We utilize a Spectra-Physics table-top sized 650 mJ/pulse, 1064 nm (infrared) Nd:YAG laser that emits 10 ns pulses at 10 Hz repetition frequency.  This laser is also capable of operation at 532 nm via second harmonic generation in a frequency doubling crystal.  Changing the laser wavelength changes the target/radiation and vapor/radiation 

interactions, which changes the plasma temperature.  Higher spatial resolution is possible with the smaller diffraction-limited spot of the 532 nm laser, but scattered light at 532 is a larger concern.  Our spectrometer is not sensitive to the 1064 nm laser light, so we can operate arbitrarily close in time to the laser pulse.

 

Echelle Spectrometer

Our spectrometer is an ESA 2000 Echelle spectrometer from LLA Instruments, Inc.  This type of spectrometer utilizes an Echelle grating, which is optimized for maximum dispersion into very high diffraction orders (n=80-120).  This light is then cross-dispersed by a prism, resulting in a two dimension dispersion of the incident light. 

This 2-D “spectral map” is detected by an 1024 x 1024 pixel Intensified CCD-array.  (24 μm² pixel size). 

This allows us to obtain the entire spectrum (200-800 nm) with one laser shot with a .005 nm resolution.