灵敏的基于分布反馈式半导体激光波长调制光声光谱

利用室温下单模运行的近红外半导体二极管激光,报导了波长调制共振光声光谱结合二次谐波探测技术.实验系统应用到乙炔探测,在1个标准大气压和3毫瓦平均光功率以及3毫秒锁相积分时间条件下其探测灵敏度可达10ppm(体积比),归一化到激光功率和系统带宽最小可探测吸收为4.0×10-8Wcm-1/Hz,并且实验中发现系统最佳压力响应值在2.66×104Pa附近.本实验装置可有效的消除光声光谱系统中常见的窗片和光声腔壁吸收入射光而引起的背景噪声.此外,相对于其他方法我们描述的基于半导体激光共振光声光谱具有很大的优点,为进一步发展便利、实用、便携式环境监测仪器奠定了坚实的基础.

Sensitive wavelength-modulated photoacoustic spectroscopy with DFB diode laser

A new approach to wavelengthmodulation resonant photoacoustic spectroscopy is reported with 2nd harmonic detection, which incorporates room-temperature single mode distributed feedback (DFB) diode laser in the near-infrared. We demonstrate the technique with acetylene detection, yielding a sensitivity limit is about 10 ppm v of acetylene at atmosp heric pressure with 3ms time constant and 3 mW average optical power, which corresponds to the minimum detectable absorption coefficient normalized by laser power and bandwidth is 4.0×10-8 Wcm-1/Hz. Moreover, the optimal pressure condition of buffer gas (N2) has been found to be near 2.4×104 Pa for our photoacoustic system. The present system can effectively eliminate the background signal generated by absorption of the cell windows and by the walls of the sample chamber whose spatial and temporal character are clearly distinct from the resonant wave. We believe that the resonant PA system based on diode laser described here offers substantial advantages over other methods and appears promising as a basis for developing convenient, robust, portable instruments for environmental monitoring and process control.