低温对中波红外带通滤光片光谱特性的影响

Spectral characteristics of MWIR band-pass filters at cryogenic temperature

为考察滤光片在低温环境下的可靠性,镀制了Ge基和宝石基中波带通滤光片,分别实施了5min、15min、25min、35min、120min、300min的液氮低温试验,并测试出其透过率曲线,考察低温对其光谱特性及膜层牢固度的影响。带通滤光片通带区透过率随低温时间增长有逐渐下降趋势,中心波长出现13nm的微小偏移,是所镀制的膜料高、低折射率相对变化使中心波长和截止波长的比值发生变化所致。Ge基材料对温度更为敏感,在由常温到低温过渡期间,Ge基中波滤光片通带透过率降低幅度比宝石基底的中波带通滤光片大10%。在300min以内的低温环境下,2种中波红外带通滤光片均未出现膜层脱落现象。

In order to research the reliability of filters at cryogenic temperature,Ge-based and sapphire-based mid-wave infrared(MWIR)band-pass filters were coated,and the experiments at cryogenic temperature for 5min,15 min,25min,35 min and even more than 300 min were done,respectively,the transmittance curves were showed.Furthermore,the impact of cryogenic temperature on the spectral characteristics and fastness after were studied.The transmittance of passband zone reduces with the time increasing at cryogenic temperature,and there is a small shift of 13 nm for center wavelength,resulted from the relative variation of the high and low refractivities of deposited coatings which can induce the ratio between center and cut-off wavelengths to change.Compared to the sapphire substrate,Ge substrate is more sensitive to temperature,so the fall range of transmittance shows obvious(about more than 10%)when the band-pass filters transit from room temperature to cryogenic temperature.The fastness of both the Ge-based and sapphire-based MWIR band-pass filters have never been damaged at cryogenic temperature for no more than 300 min.