Studies on Lattice Vibrations of Dielectric and Magnetic Crystals by Hyper-Raman Scattering.

The experimental arrangement set up for the measurement of the.hyper-Raman spectrum is as follows.The 1.06&lt；micro&gt；m line from an acousto-optically Q-switched Nd：YAG laser(NEC)was used for the excitation。The repetition rate was set to between2 KHz(Pulse Width150 Ns)and 6 KHz(200 Ns)。A peak power between 3 and 50 KW was employed.The laser beam was focussed into the sample by a f=5.cm lens。The scattered light in the 90°geometry was dispersed by a polychromator(JASCO TRS-501)and detected by the intensified photodiode array detector(Tracor Northern)with a controller.In this multichannel detection system the frequency region of approximately230&lt；cm^(-1)&gt；is measured simultaneously.In the hyper-Raman spectrum below280&lt；cm^(-1)&gt；of SrTi&lt；O_3&gt；crystal.Three bands at88，175and266&lt；cm^(-1)&gt；are observed，which correspond to the&lt；nu_1&gt；(TO，&lt；f_(1u)&gt；)，&lt；nu_1&gt；(LO，&lt；f_(1u)&gt；)+&lt；nu_2&gt；(TO，&lt；f_(1u)&gt；)and&lt；nu_4&gt；(&lt；nu_4&gt；)F_(2u)&gt；)respectively。These bands were used for the adjustment and wavenumber calibration of our spectrometer.In CsCa&lt；C1_3&gt；，the following five hyper-Raman bands were observed：76&lt；cm^(-1)&gt；(&lt；nu_1&gt；LO)，114&lt；cm^(-1)&gt；(&lt；nu_2&gt；TO)，142&lt；cm^(-1)&gt；(&lt；nu_2&gt；LO)，267&lt；cm^^(-1)&gt；(&lt；nu_3&gt；TO)and 312&lt；cm^(-1)&gt；(&lt；nu_3&gt；LO)。These are compared with the data obtained from the far-infrared reflection spectrum and a Kramers-Kroning analysis.The hyper-Raman data might be more reliable than the far-infrared data，because(1)the reflectivity measurements depend on the condition of the crystal surface and(2)the data in the low-reflectivity region influence the accuracy of the dielectric function and the TO and LO frequencies calculated from relectivity data by Kramers-Kronig relation.The hyper-Raman spectra of several alkali halides and perovskite chlorides and perovskite chlorides were the far-infrared data，because(1)the reflectivity measurements depend on the condition of the crystal surface and the

The experimental arrangement set up for the measurement of the.hyper-Raman spectrum is as follows.The 1.06 <micro> m line from an acousto-optically Q-switched Nd:YAG laser (NEC) was used for the excitation. The repetition rate was set to between 2 KHz (pulse width 150 ns) and 6 KHz (200 ns). A peak power between 3 and 50 KW was employed. The laser beam was focussed into the sample by a f = 5.cm lens. The scattered light in the 90゜ geometry was dispersed by a polychromator (JASCO TRS-501) and detected by the intensified photodiode array detector (Tracor Northern) with a controller. In this multichannel detection system the frequency region of approximately 230 <cm^(-1)> is measured simultaneously.In the hyper-Raman spectrum below 280 <cm^(-1)> of SrTi <O_3> crystal. three bands at 88, 175 and 266 <cm^(-1)> are observed, which correspond to the <nu_1> (TO, <f_(1u)> ), <nu_1> (LO, <f_(1u)> ) + <nu_2> (TO, <f_(1u)> ) and <nu_4> ( <f_(2u)> ) respectively. These bands were used for the adjustment and wavenumber calibration of our spectrometer.In CsCa <C1_3> , the following five hyper-Raman bands were observed: 76 <cm^(-1)> ( <nu_1> LO), 114 <cm^(-1)> ( <nu_2> TO), 142 <cm^(-1)> ( <nu_2> LO), 267 <cm^(-1)> ( <nu_3> TO) and 312 <cm^(-1)> ( <nu_3> LO). These are compared with the data obtained from the far-infrared reflection spectrum and a Kramers-Kroning analysis. The hyper-Raman data might be more reliable than the far-infrared data, because (1) the reflectivity measurements depend on the condition of the crystal surface and (2) the data in the low-reflectivity region influence the accuracy of the dielectric function and the TO and LO frequencies calculated from relectivity data by Kramers-Kronig relation.The hyper-Raman spectra of several alkali halides and perovskite chlorides were measured.