Studies for estimation method of nonlinear optical crystals by using phonon imaging technique

在本工作中，我们的目标是利用我们开发的声子-极化子成像技术，通过检测缺陷引起的声子散射等来估计晶体质量。我们对LiTaO_3进行了成像实验。对传播极化子波包的声子产生和监测进行了成像。为了探测产生的声子-极化子波包，我们可以在所用脉冲的时间分辨率范围内实时构建波包的图像。声子偏振实际上是折射率的调制，因此是相位对象。由于我们的探测能力只对光的强度敏感，通常不可能探测到散射光的相位，但利用塔尔博特效应可以实现从相位信息到强度信息的转换。通过这种特殊的安排，我们成功地实时捕获了声子极化波包的干涉。我们还可以在一定程度上控制传播声子极化子波包的振幅。所得结果对声子光谱学的研究有很大的贡献，并为声子光谱学的研究指明了新的方向。利用类似的四波混频技术，我们可以通过声子散射和激子-激子相互作用来估计块状氮化镓的样品质量，并发现了异质激子。异质双激子由重空穴和轻空穴激子组成，我们首次在GaN中发现了异质双激子。

Im present work, we aimed the estimation of the crystal quality via the detection of the phonon scattering by the defect and so on by using our developed phonon-polariton imaging technique. We have performed the imaging experiment for the LiTaO_3. The phonon generation and monitoring of the propagating polariton wavepackets have been imaged. Illuminating the delayed pulse into the crystal in order to probe the generated phonon-polariton wavepackets, we could construct the image of the wavepackets at the real time within the temporal resolution of the used pulse. The phonon polariotn is really the modulation of the refractive indices and therefore the phase object. Although it is impossible usually to detect the phase of the scattered light since our detection ability is sensitive only to the intensity of the light, the conversion from the phase information to the intensity information can be achieved by using Talbot effect. We have succeeded to capture the interference of the phonon polariotn wavepackets at the real time via the special arrangement. Also we could control the amplitude of the propagating phonon polariton wavepacket within some extent. The obtained results can contribute greatly to the phonon spectroscopy and indicated the new direction of the research. By using the similar four-wave mixing technique, we could estimate the sample quality of the bulk GaN, which is the promising material for the laser diode and so on, via the phonon scattering and exciton-exciton interaction, and found the heterobiexciton. The hetero biexciton consists of the heavy-hole and light-hole excitons and we found the heterobiexciton in GaN for the first time.