Pastel R L, Sausa R C
Appl Opt. 1996 Jul 20;35(21):4046-52. doi: 10.1364/AO.35.004046.
Trace concentrations of NO and NO(2) are detected with a dye laser operating near 454 nm. NO is detected by a (2 + 2) resonance-enhanced multiphoton ionization process by means of NO A(2)Σ+-X(2)Π(0, 0) transitions with miniature electrodes, and NO(2) is detected by a one-photon absorption photoacoustic process by means of NO(2)A¯' (2)B(1)(0, 8, 0)- X¯ (2)A(1)(0, 0, 0) transitions with a miniature microphone. Rotationally resolved excitation spectra show that the spectral resolution is sufficiently high to identify these species at 1 atm. The technique's analytical merits are evaluated as functions of concentration, pressure, and laser intensities. Low laser intensities favor NO(2) photoacoustic detection whereas high laser intensities favor NO ionization. Limits of detection (signal-to-noise ratio 3) of 160 parts in 10(9) for NO and 400 parts in 10(9) for NO(2) are determined at 1 atm for a 10-s integration time. Signal response and noise analyses show that three decades of NO/NO(2) mixtures can be measured with a computational relative error in concentration that is three times the relative error in measuring the NO and NO(2) signals.
利用波长在454nm附近的染料激光器检测痕量浓度的一氧化氮（NO）和二氧化氮（NO₂）。通过（2 + 2）共振增强多光子电离过程，借助小型电极利用NO的A²Σ⁺-X²Π（0, 0）跃迁来检测NO；通过单光子吸收光声过程，借助小型麦克风利用NO₂的A′（2）B₁（0, 8, 0）-X′（2）A₁（0, 0, 0）跃迁来检测NO₂。转动分辨激发光谱表明，在1个大气压下，光谱分辨率足够高，能够识别这些物质。该技术的分析优点作为浓度、压力和激光强度的函数进行评估。低激光强度有利于NO₂的光声检测，而高激光强度有利于NO的电离。在1个大气压下，对于10秒的积分时间，确定NO的检测限（信噪比为3）为10⁹分之160，NO₂的检测限为10⁹分之400。信号响应和噪声分析表明，对于NO/NO₂混合物，可以测量三个数量级，其浓度的计算相对误差是测量NO和NO₂信号时相对误差的三倍。
