Chapter I

2.1.1. Ultraviolet lasers The ultraviolet laser systems used in the experiments described in Chapter 3 and listed in Table 3.1, covered a broad range of wavelengths and pulse durations. They included a seeded single-mode Nd:YAG laser, a nitrogen laser, and a Ti:sapphire ultrafast laser system. Nanosecond-duration pulses at 266 nm were generated using non-linear crystals to frequencyquadruple the single-mode Nd:YAG laser, while the output of the N2 laser at 337 nm was used directly. Femtosecond laser pulses were produced from a regeneratively amplified Ti:sapphire laser system that is described in more detail elsewhere [1]. The fundamental 120 fs, 800 nm output was frequency doubled (400 nm) or tripled (266 nm) in non-linear crystals. All of the lasers used except the seeded Nd:YAG have Gaussian spatial intensity profiles; the Nd:YAG has a “top hat” profile produced by a phase conjugating element. The beam profiles are somewhat altered by the 45° projection angle onto the sample. The mass spectrometer used at Vanderbilt is fitted with an optical port that will accept multiple lasers. A nitrogen laser (337i and 337-Si, Laser Science Inc., Franklin, MA) was often used to find appropriate voltage and timing settings, reducing the amount of valuable FEL time necessary for such tasks, as well as to compare the MALDI mass spectra generated by ultraviolet and infrared irradiation.