A diode-laser-pumped, Er³⁺-doped fibre laser operating at 1.57µm

Erbium-doped fibers show promise as stable narrow-linewidth laser sources and optical amplifiers operating in the third telecommunications window around 1.55µm Diode laser pumping is possible using the weak pump-band located at 807nm, although this band suffers severely from excited-state absorption (ESA), which reduces gain and pump efficiency. At the low pump power available from diode lasers the Er3+ behaves as a quasi four-level system. However, by codoping the core glass heavily with Yb3+, it is possible to excite the Er3+ ions indirectly using energy transfer. The Yb3+ provides an intense broad pump-band centered at 900nm, which reduces the effect of ESA. As a consequence of the resulting higher pump efficiency, the laser will oscillate at the required shorter wavelengths

+21dBm erbium power amplifier pumped by a diode-pumped Nd:YAG laser

Efficient energy transfer has been demonstrated in an Er/Yb co-doped phosphorus doped silica fiber for the first time. This has indirectly allowed the use of reliable, high-power AlGaAs diode laser arrays as the semiconductor pump source through the use of a diode-pumped Nd:YAG (DPL) laser operating at 1064 nm. Small signal gains of 42 dB and output powers of 71 mW (+18.5 dBm) have been observed with a single DPL. Bidirectional pumping with two DPLs has yielded an output power of 130 mW (+21 dBm)

Highly tunable and efficient diode pumped operation of Tm³⁺ doped fibre lasers

The characteristics of a Tm3+ doped fibre laser pumped by a laser diode are reported. Operating at a wavelength of 1.94µm the laser had a threshold of 4.4mW, a launched power slope efficiency of 17% and 1mW output power. Measurements on the tuning rang of Tm3+ are presented and lasing is found to be possible from 1.65-2.0µm, the specific range depending on the fibre type. The largest range for a single laser was 300nm

Detailed characterization of Nd³⁺ doped SiO₂ - GeO₂ glass fibre lasers

Several basic parameters of Nd3+ in a SiO2 - GeO2 glass fibre have been determined. The stimulated emission cross-section for the 4F3/2 to 4I11/2 transition has been evaluated experimentally both by a laser technique and spectroscopically. Comparison is made between the two methods and a nonradiative decay process inferred. The efficiency of the 800nm pump band was determined from measurements of laser slope efficiencies. Branching ratios for the different fluorescent bands have been measured and cavity losses determined

Langerhans cells in the development of skin cancer: A qualitative and quantitative comparison of cell markers in normal, acanthotic and neoplastic ovine skin

The distribution of Langerhans cells in normal, acanthotic and neoplastic ovine epithelium was examined using the enzyme marker Acetylcholinesterase (AchE) and monoclonal antibodies (MoAb) to CD1 (20.27) and MHC Class It (49.1 and 28.1) molecules. In normal skin, where Langerhans cells were regularly spaced within the basal layer, qualitative observations and direct pairwise testing showed that AChE was superior to the MoAb in detecting these cells. Significantly more (P < 0.01) dendritic cells were also detected with MoAb 49.1 than MoAb 20.27 or 28.1, suggesting differential expression of MHC Class II subsets and the presence of CD1– MHC Class II+ granule– dendritic cells in sheep analogous to indeterminate cells of man. In acanthotic skin, compared to normal skin, Langerhans cells were less numerous, irregular and more suprabasal in distribution and their morphology was occasionally swollen and indistinct. No difference was seen in the ability of AChE and MoAb in detecting Langerhans cells, however pairwise testing of markers did demonstrate that significantly more (P < 0.05) cells without dendritic processes were stained with MoAb 49.1 than with 20.27 or 28.1. In all squamous cell carcinomas examined dendritic cells that stained for ACHE, CD1 or MHC Class II antigens were concentrated at the peripheral areas of neoplastic epithelium. Many dendritic cells were detected with MoAb to MHC Class II antigens, whereas CD1 and AChE positive dendritic cells were rare in tumor bearing tissue. The quantitative differences in the immunohistochemical staining of Langerhans cells between normal, acanthotic and neoplastic epithelium were consistent with ultrastructural studies. When compared with those of a newborn lamb, which had had very little exposure to antigens or ultraviolet radiation (UVR), the Langerhans cells of the aged sheep were deformed and contained far fewer Birbeck granules. The abnormalities were progressively more severe in acanthotic and neoplastic skin. These observed changes may have resulted from UVR induced damage and may be indicative of impaired function involved in the development of skin cancer

Yb³⁺ sensitised Er³⁺ doped, silica-based optical fibre with ultra-high transfer efficiency

Efficient 1.54µm emission under 1064nn excitation of Er3+ codoped silica fibre is reported. The energy transfer efficiency from Yb3+ to Er3+, of at least 85%, even under high inversion, is comparable to that in multicomponent glass fibres. Fibre design parameters are discussed and results presented. Small signal gain of ~45 dB is also measured and a power amplifier giving 145mW output power demonstrated.<br/

Pseudomonas pseudomallei infection in camels

We read with interest the report on melioidosis in camels by Bergin and Torenbeeck (1991). In January 1990, we isolated Pseudomonas pseudomallei from a camel at Mingela, northern Queensland, which had severe, purulent bronchopneumonia. This camel differed in its clinical presentation from the animal described by Bergin and Torenbeeck (1991) from which P pseudomallei was isolated by the Rockhampton Veterinary Laboratory. The attending veterinarian found the 8-year-old bull camel to be pyrexic, distressed, dehydrated and disinterested in its environment. Ataxia, particularly of the hind limbs, was evident when attempts were made to move it

Pseudomonas pseudomallei infection in camels

We read with interest the report on melioidosis in camels by Bergin and Torenbeeck (1991). In January 1990, we isolated Pseudomonas pseudomallei from a camel at Mingela, northern Queensland, which had severe, purulent bronchopneumonia. This camel differed in its clinical presentation from the animal described by Bergin and Torenbeeck (1991) from which P pseudomallei was isolated by the Rockhampton Veterinary Laboratory. The attending veterinarian found the 8-year-old bull camel to be pyrexic, distressed, dehydrated and disinterested in its environment. Ataxia, particularly of the hind limbs, was evident when attempts were made to move it