We investigate the efficiency of interstellar polarization p _ { \lambda } / A _ { \lambda } , where p _ { \lambda } is the fractional linear polarization and A _ { \lambda } is extinction , in 14 lines of sight as a function of wavelength \lambda .
We have used the data of lines of sight to the Pleiades cluster obtained with the low-dispersion spectropolarimeter HBS as well as those in literature .
It is found that the polarization efficiency p _ { \lambda } / A _ { \lambda } is proportional to \exp ( - \beta / \lambda ) in wavelength \lambda \approx 0.4 \sim 0.8 \micron , where \beta is a parameter which varies from 0.5 to 1.2 \micron .
We find that \beta is negatively correlated with the dust temperature deduced from infrared data by Schlegel et al. , suggesting that the polarization efficiency is higher in short wavelength for higher temperature .
According to the alignment theory by radiative torques ( RATs ) , if the radiation is stronger , RATs will make small grains align better , and the polarization efficiency will increase in short wavelength .
Our finding of the correlation between \beta and the temperature is consistent with what is expected with the alignment mechanism by RATs .