Diode Lasers & Controls

The laser light for this experiment is provided by seven 30 Watt, 795 nm solid-state diode lasers. The seven primary lasers used during the experiment are made by Coherent Semiconductor Inc. There will also be two diode lasers made by the Opto-Power Corporation that will be used as spares. Though there are some minor differences, both companies' laser systems perform the same function. Only the Ceherent lasers and control will be described here. If the Opto-Power lasers are used, readers are refered to the original version of the polarized $^3$He target OSP manual.

The diode lasers consist of a main enclosure which contains the diode, power supplies, fans and control systems for the laser. The laser light from the diode is sent into a flexible optical fiber which extends out of the main enclosure.The fiber is 5m long in a stainless steel jacket and is removable.

The lasers operate at diode temperature from $15^{\circ}$ C to $26.5^{\circ}$ C depending on the system. They are run at output power of 30 Watts which uses an operating current of 35-40 Amps. The output laser light has a central wavelength of 795 nm with a spectral width of less than 2 nm. The fiber diamter is 800 microns. The beam divergence is $< 0.20$ N.A.

The lasers have a local control system, which is integrated into the main enclosure. The local control allows adjustments in operating current (and therefore the laser power) and diode temperature (and therefore the wavelength within a small range).

During the experiment the lasers will be controlled remotely through EPICS. The lasers have a serial IO port on the back of the main enclosure which is connected to a VME RS-232 port. There is an MEDM GUI interface for each of the lasers, which allows remote control and monitoring of current and temperature as well as being able to turn each laser on and off.