8
ISOMET
3.
INSTALLATION AND ADJUSTMENT
The basic set-up below is described using the manual RF power limit adjustment.
The remote power adjustment is described from 3.15 onwards. The driver will default to
manual adjustment unless the remote power adjustment is selected,
3.1
Connect cooling water to the RFA741 at a minimum flow of 2.0 litres/minute at < 20 deg.C.
Refer to Figure 2. Use of a Corrosion inhibitor is strongly advised.
Connect cooling water to the AO device.
Due to the high RF power dissipated in the AO modulator, it is paramount that the device is
operated only when water cooling is circulating.
For optimum AO performance ensure the flow rate is more than 2 litres/minute at < 20 deg.C
3.2
With no DC power applied, connect the + 24V DC in to the screw terminals of the filtered
terminal. DO NOT APPLY POWER.
3.2
Connect the TNC output RF connector to the acousto-optic modulator TNC RF input.
(or a 50
Ω
RF load, if it is desired to measure the RF output power).
3.4
Connect the Interlock of the acousto-optic modulator (mini 3-pin snap connector) to the RF
driver “INT” input (mini 3-pin snap connector). Connect pin 1 to pin 1 and pin 2 to pin 2.
If the temperature of the modulator exceeds 32ºC or the internal driver temperature exceeds
50ºC then the interlock connection becomes open circuit, disabling the RF output. An LED
indicator illuminates when the Interlocks are closed and the RF is enabled. In addition, a open
drain ‘interlock valid’ signal output is provided on pin 2 of the D-type connector for remote
monitoring purposes.
3.5
Adjustment of the RF output power is best done with amplifier connected to the acousto-optic
modulator. When shipped, the Amplifier maximum output power is set to approx 100W
selecting the manual PWR ADJ pot and 120W for the digital pots.
The optimum RF power level required for the modulator to produce maximum first order
intensity depends on the laser wavelength and AOM aperture height. This value is called
“Psat”.
Applying RF power in excess of this optimum level will cause a decrease in first
order intensity, increase thermal dissipation and make accurate Bragg alignment
difficult.
It is therefore recommended that initial alignment be performed at a low RF power
level.
