C. Alegria

Single-frequency, single-mode, plane-polarized ytterbium-doped fiber master oscillator power amplifier source with 264 W of output power

We present a single-frequency, single-mode, plane-polarized ytterbium-doped all-fiber master oscillator power amplifier source at 1060 nm generating 264 W of continuous-wave output power. The final-stage amplifier operated with a high gain of 19 dB and a high conversion efficiency of 68%. There was no evidence of rollover from stimulated Brillouin scattering even at the highest output power, and the maximum output was limited only by the available pump power.

High-energy in-fiber pulse amplification for coherent lidar applications

An Er:Yb codoped fiber amplifier chain for the generation of pulses for coherent lidar applications at a wavelength near 1.5 microm is reported. The final 1.8-m-long power amplification stage had a 50-microm core diameter and yielded a 23-dB energy gain, resulting in 0.29-mJ, 100-ns pulses at a repetition rate of 4 kHz with no Brillouin scattering and an M2 of 2.1.

A 980-nm Yb-doped fiber MOPA source and its frequency doubling

A continuous-wave (CW) master oscillator-power amplifier (MOPA) fiber source, tunable around 978 nm, was frequency-doubled to 488.7 nm. Both the laser and the amplifier were made with cladding-pumped jacketed air-clad Yb-doped fibers. The MOPA generated up to 2.7 W of power in an output beam with an M/sup 2/ value of 1.8. This was frequency-doubled in a periodically poled potassium titanyl phosphate crystal at room temperature, in a single-pass configuration. The generated blue light had a CW power of 18.1 mW, a nearly Gaussian spatial intensity profile, and an M/sup 2/ value of 1.7.

83-W single-frequency narrow-linewidth MOPA using large-core erbium-ytterbium Co-doped fiber

We demonstrate a continuous-wave (CW) single-frequency narrow-linewidth laser at 1552 nm with an output power of 83 W using a master-oscillator power amplifier configuration. A seed from an all-fiber distributed feedback-laser with a linewidth of 13 kHz was polarization scrambled and boosted through a chain of amplifiers in an all-fiber configuration. The last amplification stage consisted of a highly efficient cladding-pumped large-core erbium-ytterbium co-doped fiber which helped increase nonlinear thresholds.

A 43-W C-band tunable narrow-linewidth erbium-ytterbium codoped large-core fiber laser

The authors report a widely tunable and highly efficient cladding-pumped erbium-ytterbium codoped large-core fiber laser, generating up to 43 W of output power at /spl sim/1.5 /spl mu/m with a narrow linewidth (0.16-nm full-width at half-maximum) and a good beam quality (M/sup 2/<1.7). By use of a tunable narrow-band fiber Bragg grating, the laser wavelength was tuned from 1532 to 1567 nm, limited upwards by the tuning range of the fiber grating. The overall slope efficiency was 32% with respect to launched pump power.

Kilowatt-class single-frequency fiber sources

We discuss the dramatic development of high-power fiber laser technology in recent years and the prospects of kilowattclass single-frequency fiber sources. We describe experimental results from an ytterbium-doped fiber-based multihundred-watt single-frequency, single-mode, plane-polarized master-oscillator power amplifier (MOPA) operating at 1060 nm and a similar source with 0.5 kW of output power, albeit with a degraded beam quality (M2 = 1.6) and not linearly polarized. Experiments and simulations aimed at predicting the Brillouin limit of single-frequency system with a thermally broadened Brillouin gain are presented. These suggest that single-frequency MOPAs with over 1 kW of output power are possible. In addition, the power scalability of a simple single-strand fiber laser to 10 kW is discussed.

A 4.3W 977nm ytterbium-doped jacketed-air-clad fiber amplifier

A cladding pumped jacketed-air-clad ytterbium-doped fiber amplifier operating at 977 nm produced 4.3 W of single-mode output power with 300 mW of input power from a diode seed laser. The small-signal gain was 19 dB.

Recent advances in high power fiber lasers

We will review recent progress on cladding-pumped fiber devices with output powers up to the kilowatt level and broad wavelength tunability in the 1 - 2 µm wavelength regime where silica fibers work well.

Beyond 1 kW with fiber lasers and amplifiers

We report recent progress and future prospects of high-power fiber sources in the 1 and 1.5 /spl mu/m spectral ranges, with a 103 W, 1565 nm erbium-ytterbium doped fiber laser as an example. Our emphasis is on diode stack pumping and short fibers with high Brillouin thresholds.

Earnings announcements by UK companies: Evidence of extreme events?

This paper investigates the abnormal share return dispersion occurring when companies announce their interim or final earnings. Whereas, prior research has focused on abnormal returns, little attention has been given to investigating the dispersion of the abnormal returns. We find strong empirical evidence supporting an abnormal dispersion of share returns on event dates. Moreover, we find that these public announcements are sources of extreme share price movements. Our study provides a step forward in identifying factors underlying the leptokurtosis that is traditionally found in time series stock market returns. Our data sample is comprised of interim and full year results for mid-to-large capitalisation UK companies for the period 1984–2005. Consistent with the extant literature on this subject, we find no evidence of market inefficiency around the event date, or straightforward arbitrage opportunities on the event date. However, we find using Paretian statistics that the abnormal return dispersion on the event date is three times higher than on normal non-event days.