We present transmission enhancement of ultraslow light in an
inhomogeneously broadened spectral hole-burning solid medium by using
precedent dummy light. The function of the dummy light is to burn a half-depth
narrow spectral hole in an optically shelved solid system and to maintain
the system optically transparent to the probe light, where the probe must
experiences ultraslow group velocity due to the narrow spectral hole.
The observed transmission increase is as high as 7 times compared with
self-induced ultraslow light [J. Hahn and B. S. Ham, Opt. Express 16, 16723
(2008)], where the transmission enhancement is equivalent to 105 amplification
considering an optical depth of d = 10.