Tran C D, Gao G H
Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201, USA.
Anal Chem. 1996 Jul 1;68(13):2264-9. doi: 10.1021/ac9600262.
A novel light source for the near-infrared region which has the highest intensity and widest spectral bandwidth of all near-IR light sources has been developed. The system is based on a single-mode fiber (about 18 m long) doped with Er3+ ion. The doped ion produces amplified spontaneous emission (ASE) in the near-IR region (from 1500 to 1600 nm) when it is excited by a diode laser at 980 nm. Because the diode laser is fusion-spliced directly to the doped fiber, the system is compact, all-solid-state, reliable, and stable and requires little maintenance. Its ASE output intensity was found to be comparable with those of diode lasers currently available for this near-IR region and is much higher than those of conventional halogen-tungsten lamps and the so-called (high-intensity) superluminescent light emitting diodes (SLEDs). Its spectral bandwidth is, however, much wider than those of the diode lasers and the SLEDs. Even higher intensity can be obtained from the doped fiber when a low-intensity (1 mW) light from a 1550-nm laser diode is introduced into the doped fiber. The intensity is enhanced (up to 7 times compared to the ASE) because the input light is amplified by the doped fiber. Furthermore, the output intensity of this erbium-doped fiber amplifier (EDFA) can be appropriately adjusted to provide relatively higher output intensity at any range of wavelengths (within this 1500-1600-nm region) by simply changing the temperature and/or the driven current of the input diode laser. Subsequently, an acoustooptic tunable filter was used to provide a means to spectrally tune the EDFA rapidly and to develop an all-solid-state, compact near-IR spectrophotometer which not only is very sensitive, stable, and reliable but also has a very high throughput. This spectrophotometer can detect water in ethanol at a limit of detection of 10 ppm. More importantly, the high through-put makes it possible to use the instrument to measure spectra of highly absorbing samples (e.g., absorption spectrum of 1.0 M Pr3+ aqueous solution through four sheets of paper); measurements which are currently not possible with halogen-tungsten lamp-based spectrophotometers.
已研发出一种新型近红外区域光源，它在所有近红外光源中具有最高强度和最宽光谱带宽。该系统基于一根掺杂了铒离子（Er3+）的单模光纤（约18米长）。当掺杂离子被980纳米的二极管激光器激发时，会在近红外区域（1500至1600纳米）产生放大自发辐射（ASE）。由于二极管激光器直接与掺杂光纤熔接，该系统结构紧凑、全固态、可靠且稳定，几乎无需维护。研究发现，其ASE输出强度与目前该近红外区域可用的二极管激光器相当，且远高于传统卤钨灯和所谓的（高强度）超发光发光二极管（SLED）。然而，其光谱带宽比二极管激光器和SLED的要宽得多。当将来自1550纳米激光二极管的低强度（1毫瓦）光引入掺杂光纤时，可从掺杂光纤获得更高强度。强度会增强（与ASE相比提高多达7倍），因为输入光被掺杂光纤放大。此外，通过简单改变输入二极管激光器的温度和/或驱动电流，这种掺铒光纤放大器（EDFA）的输出强度可得到适当调整，从而在任何波长范围（在这个1500 - 1600纳米区域内）提供相对较高的输出强度。随后，使用声光可调滤波器提供一种快速对EDFA进行光谱调谐的方法，并开发出一种全固态、紧凑的近红外分光光度计，该分光光度计不仅非常灵敏、稳定且可靠，而且具有非常高的通量。这种分光光度计能够检测乙醇中的水，检测限为10 ppm。更重要的是，高通量使得使用该仪器测量高吸收样品的光谱成为可能（例如，透过四张纸测量1.0 M Pr3+水溶液的吸收光谱）；而目前基于卤钨灯的分光光度计无法进行此类测量。
