Temperature Dependence Of Laser Cooling Efficiency For A Microcantilever

The study of photothermal coupling and temperature dependence of photothermal cooling efficiency were studied in a microcantilever based cavity in this dissertation. Our experimental research is based on the experimental platform for magnetic resonance force microscope (MRFM) to set up of a suitable optomechanical experiment platform for the study of optomechanical coupling. By using the high sensitivity of microcantilever beam and the optical fiber end to construct a low finesse FP optical cavity, photothermal coupling effect of optical cavity system was studied. Experiments showed that the main coupling mechanism in a low finesse optical cavity is photothermal coupling. When optical cavity is in blue detuning, the dynamics of the mechanical resonator can be modified apparently via optomechanical coupling and the thermal oscillation of cantilever can be suppressed. In photothermal coupling process, with the increase of laser power, the laser absorption heating effect of microcantilever, higher order mechanical modes’contribution and optical bistability will have an effect on the photothermal cooling efficiency. In order to improving the photothermal cooling efficiency of the microcantilever, we carried out a research with experimental and theoretical analysis on the optimal photothermal cooling. Experimental data from77K to298K showed that temperature has an obvious influence on photothermal cooling efficiency and the maximum of cooling efficiency can be reached at a certain temperature. In the process of experiment, the cantilever is silicon microcantilever beam which is double gold coated. According to two kinds of material properties by two materials in the experimental temperature, we found that in the experiment the certain temperature is100K, which can achieve the maximum of photothermal cooling efficiency. What is more, the photothermal cooling efficiency at298K is10percent of that at100K.We firstly researched the influence of temperature on the photothermal cooling efficiency experimentally, and the power spectral density of micro cantilever was measured and analyzed by changing the experimental temperature. Then using a simulation analysis verified our experimental results theoretically. Additionally, we deduced that the relationship between the photothermal cooling efficiency and delayed response time τph. When the optimal photothermal cooling condition ω0τPh=1was satisfied, it can be obtained the maximum photothermal cooling efficiency. The results of theory simulation confirmed the correctness of our experimental results. This research indicated a way to improve the photothermal coupling efficiency which can apply for high sensitivity measurement of force microscopy.