Compact external cavity diode lasers

External cavity diode lasers with wavelength-stabilized narrowband emission are developed as excitation light sources for demanding applications such as Raman spectroscopy. These compact light sources with maximum footprints of only 5 mm x 25 mm are realized using micro-optical components. This enables the lasers to be implemented into portable laser systems, suitable for different applications for example in biology, medicine and pharmacy. Developed light sources are continuously applied in food control, locally analyzing the quality of meat. The optical concept for compact external cavity diode lasers is also expanded towards dual-wavelength emission, required for applications such as Shifted Excitation Raman Difference Spectroscopy (SERDS).

Working principle

A rear-side anti-reflection coated diode laser is mounted on a micro-optical bench. Micro optics collimate rear and front facet emission. A reflecting volume Bragg grating is used as a wavelength-selective external cavity mirror to obtain laser emission. Depending on the application, the emission wavelength and its spectral width are both determined by the optical gain of the selected laser and the grating properties.

Current applications

  • Excitation light source for Raman spectroscopy and shifted excitation Raman difference spectroscopy in medicine and food quality control
  • Illumination for imaging and 3D modeling in traffic safety control

Typical wavelengths

  • 671 nm
  • 762 nm
  • 785 nm
  • 808 nm
  • 830 nm

Technology and packaging

  • Diode lasers with vertical layer structures realzed by MOVPE
  • Anti-reflection coating of laser facets
  • Active assembly of optical components on micro-optical bench
  • Characterization of electro-optical, spectral and special properties

Typical specifications

  • 1.5 W narrowband emission with spectral width of 100 pm achieved with broad area external cavity diode laser at 671 nm
  • 5 W peak power by external cavity tapered diode laser at 671 nm
  • Spectral emission width tailored for application by external grating (95% power content)
  • Reliable operation with lifetimes up to 14,500 hours
  • Compact footprint (max. 5 mm x 25 mm)

Funding has been provided by VDI/VDE Innovation + Technik GmbH for the BMBF-Project FreshScan (Duration: 01.07.2006 - 31.12.2009) and within the framework of EuroStars for the project CPILS (Duration 01.10.2017 - 29.02.2020).