Quadrature-phase noise penalties of optically and electro-optically phase-locked lasers

Focussing particularly on solid-state laser systems, the phase-noise penalties of laser injection-locking and electro-optical phase-locking are derived using linearised quantum mechanical models. The fundamental performance limit (minimum achievable output phase noise) for an injection-locked laser (IJL) system at low frequencies is equal to that of a standard phase-insensitive amplifier, whereas, in principle, that of a phase-locked laser (PLL) system can be better. At high frequencies, the output phase noise of the IJL system is limited by that of the master laser, while that of the PLL system tends to a weighted sum of contributions from the master and slave laser fields. Under conditions of large amplification, particularly where there has been significant attenuation, the noise penalties are shown to be substantial. Nonideal photodetector characteristics are shown to add significantly to the noise penalties for the PLL system. (C) 2005 Elsevier B.V. All rights reserved.

Lasers - An effective artificial source of radiation for the cultivation of anoxygenic photosynthetic bacteria

The laser diode (LD) is a unique light source that can efficiently produce all radiant energy within the narrow wavelength range used most effectively by a photosynthetic microorganism. We have investigated the use of a single type of LID for the cultivation of the well-studied anoxygenic photosynthetic bacterium, Rhodobacter capsulatus (Rb. capsulatus). An array of vertical-cavity surface-emitting lasers (VCSELs) was driven with a current of 25 mA, and delivered radiation at 860 nm with 0.4 nm linewidth. The emitted light was found to be a suitable source of radiant energy for the cultivation of Rb. capsulatus. The dependence of growth rate on incident irradiance was quantified. Despite the unusual nearly monochromatic light source used in these experiments, no significant changes in the pigment composition and in the distribution of bacteriochlorophyll between LHII and LHI-RC were detected in bacterial cells transferred from incandescent light to laser light. We were also able to show that to achieve a given growth rate in a light-limited culture, the VCSEL required only 30% of the electricity needed by an incandescent bulb, which is of great significance for the potential use of laser-devices in biotechnological applications and photobioreactor construction. (c) 2006 Wiley Periodicals, Inc.