A bias circuit sets the voltage of the current servo input to zero volts. The current servo input adds or subtracts current though 1 k Ω connected to the laser diode giving a modulation coefficient of 1 mA/V. If you are connecting other equipment to this input do not exceed 0.25 Vrms from a 50 Ω source or 1 mW of power. Note: a large voltage transient to this input could possibly cause damage to the laser diode. This input is normally connected to the RF output from the Laser Servo module, which applies FM sidebands at 4 MHz to the laser output. Over ~3 MHz the impedance of this input will approach the ac impedance of the laser diode of ~5 Ω. The RF input is ac coupled to the laser diode through a 10 nF capacitor. The Current Limit should be set below the maximum current for the laser diode. Set the selector knob to the I lim position and adjust the trimpot to the desired value.
The current limit set is a front panel trimpot adjustment. Then adjust the course current to the desired setting. To set the current, switch the selector knob in the monitor section so that the current LED (I) is lit. The course current control sets the laser diode injection current between 0 and 200 mA (0 and 500 mA for 500 mA version). Use this control for fine positioning of the laser frequency prior to locking. The fine current adjusts the diode injection current by ½-1 % of the coarse control setting. If the user attempts to set the current over the current limit setpoint the circuit shunts the excess current through a transistor to ground The current limit indicator lights when the current limit circuit is activated. When monitoring a Temperature Error, the output is 1V = 1☌. When monitoring a Temperature Setpoint, the output is 1mV = 1☌. When monitoring Current or Current limit, the output is 1V = 1 A and will include the current modulation/servo signal from the Servo Input connector.
The BNC monitor outputs a voltage corresponding to the monitor selection. When the switch is in the “ON” position, the current monitor accurately measures the current flowing through the laser diode. However, the Current Monitor will read up to 30 mA of current flowing through the short. NOTE: When the Laser Switch is in the “Off / Reset” position, the laser diode is shorted to ground and no current is flowing through the laser diode. Temperature coefficient 5) (controller, T2)Ĭalibrated to Analog Technologies ATH10KR8 Thermistor
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