Spectra-Physics Vanguard 355 nm UV laser
We have recently installed a Spectra-Physics Vanguard 355 nm 350 mW mode-locked solid state laser. This multistage solid state laser uses an infrared diode laser to pump a neodynium:YVO4 solid medium to produce a 1064 nm laser line, which is then frequency-tripled to 355 nm. While technically a pulsed laser, it operates at a sufficiently high frequency (in the MHz range) to function as a quasi-CW laser, as does our Lightwave Electronics 355 nm unit on the BD LSR II.
This laser takes the place of our water-cooled krypton-ion laser, which required a high voltage line and a chilled water source; the Vanguard is air-cooled and runs off normal 110V 20amp electrical service. This makes the laser less expensive to operate and more reliable. And no more chillers!
(Below). The Vanguard 355 nm laser installed in the second laser position on the FACSVantage DiVa (at left). The left-most portion on the unit is the lasing cavity, where the solid-state medium is pumped with a diode laser through a fiber optic (contained in the power supply/control module, at bottom right) to produce the 1064 nm laser line. The smaller module on the front of the laser is the frequency tripler, which generates the 355 nm output laser line. The iCyt Lyt-200C 488 nm laser is in the background, in the primary position.
(Below). Both lasers from the front of the sorter (Vanguard in the center). The OEM steering optics on the FACSVantage are retained to align both these lasers to the FACSVantage stream.
This laser has a power level permanently fixed at 350 mW. This relatively high power level is attenuated using UV-coated laser beamsplitters (CVI Laser) set at 45 degree angle in the path of the laser; these beamsplitters transmit a certain percentage of the laser light and reflect the remainder into a beam dump or a power meter for power monitoring. We use beam splitters coated for 50, 60 or 70% reflectance to produce attenuated laser power levels ranging from 85 to 150 mW.
(Below). The beamsplitter optic, mounting system and beam dump. The beamsplitter is mounted at a 45 degree angle directly in front of the laser, reflecting a portion of it and attenuating the beam. A solid aluminum plate protects against stray laser light outside the beam dump. The reflected portion of the beam is deflected into a beam dump, a hollow chamber with a non-reflective aluminum cone at its center. This units dissipates the unwanted portion of the laser beam and any generated heat. The beam dump can be replaced by a broadband power meter for monitoring laser emission.
(Below). Power monitoring system. The beam dump can be replaced with a broadband detector head, to monitor the power level of the reflected portion of the beam. A Coherent Smart Sensor computer interface links the detector head to a PC for constant monitoring of both power level and pointing stability.
This laser is useful the the same applications our previous water-cooled UV laser was used for, including Hoechst side population identification of stem cells and measurement of calcium flux using indo-1.
(Below). Alignment and sensitivity check for the Vanguard using Polyscience yellow-green microspheres (left and middle histograms, log and linear respectively) and a Molecular Probes InSpeck Blue microsphere array (right histogram).
(Below). Hoechst side population in mouse bone marrow on the FACSVantage DiVa with the Vanguard laser. Samples with no inhibition (left cytogram) and verapamil pre-treatment (right cytogram) are shown.
Data sheet for Vanguard 355 nm laser.
Vanguard test results on the FACSVantage DiVa
Power and pointing stability results here.