Dual-wavelength diode laser for Raman spectroscopy

The FBH develops tailored diode laser and customized sensor systems for Shifted Excitation Raman Difference Spectroscopy (SERDS). This powerful and easy-to-use spectroscopic tool separates the wanted Raman signals from unwanted disturbing background interferences and brings Raman spectroscopy out of the lab, thus enabling real-world applications.

  • Scheme of a dual-wavelength diode laser for SERDS
    [+] Scheme of a dual-wavelength diode laser for shifted excitation Raman difference spectroscopy (SERDS)
  • Compact handheld probe for in situ Raman and SERDS investigations
    [+] Compact handheld probe for in situ Raman and SERDS investigations
  • Outdoor Raman and SERDS measurements using an in-house developed portable sensor system
    [+] Outdoor Raman and SERDS measurements using an in-house developed portable sensor system
  • Wavelength tuneable diode laser for Raman spectroscopy and SERDS
    [+] Wavelength tuneable diode laser at 488 nm for Raman spectroscopy and SERDS
  • Compact hybrid dual-wavelength diode laser for Raman spectroscopy and SERDS
    [+] Compact hybrid dual-wavelength diode laser at 671 nm for Raman spectroscopy and SERDS

Functional principle

An excitation light source with two individually controllable emission lines λ1 and λ2 is needed for SERDS. The spectral distance ΔλSERDS between both laser wavelengths should be close to the spectral width of the Raman signals under study, e.g. 10 cm-1.

A sample is excited with both laser lines successively. Only the Raman signals are shifted by the amount of the spectral distance ΔλSERDS, whereas disturbing background signals remain unchanged. After the measurement, both Raman spectra are subtracted and generate a SERDS spectrum. Here, SERDS separates the Raman signals from background signals such as fluorescence, ambient light, and others.

Applications

  • Laboratory and in situ investigation in application fields such as security, biology, medicine, food control, and pharmaceutical industry
  • Dual-wavelength diode laser applied for SERDS using confocal Raman microscopy

Typical wavelengths

  • 450 nm ... 1064 nm

Technology and packaging

  • Semiconductor structures with MOVPE
  • High-order surface DBR grating
  • Frequency conversion for VIS spectral range
  • Mounting of active (diode laser) and passive (micro-optics …) elements
  • Devices are realized on conduction cooled package (CCP) with its compact footprint
    (25 mm x 25 mm)

Typical data

Optical power:

  • Ridge-waveguide diode laser (RW)
    • ≤ 50 mW for 488 nm, 532 nm
    • ≤ 100 mW for 671 nm
    • ≤ 200 mW for 785 nm
  •  Broad area diode laser (BA)
    • ≤ 400 mW for 457 nm, 830 nm
    • ≤ 1.5 W for 671 nm, 785 nm
  •  Master oscillator power amplifier (MOPA)
    • ≤ 750 mW for 785 nm

Spectral width:

  • RW, MOPA
    • ≤ 1 cm-1
  • BA
    • ≤ 10 cm-1

Spectral distance for SERDS:

  • Preselection by internal or external wavelength stabilization
  • Adjustable, e.g. between 0 cm-1 and 32 cm-1, using dual-wavelength diode laser at 785 nm with implemented heater

Funding has been provided by the European Union’s Horizon 2020 research and innovation programme for the project MIB under grant agreement number No 667933 (duration 01.01.2016 - 31.12.2020), the research network Leibniz Health Technologies within the projects HypeRam (duration 01.06.2016 - 31.05.2019) and EXASENS (duration 01.12.2015 - 30.04.2019), and the BMBF's I4S (duration 01.07.2015 - 30.06.2018).