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ISOMET RFA741 Series Instruction Manual

Acousto-optic modulator driver
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Jan 18
Acousto-Optic Modulator Driver
Including: Modulator Alignment
AOM740-H
Instruction Manual
RFA741 Series
Digital Modulation, Dual Frequency
Remote Power Level Control
Models -
RFA741
Options –xxx, combinations possible.
- BR
ISOMET (UK) Ltd, 18 Llantarnam Park, Cwmbran, Torfaen, NP44 3AX, UK.
Tel: +44 1633-872721, Fax: +44 1633 874678, e-mail:
: 40MHz / 50.7MHz, 180W output
: Brass water cooled heatsink
ISOMET CORP, 5263 Port Royal Rd, Springfield, VA 22151, USA.
Tel: (703) 321 8301, Fax: (703) 321 8546, e-mail:
www.ISOMET.com
ISOMET
isomet@isomet.com
isomet@isomet.co.uk

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Summary of Contents for ISOMET RFA741 Series

  • Page 1 ISOMET CORP, 5263 Port Royal Rd, Springfield, VA 22151, USA. Tel: (703) 321 8301, Fax: (703) 321 8546, e-mail: isomet@isomet.com www.ISOMET.com ISOMET (UK) Ltd, 18 Llantarnam Park, Cwmbran, Torfaen, NP44 3AX, UK. Tel: +44 1633-872721, Fax: +44 1633 874678, e-mail: isomet@isomet.co.uk...
  • Page 2 ISOMET GENERAL Key Features: • 24Vdc, water cooled high power amplifier • RF output >150W at 40.00MHz, and >150W at 50.67MHz • RF rise/fall time < 400/100nsec at 150W • High Speed Digital ON:OFF modulation • Modulation ON level is defined by two methods for each frequency - Digitally programmed potentiometer stack - Manual adjustment potentiometer.
  • Page 3 ISOMET CONTROL Two inputs directly control the RF output; Gate and Freq Modulation. The Gate response time (tgm, fig1) is approximately 1msec The RF Frequency Modulation response time is < 50nsec The relationship between the driver control inputs, the RF waveform and AO response is shown below.
  • Page 4 ISOMET Gate (active high enables the RF amplifier) PLC compatible opto-isolated input Default condition is RF Off. A high level (5V < V < 24V) will gate the RF ON. A low level (0V < V < 4V), or not connected will gate the RF OFF.
  • Page 5 ISOMET Thermal Interlocks The AOM and Driver are fitted with thermostatic switches which will switch open circuit if a predetermined temperature is exceeded. These thermal interlocks will reset once the AO device and / or RF driver are cooled below this temperature.
  • Page 6 ISOMET LED Indicator and Monitor outputs The front panel tri-colour LED indicates the operating state. (RF PWR ADJ) 51MHz 40MHz The top LED will illuminate RED when there is a poor VSWR load (High reflected RF power fault). Normal condition is OFF A fault signal is triggered when the reflected RF power exceeds approximately 50% of the average forward power for more than 1 second.
  • Page 7 ISOMET LEDS Off The GREEN and/or YELLOW LED’s will not illuminate if : a) the internal driver thermal interlock switch is open (Over temperature fault) b) the AOM thermal interlocks switch is open (Over temperature fault) c) the AOM thermal interlock is not connected to the driver interlock input d) the DC supply is off.

  • Page 8: Installation And Adjustment

    ISOMET 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, Connect cooling water to the RFA741 at a minimum flow of 2.0 litres/minute at <...
  • Page 9 ISOMET A typical relationship between RF drive and efficiency for a correctly aligned AOM740-H at 10.6um is illustrated below. 100% 90 100 110 120 130 140 150 160 RF Pow er (W) Locate the PWR ADJ access holes on the driver end plate.
  • Page 10 ISOMET Input the laser beam toward the centre of either aperture of the AOM. Ensure the polarization is horizontal with respect to the base and the beam height does not exceed the active aperture height of the AOM. Start with the laser beam normal to the input optical face of the AOM and very slowly rotate the AOM (either direction).
  • Page 11 ISOMET The slave address for the digital I2C potentiometer is at 0101100. (AD0 = AD1 = 0) Maximum resistance equates to maximum RF power. The digital potentiometer value is non-volatile and will recall the last saved value on power- Control...
  • Page 12 ISOMET The four digital pots are configured into a potential divider. The main power control pots W1 and W2 are in parallel and equate to 5Kohm resistance. The upper and lower limit adjustment Pots W3 and W0 apply to both 40MHz and 50MHz powers.
  • Page 13 ISOMET The full range power adjustment is shown below. Settings: RDAC3 = 0 (R_W3=0k) and RDAC0 = 255 (R_W0=0k). The V_Control scale equates to 0 – 255 adjustment range on RDAC1 (W1) or RDAC2 (W2) Digital Pot RF Control V_Control (Volts) By adjusting the values of RDAC0 and RDAC3 it is possible to increase the adjustment resolution of the 8-bit power level control at 40.0 MHz (RDAC1) and 50.7MHz.(RDAC2) over a defined range.

  • Page 14: Maintenance

    ISOMET MAINTENANCE Cleaning It is of utmost importance that the optical apertures of the deflector optical head be kept clean and free of contamination. When the device is not in use, the apertures may be protected by a covering of masking tape.
  • Page 15 ISOMET RFA741 Connection Summary 15 way ‘D’ Type Control Connection Signal (see notes) Type Pin out connection NECESSARY Digital Gate (slow)** Input Signal pin 8 PLC high (5v<V<24v) = ON Return pin 15 PLC low (0.0v<V<4v) or NC = OFF...
  • Page 16 ISOMET Modulation and Gate Input connections J1 = GATE input RF Driver D-Type PLC compatible Logic HIGH (5V < V < 24V) = ON 15way Logic LOW (0V < V < 4V) = OFF J2 = FREQ MOD input TTL compatible Logic HIGH (3V <...
  • Page 17 ISOMET +24Vdc GATE Input +Vcc +Vset Output Oscillator +Vcc PA Transistor Mixer Pre-Amp Select Oscillator FREQ Modulation Input 4 Channel Digital Pot Select S0 = 1 = Dig Pot S0 = 0 = Man Adj Figure 3: Driver Block Diagram...
  • Page 18 Normally Closed Contacts : Pins 1 , 2 Not connected : Pin 3 Either optical face can be used for input. Thus with reference to the above diagram, the input laser beam can also be from the right to left. Figure 4: Typical Configurations using RFA741 series.
  • Page 19 ISOMET Basic AO Modulator Parameters Intensity Modulation Driver Input Laser Beam θ θ BRAGG 1st Order Deflected Beam 0th Order The input Bragg angle, relative to a normal to the optical surface and in the plane of deflection is: θ...