The nitrogen laser is experiencing new growth due to low cost and the MALDI technique.
Stanford Research Systems, Sunnyvale, California
The Matrix Assisted Laser Desorption and Ionization (MALDI) technique in 1987 led to a renewed interest for the nitrogen laser. MALDI allows large and fragile biomolecules to be desorbed and ionized intact, or with much less fragmentation. The technique increased the upper mass limit for mass spectrometric analyses of biomolecules to over 300,000 Da, and has enabled the analysis of large biomolecules by mass spectrometry to become easier and more sensitive.
Successful use of MALDI depends critically on using the right matrix, and for the matrices commonly used, an excitation wavelength of 337.1 nm is an excellent match. The 3- to 4-ns pulse width is also favorable for time-of-flight mass spectrometric (TOF-MS) analysis often used with MALDI. This, along with its low cost, has put the nitrogen laser back into the limelight.
The nitrogen laser, first demonstrated in 1963, was the subject of much interest in the 1970s and early 1980s because it produced nanosecond pulses of 337.1-nm ultraviolet light, a wavelength ideal for pumping dye lasers. Attractive features of the nitrogen laser were its relative simplicity, low cost, and the utilization of a ubiquitous and inexpensive gas for laser action. As solid-state laser technology advanced in the 1980s, interest in the nitrogen laser diminished, due in part to its low overall efficiency, making it a poor choice for applications requiring high laser energies. In addition, most nitrogen lasers involved flowing gas systems, which required bulky cylinders and monitoring of flow and pressure, a problem alleviated by solid-state lasers.
Stanford Research Systems has reduced or eliminated many of the concerns surrounding nitrogen lasers, including size, gas supplies, and safety. The NL100 is 3.75 × 3.75 × 11”, which is compatible with OEM design constraints. The laser includes all safety features required to meet the U.S. Federal CDRH 21 CFR 1040.10 regulations, and is completely self-contained, requiring no external gas cylinders or flow and pressure regulators. The plasma tube is sealed and the laser optics aligned in the factory using high-vacuum technologies. This laser produces 170-μJ pulses of 337.1-nm light in less than 3.5 ns, for a peak power of 45 kW. Pulses can be produced from an internal rate generator or from a user-supplied optoisolated TTL trigger. The repetition rate can be varied from 1 to 20 Hz from either the internal rate generator or the external trigger source. In addition, a sync-out is available as an option, where a TTL level pulse is produced that is synchronous with the laser pulse for experiments where precise timing is critical. The NL100 is suitable for a variety of pulsed UV applications, ranging from MALDI-TOF to fluorescence microscopy techniques.