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Home > Applications Blog > Technical Tips > Tech Tip: Choosing Raman Excitation Wavelengths

Tech Tip: Choosing Raman Excitation Wavelengths

Raman spectroscopy offers a number of benefits for testing and characterization, with the selection of system components and measurement parameters offering great flexibility. In this technical tip, we’ll focus on the choice of Raman laser excitation wavelength.

High Resolution 532 nm Laser Spectrum

High Resolution 532 nm Laser Spectrum

532_laser_fatboyRaman signal is proportional to 1/λ4 of the excitation wavelength. While this makes it tempting to use a short wavelength laser, autofluorescence generated in the sample can easily degrade signal to noise and make Raman peaks difficult to resolve. Organic samples are particularly prone to autofluorescence, driving excitation to red or NIR wavelengths (660-830 nm). The effect is much less pronounced for inorganic materials, including carbon nanotubes and fullerenes, more commonly studied with 532 nm laser excitation.

Excitation at 1064 nm virtually eliminates autofluorescence, but also reduces the Raman signal significantly, further complicated by the reduced sensitivity of NIR spectrometers. UV excitation is also tempting, as the full Raman fingerprint region can be collected prior to the onset of autofluorescence at ~330 nm, but again technical limitations prevail – UV lasers and filters are more expensive and lower performance, while the high energy of UV light can damage samples quickly during measurement.

Raman Excitation Laser Options from Ocean Optics

Laser ModuleRaman spectroscopy requires laser sources with spectral purity and wavelength stability. Our Raman lasers use an innovative stabilization technology that provides extremely narrow wavelengths that remain locked at the desired excitation wavelength regardless of ambient temperature changes. These high-power excitation sources combine integrated laser drivers and thermoelectric coolers in a compact footprint. Lasers are available for various excitation wavelengths and can be used as turnkey (with built-in laser drivers and thermoelectric cooling) or integrated (designed for use in OEM systems) laser packages.

 

Turnkey Laser Options

Item Excitation Wavelength Output Power Connector
LASER-532-IP-LAB 532 nm >50 mW FC
LASER-532-IP-LAB-S 532 nm >50 mW SMA 905
LASER-785-IP-LAB 785 nm >350 mW FC
LASER-785-IP-LAB-S 785 nm >350 mW SMA 905
LASER-785-LAB-ADJ 785 nm Adjustable to >350 mW FC
LASER-785-LAB-ADJ-S 785 nm Adjustable to >350 mW SMA 905

Integrated Laser Options

Item Excitation Wavelength Output Power Connector
LASER-532-IP-LAB-OEM 532 nm >50 mW FC
LASER-532-IP-LAB-OEM-S 532 nm >50 mW SMA 905
LASER-785-IP-LAB-OEM 785 nm >350 mW FC
LASER-785-IP-LAB-OEM-S 785 nm >350 mW SMA 905

Additional excitation wavelengths and other options are also available. Please contact an Applications Scientist for details.