本研究以射頻氮氣電漿為研究對象，建立一套以雙側位置感測探測器(duolateral position sensing detector， PSD)為核心之非侵入式光學偏折量測架構，用以分析低壓射頻氮氣電漿中折射率隨操作條件改變之響應。由於弱電離電漿之折射率同時受到中性氣體背景與自由電子響應影響，本研究以PSD量測雷射光束通過電漿區後之兩光點距離變化，並以Langmuir探針作為輔助量測工具，取得主電漿區離子密度；在準中性與弱電離假設下，將其近似為電子密度，再結合中性氮氣背景折射率與自由電子折射率修正公式，建立參考總折射率，作為PSD光學量測校正與趨勢比較之依據。 PSD光學實驗結果顯示，在固定射頻功率下改變氮氣流量及固定氮氣流量下改變射頻功率時，量測所得之兩光點距離則隨操作條件不同而有所改變，表示不同操作條件會造成雷射光束通過電漿區後之光學響應改變。經折射率計算後，PSD所得折射率變化趨勢與考慮中性氣體背景及自由電子修正後之參考總折射率趨勢相符。結果亦顯示，在本研究之低壓弱電離氮氣電漿條件下，總折射率主要受中性氣體密度變化主導，自由電子項則提供相對較小之負修正。 綜合而言，本研究完成射頻氮氣電漿下PSD光學偏折量測與折射率分析流程之建立，並透過Langmuir探針結果輔助驗證其變化趨勢。PSD光學量測結果可反應氮氣流量改變所造成之折射率響應，顯示其具備作為射頻氮氣電漿折射率趨勢監測方法之可行性。然而，由於PSD量測結果仍可能受到光路準直、氣體流場、腔體玻璃變形及環境振動等因素共同作用後之結果等因素影響，因此本研究成果較適合作為折射率趨勢監測之初步驗證，而非絕對折射率之精密量測。;This study investigates the refractive-index response of low-pressure radio-frequency nitrogen plasma using a non-invasive optical beam-deflection measurement system based on a duolateral position sensing detector (PSD). Since the refractive index of weakly ionized plasma is affected by both the neutral gas background and the free-electron response， the PSD was used to measure changes in the distance between two laser spots after the beams passed through the plasma region. A Langmuir probe was employed as an auxiliary diagnostic tool to obtain the ion density in the main plasma region. Under the assumptions of quasi-neutrality and weak ionization， the ion density was approximated as the electron density and combined with the neutral nitrogen refractive index and free-electron correction to establish a reference total refractive index for PSD calibration and trend comparison. The results show that the measured laser spot distance varied with nitrogen flow rate at fixed RF power and with RF power at fixed nitrogen flow rate， indicating that different operating conditions altered the optical response of the plasma. After refractive-index calculation， the PSD-derived refractive-index trend was consistent with the reference total refractive index. Under the low-pressure weakly ionized nitrogen plasma conditions used in this study， the total refractive index was mainly dominated by changes in neutral gas density， while the free-electron term provided a relatively small negative correction. Overall， this study establishes a PSD-based optical beam-deflection procedure for refractive-index analysis in RF nitrogen plasma. The results demonstrate the feasibility of using PSD optical measurement for monitoring refractive-index trends. However， because the measurement may be affected by optical alignment， gas flow distribution， chamber window deformation， environmental vibration， and other combined factors， the proposed method is more suitable for preliminary trend monitoring than for precise absolute refractive-index measurement.
