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تسجيل مستخدم جديدتحفظ الأوزان المتعددة في كوبر بورات CuB$_2$O$_4$ عبر الانحياز الحاد المشجع الذي يستجل بالإشعاع رامان
Excitation of multiple phonon modes in copper metaborate CuB$_2$O$_4$ via non-resonant impulsive stimulated Raman scattering
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تم التحقق من إثارة أربعة وحدات فونون متوازنة من أنماط مختلفة في الميتابورات النحاسية CuB$_2$O$_4$ عن طريق الانبعاث الشديد المشجع الراماني (ISRS). وتم كشف الفونونات بمراقبة التغيرات في البيريفرنج البصري الخطي باستخدام تقنية الكشف المتوازن (BD). نقارن نتائج تجربة BD-ISRS ببيانات مجموعة من الفونونات الشواردية الرامانية المولودة بشكل طبيعي. نظرا للتوافق الذي تحققناه بين هذين الطريقتين في مدى واسع من ترددات الفونونات من 4 إلى 14 تيراهرتز، يجب أن نتأكد من التناسب الدقيق بين تركيب الفونونات وقواعد الإثارة والكشف المتوقعة. كما يؤثر في هذا التحليل المقارن أيضا الفرق بين الفونونات الغير متوازنة والمتوازنة بشأن مساهمتهم في عملية الانبعاث الراماني. ويسلط الضوء على أهمية نسبة بين تردد وحدة فونون معينة وعرض الطيف الخاص بالطاقة المشجعة والمستشعرة. ونظرا لذلك نظرنا أنه يجب أن نوضح بشكل تحليلي أن مدتي الطاقة المشجعة والمستشعرة التي تستخدم في تجاربنا، التي هي 90 و 50 فولت ثانية على التوالي، تحدد أعلى تردد للوحدات الفونون المثيرة والمحسوسة المتوازنة إلى 12 تيراهرتز، وتحدد أجزاؤها النسبية.
Excitation of four coherent phonon modes of different symmetries has been realized in copper metaborate CuB$_2$O$_4$ via impulsive stimulated Raman scattering (ISRS). Phonons were detected by monitoring changes in the linear optical birefringence using the balanced-detection (BD) technique. We compare the results of BD-ISRS experiment to the polarized spontaneous Raman scattering spectra. We show that the agreement between the two sets of data obtained by these allied techniques in a wide phonon frequencies range of 4-14 THz can be achieved by rigorously taking into account the symmetry of the phonon modes, and the corresponding excitation and detection selection rules. It is also important to account for the difference between incoherent and coherent phonons in terms of their contributions to the Raman scattering process. This comparative analysis highlights the importance of the ratio between the frequency of a particular mode, and the pump and probe spectral widths. We demonstrate analytically that the pump and probe pulse durations of 90 and 50 fs, respectively, used in our experiments, limit the highest frequency of the excited and detected coherent phonon modes to 12 THz, and define their relative amplitudes.
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