A new spectroscopic method using a multimode tunable blue diode laser and direct absorption spectroscopy is developed to detect trace amount of nitrogen dioxide (NO₂) gas. The method produces distinctive signatures for NO₂ absorption that are utilized to accurately measure the gas concentration. The NO₂ signatures are obtained by measuring the transmission through a calibrated NO₂ gas sample as a function of laser injection current at a fixed laser temperature. These transmission curves are also calculated from the NO₂ absorption cross section and laser emission spectra. The measured and calculated transmission curves are found to agree reasonably well within 5%. In this study, two different blue diode lasers emitting around 445 nm are investigated. For both lasers, a detection limit of about 0.1 ppm can be achieved in a 40-cm long gas cell under standard atmospheric conditions.

为了检测痕量的二氧化氮（NO ₂）气体，开发了一种使用多模可调蓝光二极管激光器和直接吸收光谱法的新光谱法。该方法产生了独特的NO ₂吸收特征，可用于精确测量气体浓度。通过在固定的激光温度下测量经过校准的NO ₂气体样品的透射率作为激光注入电流的函数，可以获得NO ₂标记。这些传输曲线也由NO ₂计算得出吸收截面和激光发射光谱。发现测量和计算的透射曲线在5％以内相当吻合。在这项研究中，研究了两种不同的发射波长约445 nm的蓝色二极管激光器。对于这两种激光器，在40厘米长的气室中，在标准大气条件下，检测极限约为0.1 ppm。