By use of self-developing more-information measurement instrument, stability under illumination of
transmission-mode GaAs photocathode sealed in the third generation intensifier was researched and analyzed. The
spectral response curves under ebb-illumination 10<i>lx</i> and strong-illumination 100<i>lx</i> were obtained with illumination time.
The results show that during initial several weak illuminations photocathode behaves no obvious decay and a maximum
sensitivity was achieved, while under intense illumination the sensitivity of photocathode began to decrease largely at the
first illumination. It was also found that under intense illumination the peak wavelength moved towards short-wave and
peak response decreased, which show that the ability of long-wave response of photocathode is decreased. The
performance parameters of GaAs photocathode were estimated by curve imitate. The result indicated that the variation of
surface escape probability with illumination time is the direct cause of instability of photocathode under illumination, at
the same time, it was found that the illumination increased the ion bombardment probability in GaAs tube, it was the
reason for the decline of the cathode sensitive. The Cs quantity on cathode surface and the purge degree of cathode
subassembly were the important factor to the cathode stability.
Based on the research of the standard second generation, the high capability third generation, the exceeding third
generation and the fourth generation, the spectral response of the third generation LLL was carried out using a
self-developing spectral response measurement instrument. Spectral response characteristics of third-generation LLL
tube were obtained, and the material performance parameters of GaAs photocathode were calculated by curve simulation
method. On-line measurement of GaAs photocathode after high-temperature activation and low-temperature activation
was carried out, the results showed that spectral response in the whole response waveband decreased after indium seal,
and long wave responsibility was most obviously influenced. Decrease was large, cut-off wavelength and peak value
wavelength move towards short-wave, peak response value and integral sensitivity decreased, and the final spectral
response curve became flat. By calculating photocathode parameters, it was found that indium seal, lead to the variations
of surface activation layers of photocathode, and the long wave responded and sensitivity decreased accordingly. The
influence factors on the surface activation layers during indium seal were also analyzed.