Optimum laser power and pulse length for recording of magneto-optical media

Abstract

This paper discusses the relationship between optimum laser power and pulse length to obtain the maximum signal amplitude in pulse position modulation magneto-optical (MO) recording. The American National Standards Institute standard (X3B11) for 89-mm disks contains an expression for the maximum allowable optical-pulse power incident at the surface of the recording disk as a function of laser-pulse length: Pw=C[(1/tw)+(1/(tw)1/2], where C=75, Pw is the power in mW, and tw is the laser-pulse duration in nanoseconds. This expression was derived empirically, with C a media characteristic (set to 75 in the standard). To evaluate the adequacy of this empirical equation, disks from five different MO disk suppliers were evaluated for write performance. Having examined different metrics to determine optimum write power for a given laser-pulse length, the power producing the maximum signal amplitude for 1.56-μm mark spacings was selected as the performance criterion. Signal amplitude maximizes because of the competition between mark size and intersymbol interference. The value of the constant in the equation was determined for all media tested. The purpose of this paper is twofold. First, we report the results of our experiments confirming the equation across a broad range of laser powers, pulse lengths, and media types. Second, we modeled the thermal properties of the media and the optical read-back process to explain the empirical relationship among signal amplitude, write power, and pulse length.