Improving Raman spectroscopy using diode lasers at 785 nm for shifted excitation Raman difference spectroscopy

Abstract

Shifted excitation Raman difference spectroscopy (SERDS) has been successfully demonstrated for separating Raman signals from background interferences. This powerful tool has been applied for in situ applications such as in vivo diagnostics and outdoor investigations. Here, diode lasers are well suited excitation light sources and their compact size and electro-optical efficiency allows integrating them into portable devices such as handheld sensor systems. In the last decade our institute has developed and applied diode lasers for Raman spectroscopy and SERDS at 785 nm. Here, wavelength stabilization is realized using internal frequency selective elements such as distributed feedback (DFB) or distributed Bragg reflector (DBR) gratings. In this contribution, an overview of Raman spectroscopy and SERDS using our diode lasers and diode laser systems emitting at 785 nm will be given. DFB ridge waveguide (RW) lasers providing 0.2 W and wavelength tuning for SERDS via injection current will be discussed. DFB broad area devices with 1 W optical output power suitable for Raman spectroscopy are realized. Dual-wavelength Y-branch DBR-RW diode lasers are developed and show optical powers up to 0.2 W. The devices provide a flexible spectral distance between the two excitation lines via implemented heater elements. Recently, a micro-integrated diode laser based dual-wavelength MOPA at 785 nm with 0.5 W optical power suitable for SERDS has been developed. Laser characteristics and Raman experiments will be presented. The results demonstrate the suitability of these devices for SERDS improving Raman spectroscopy for various applications e.g. under in situ conditions.