd3+ co-doped Ta2O5 channel waveguides fabricated on a Si substrate, when the sample is excited with an infrared laser at 793nm. The upconversion mechanism is based on the radiative relaxation of the Nd3+ ions (4F3/2 to 4I11/2) at about 1064nm followed by the absorption of the emitted photons by Tm3+ ions in the 3H4 excited state. A coefficient of energy transfer rate as high as 3 × 10-16 cm3/s has been deduced using a rate equation analysis, which is the highest reported for Tm-Nd co-doped systems. The confinement of the 1064nm emitted radiation in the waveguide structure is the main reason of the high energy transfer probability between Nd3+ and Tm3+ ions
Synchronously pumped optical parametric oscillator with diffraction-grating tuning
No full textThe operating characteristics of a synchronously pumped optical parametric oscillator, based on periodically poled lithium niobate (PPLN), with a diffraction grating as the tuning element, are described and compared with design expectations. Operation at average signal output power levels of up to 2.0 W has been achieved and signal/idler tuning in the range 1.466-3.663 µm has been investigated using the tilt of the diffraction grating, while keeping the temperature of the PPLN fixed. A detailed investigation has been made of the operating characteristics that might be influenced by the presence of pulse tilt caused by the grating. It is shown that any adverse effects of tilt on beam quality can be small, with the main observed effect being an excess loss. An observed tendency to oscillate in higher-order transverse modes on the long-wavelength side of the tuning range is ascribed to non-collinear phase-matching. This higher-order-mode oscillation is easily prevented by the insertion of an aperture. The analysis presented here includes a grating loss calculation and the calculation of the tuning range achievable with a diffraction grating. The effects of cavity-length change on oscillator performance are also examined and it is found that the grating can give a valuable stabilizing influence by suppressing cavity-length-induced frequency-pulling effects. Extension of the use of gratings from the picosecond to the femtosecond regime is also considered
Tuning of a synchronously pumped optical parametric oscillator via a four-plate birefringent filter
No full textThe performance of a synchronously pumped optical parametric oscillator based on periodically poled lithium niobate with an appropriately designed birefringent filter is described. Design considerations for the suppression of subsidiary transmission maxima to maximize tuning in these high-gain devices are presented
Room temperature infrared-laser-induced upconversion in Nd<sup>3+</sup> doped Ta<sub>2</sub>O<sub>5</sub> waveguides
No full textThe room temperature infrared to visible upconversion properties of Nd3+ doped Ta2O5 rib waveguides deposited on a silica substrate have been investigated in the 720-900 nm excitation range. Two possible upconversion mechanisms exist at different excitation wavelengths. The main one is due to energy transfer upconversion and results in the population of the 4G7/2 level. Radiative relaxations from this level to the 4I9/2, 4I11/2 and 4I13/2 multiplets produce visible emission bands in the green, orange and red regions. Excited state absorption from the 4F3/2 to the 2P1/2 state can also occur, giving rise to a blue emission band (2P1/2 to 4I9/2). A rate equation analyses supports the proposed mechanisms
Use of a birefringent filter for tuning a synchronously pumped optical parametric oscillator
No full textDesign considerations are presented for birefringent filters suitable for use as tuning elements in synchronously pumped optical parametric oscillators. A particular design aspect that is important, since typical gains are rather high, is the adequate suppression of subsidiary transmission maxima, in order to maximize the tuning range. Results are presented on the performance of a picosecond synchronously pumped optical parametric oscillator based on periodically poled lithium niobate with an appropriately designed four-plate birefringent filter
Agile tuning of a synchronously pumped optical parametric oscillator using a diffraction grating
No full textA synchronously pumped optical parametric oscillator (SPOPO) incorporating an intracavity diffraction grating allows agile tuning (compared with temperature tuning of the nonlinear crystal). Singly resonant operation very close to degeneracy is also readily achieved. We have previously confirmed that the use of the grating is compatible with high power operation (up to 1.6 W of signal output demonstrated)
Synchronously pumped mid-infrared CdSe optical parametric oscillator
No full textSynchronously pumped optical parametric oscillators (SPOPOs) are efficient sources of tunable ultrashort pulses, with low threshold average power requirements, since gain is defined by peak power. An attractive material for such devices is cadmium selenide (CdSe) due to its high nonlinearity (d(31) = 18 pm/V), wide transparency range (0.75-25 µm) and high optical quality. Previous efforts involving CdSe in OPOs have been restricted to angle-tuning, and using Q-switched pump sources. We present here the first continuous-wave, mode-locked SPOPO based on non-critically phase-matched (NCPM) CdSe, with agile tuning of the idler over the range 9.1-9.7 µm, the longest wavelength achieved using a SPOPO to date. Pump-wavelength-tuning over a wide range (necessary for the NCPM arrangement) was provided by the signal output of a periodically poled lithium niobate (PPLN) SPOPO, operating close to degeneracy using a single PPLN grating period. The use of a diffraction grating to tune the signal of the PPLN SPOPO was a key factor in obtaining clean, single-frequency pump conditions, with tuning achieved by simple grating rotation
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