In the past decade optical recording media has become a subject of extensive scientific and industrial interest. Good stability

high optical sensitivity

high storage densities

and short access time for optical storage are very important. Azobenzene derivatives are typical materials displaying a reversible photoismerization and are of great potential application as optical information storage media and optical switching systems

[1~4]

. The incorporation of photoisomerizable azobenzene molecules in polymer matrix has been the trend of current research in the area of optical information storage materials because of the mutual exploitable characteristic performances

that is

the ease of device fabrication and the photoreponsiveness of azobenzene units

which can trigger property changes as a result of the conformational change of the molecules. In the previous work

novel azo dye grafted polyurethane (HSANB/PU) has been synthesized and characterized. In this study we report the laser-induced photoismerization property of this graft polymer. The UV-vis absorption spectrum of HSANB/PU film is shown in Fig.1

from which we can see that there are two absorption peaks at 320nm and 500nm

which attribute to cis-form and trans form of HSANB/PU respectively. Generally speaking

the absorption peak of trans form azo compound is at 440nm or so

however this peak shifts to nearly 500nm mainly because of the conjugating effect of benzene and naphthalene ring. Therefore Nd:YAG laser with the output wavelength at 532nm is used to induce the photoisomerization of the polymer film because it is in the resonance region. The spectrum of absorption versus time of HSANB/PU irradiated by 532nm laser with power density of 40mW/cm

2

is shown in Fig.2

which shows that absorption at 520nm decreased

while absorption peak at 360nm increased when the sample is irradiated by the given laser

which indicated the trans-cis transition of the azo compound. Moreover the absorption at 520nm decreased steadily and the absorption increased steadily while the irradiation time ranges from 0～15min. The spectrum of absorption versus power density of HSANB/PU irradiated by 532nm laser for 60s is shown in Fig.3

which shows that the absorption at 520nm decreased steadily and the absorption increased steadily while the irradiation power density ranges from 2～40mW. The effect of intensifying irradiation power is equivalent to that of prolonging irradiation time. Moreover the photoisomerization threshold of the material is only 2mW/cm

2

.