Atomic Layer Thermopile Materials, Laser Induced Thermoelectric Voltage Measurement And Applications

In 1999, X. H. Li, et al., found that La_1-xCa_xMnO₃ film on tilted SrTiO₃ substrate could generate so-called laser induced thermoelectric voltage (LITV) when exposed in pulsed laser beam. Further experiments showed that this LITV effect could be observed in this kind of thin film from far infrared up to ultra-violet. However, there are still a lot of things to be done from practical point of view, for instance, which kind of material has the similar effect? Which wavelength range will be more favorable for a certain material? How about the material, therefore the LITV signal, responded to environmental temperature when used as light detector? All of which need to deal with and systematically investigate. Of course, it is the main purpose of this thesis.First of all, the thin films of La_1-xCa_xMnO₃ (LCMO), La_1-xSr_xMnO₃ (LSMO), La_1-xPb_xMnO₃ (LPMO) and La_1-xSr_xCoO₃ (LSCO) were grown on vicinal-cut LaAlO₃ substrate by pulsed laser deposition (PLD) technique, and two methods were employed to measured LITV signals for pulsed laser and continuous laser respectively. The results showed that the peak value of LITV signal (Up) had a closely linear dependence on incident laser power or energy, mean the time, the sensitivity and response time were strongly affected by the wavelength of incident laser. For example, in the case of LCMO, it was most sensitive to 532nm, 632.8nm, and 808nm, but had largest response time, and the situation was just opposite in the case of LSCO. Furthermore, it was found that the highest sensitivity was reached when the wavelength of laser was 632.8nm for all of LCMO, LSMO and LSCO, and lowest sensitivity for 808nm. However, for LPMO, it displayed a different behavior, that is, the lowest sensitivity was corresponding to 532nm, which may reflect the differences in absorption coefficient a₀ of these materials.From the aspect of light detecting, the environmental temperature could be also a factor influencing the stability of LITV signal. To understand it, we measured the temperature coefficient of resistance (TCR) of LCMO, LPMO and LSCO thin films. The results showed that TCR was lowest and positive for LSCO, and largest (but negative) for LCMO, the TCR of LPMO was also positive. Taking into account of the differences in sensitivity, response time, as well as TCR, the photon-sensitive unit could be selectedaccording to measurement demand. Therefore, it was beneficial for powermeter design and manufacture.Finally, in this thesis, the features of the third generation of powermeter based LITV effect were posed and discussed. Summarily, the third generation powermeter could display the real-time LITV signal for each laser pulse; it could record Up for each laser pulse; for a number of laser pulses, it could calculate and display the maximal U_p, minimal Up, average of Up, and the summation of Up. From this point of view, the third generation powermeter is versatile, multifunctional, easy-operated for measurement, which is very important for real-time probing the fluctuation of laser energy, improving the stability of laser beam. It also provided many useful data for analysis of ophthalmic operation.