Wavelength Stabilized Diode Laser for Raman Spectroscopy

Raman spectroscopy is a suitable tool for both qualitative and quantitative analysis of chemicals. However, this technique has partically been limited from wider use because of its high cost factor, particularly in its excitation source. B&W TEK has recently developed a series of narrow linewidth diode lasers called CLEANLAZE. These lasers offer high performance and are affordably-priced, and thus pave way to low-cost Raman spectroscopy applications.

CLEANLAZE Laser vs. External Cavity Laser

The CLEANLAZE laser includes a high-power broad-stripe laser diode. With the help of an innovative cavity technology, the output spectrum of this laser diode is narrowed and stabilized. Traditional external cavity lasers are not only delicate but also involve high maintenance cost because of the addition of external reflective dispersive elements that result in a long cavity length.

However, in case of the CLEANLAZE laser, the wavelength selective element forms an integral part of the laser diode via hybrid integration process. Therefore, the laser is compact and remains stable to environmental changes such as humidity variation, temperature, and vibration.

The use of broad-stripe laser diode ensures the low cost of the entire module, while providing much higher output power of up to 1.5W when compared to DBR and DFB lasers.

The broad-stripe laser contains unwanted spectral sidelobes that are filtered out by the wavelength selective element. This wavelength selective element locks its output wavelength to the central wavelength of the filter. With the combination of unique cavity technology and improved proprietary manufacturing process, the laser’s spectral linewidth can reach 0.05nm at 785nm, while the temperature sensitivity of the central wavelength can reach down to 0.01m/°C.

Such low temperature sensitivity makes it possible for Raman excitation sans using a thermal electric cooler and consumes less power for portable Raman instrumentation. The laser also includes features such as -35°C to 50°C operating temperature range, fiber coupled output, and an extended life time of >10,000 h.

Experiment and Results

(a) Comparison of the output spectrum of a regular broadstripe diode laser and a CLEANLAZE diode laser; (b) Comparison of Raman spectrum of a Tylenol sample excited with the regular broad-stripe diode laser and the CLEANLAZE diode laser.

Figure 1. (a) Comparison of the output spectrum of a regular broadstripe diode laser and a CLEANLAZE diode laser; (b) Comparison of Raman spectrum of a Tylenol sample excited with the regular broad-stripe diode laser and the CLEANLAZE diode laser.

Figure 1 shows an example of the high performance of the CLEANLAZE laser, wherein the output spectrum of a CLEANLAZE laser and a standard broad-stripe diode laser are compared with the Raman spectrum of a Tylenol sample excited by the two lasers. It can be clearly seen that the Raman spectrum generated by CLEANLAZE laser offers much higher resolution.

Conclusion

B&W Tek‘s CLEANLAZE diode lasers provide a high performance yet low-cost solution to high resolution Raman spectroscopy applications and make it possible to use this technique on a wider scale.

This information has been sourced, reviewed and adapted from materials provided by B&W Tek.

For more information on this source, please visit B&W Tek.

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