New UV Wavelengths Expand Multi-Parameter Capabilities
In both counting and sorting applications, researchers are looking to increase the informational content and level of detail by increasing the number of different parameters. Specifically, if the number of lasers wavelengths is increased, together with additional molecular or antigen-specific probes that are optimally excited at those wavelengths, then the number of parameters that can be analysed increases geometrically, because the fluorescence is subjected to multivariate analysis as a function of both excitation and fluorescence wavelength band. In this way, a “multi-colour” flow cytometer with five laser wavelengths and several wavelength-specific detectors can readily analyse 25 or more different parameters simultaneously, potentially elucidating even more sub-populations from a mix.
However, the entire visible spectrum is now well covered with smart plug and play laser wavelengths such as the OBIS series from Coherent. As a result, both instrument builders and laser manufacturers have identified that the only way to significantly increase the number of parameters is to extend the wavelength bandwidth – into the near-IR and more importantly into the ultraviolet.
In response to the need for new ultraviolet capability, Coherent recently introduced two additional OBIS laser wavelengths. These OBIS XT lasers feature 349 nm and 360 nm wavelengths with a choice of 20, 60, or 100 mW of output. They are diode-pumped solid-state (DPSS) lasers based on frequency-doubled praseodymium (Pr) technology. Previous attempts by the laser industry to commercialise this technology met with limited success, because Pr presents some unique laser challenges, particularly in the area of reliability.
However, Coherent engineers have developed proprietary solutions that now overcome these limitations. Moreover, these UV lasers are electrically efficient with a correspondingly low thermal load, and can thus be produced in a compact OBIS-style laser package that supports simple integration as discrete lasers, or alternatively in turnkey multi-wavelength OEM light engines – see figure 2.
Just as important, the lifetime and reliability is similar to existing OBIS laser wavelengths based on OPSLs and diode lasers, with the same industry-leading low noise characteristics. And like other OBIS lasers, they provide the same electronic interface and have the same output beam characteristics: the standard 0.7 mm TEM00 circular beam long used in flow cytometry, as well as identical specifications for beam pointing, beam circularity, etc.
In addition to flow cytometry, these new compact UV lasers are also expected to make their mark on other applications such as confocal microscopy and semiconductor inspection.
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