| New Focus low power scannable single-mode laser is at top center of photo. SDL laser amplifier is at center foreground. |
Laser Development
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Diode lasers are being developed at UC Irvine for laser induced fluorescence (LIF) experiments. We have been working with two companies, SDL, Inc. and New Focus, Inc. SDL now sells a laser we use for argon ion plasma LIF in the red wavelength range of 664 - 668 nm with an output power up to 0.5 W cw. The minimum power required by pumped dye laser schemes for many plasma LIF experiments is typically about 40 mW, with more being desirable for certain applications. 500 mW maximum power allows considerable flexibility in experiment signal-to-noise design issues. New Focus is developing series of low power tunable, single mode diode lasers with powers up to 8 mW. Again, our interest is for LIF. |
After three generations of laboratory experiments on the
668 nm 0.5 W laser we have a long-term reliable laser from SDL. The first two generations
showed proof of principle; that it was possible to fluoresce argon with a solid state
laser at 664 and 668 nm. The lifetimes of the laser diode chip were small however, only
about 40 hours each. The third generation experiments now provide routine argon ion
distribution functions and some time-resolved data. The third generation experiment has
had the chip on for over 400 hours, with SDL's expectations of about a 4000 hour lifetime.
The SDL laser is available commercially (SDL's TC Series) at a price of about $18,500 for
the laser. Laser controllers are available from a number of vendors such as the Newport
Corporation 8000 series, SDL 824, etc.
The SDL laser can be run with its cavity in place, providing a diffraction grating for
tuning purposes. Using this method, it can be tuned to argon LIF in the broadband tagging
approach. The laser can be manipulated to run in one or two modes (cavity issues give
small-mode spacing about 1.79 GHz apart and large-mode spacing around 15-25 GHz apart).
With the laser tuned by the cavity, temperature control of the laser diode chip can cause
the mode to be swept across the Doppler-broadened ion distribution. Our experiments
required a scan of 100 mK to get a full ion distribution. Alternatively, an ion
distribution can be obtained by mounting a PZT on the diffraction grating. The PZT
technique we have tried works but has a small sinusoidal contribution superimposed on the
distribution, perhaps due to PZT spatial oscillations during driving.
The configuration shown above has the SDL laser driven by the New Focus 6308 5 mW single
mode laser tunable over 10 nm. The New Focus laser beam is injected into the back end of
the SDL (hole drilled in case) with the SDL diffraction grating/cavity removed. The 5 mW
beam enters the diode chip and is amplified up to a factor of 100 in power. This is called
a master oscillator power amplifier (MOPA) configuration. In the MOPA arrangement the SDL
laser diode chip acts just as an amplifier. It may be set for constant power output. The
laser frequency is determined by the New Focus source, lasing in a single mode which can
be scanned by a PZT over the many GHz of the plasma ion distribution. The New Focus 6308
is available now in two configurations at about $12 and $18k.
Most recently, New Focus has built us a low power tunable single mode laser which scans only over 100 GHz. This new laser is their Vortex laser (model number 6009). By limiting the scanning capability New Focus has brought the Vortex to market at about $8k.
With this New Focus Vortex laser available for purchase,
the entire tunable diode laser scheme would consist of one low power tunable diode laser
from New Focus, one laser amplifier from SDL, and a controller for the amplifier.
Capability provides 0.5 W tunable over the Doppler-spread argon ion lines. Total cost is
be about $33k plus tax and shipping. Alternatively, SDL has a preliminary product offering
of the MOPA configuration in one case (SDL-TC40).
Further information about the operation of these lasers in the various configurations is
at Lab
Publications, our recent Presentations or questions may be e-mailed to mcw@uci.edu.