Ring-down Box

You can measure the finesse of a resonator with the ring-down box without locking the resonator!

1. super fast (see characterization)
2. without locking the resonator

Use this formula to analyse the datapoints with \(x\): time, \(t\): delay time

\[y(x) = A \cdot e^{-\frac{x}{t}} + y_{0}\]

Afterwards calculate the finesse with \( F = 2 \pi \cdot t \cdot FSR\) with \(FSR\): free spectral range.

• max. Input PD-voltage: +5V or -5V
• Output TTL (Name: inv. Q): 5V
• Power voltage: +/-15 or +/-18V (max.)

• Switch A: unten = Eingang invertierend, oben = deaktiviert
• Switch B: unten = Ringdown Messung, oben = dauer-reset

• Electronic drawing: Electronic drawing_Ring_down_Box

• Inverter: LT1363
  • Invert negative input voltage to positive
  • Datasheet_LT1363
  • Power supply: +/-5V
• Comparator: AD8561
  • Compare input voltage and threshold value
  • Datasheet_AD8561
  • Power supply: +/-5V
  • High speed timing: 7ns @ 5V
• Flip-Flop: SN74HC74
  • Output of trigger
  • Datasheet_SN74HC74
  • Power supply: +5V
  • High speed timing: 15ns

• 1x XLR connector
• 1x Power supply +/-5V
• 1x single switch
• 1x double switch
• 3x BNC connctors
• 1x Potentiometer
• 1x big red button
• 2x 8-pin IC socket
• 1x 14-pin IC socket
• 3x PSK 3-pin cables
• 5x 100n capacitors
• some resistors (3x 100k, 1x 4.7k, …)
• 1x Al-box
• 2x PCBs

• Control of RF signal to the AOM
• Mixer typ: SRA-1+ (Datasheet_SRA-1+)
• 1x Resistor (100 Ohm)
• 2x diodes (type: 1N4748)
• 1x diode (type: Z3,9V)
• 3x BNC connectors
• 1x Al-Box

Rather build it like this:

Make sure that the input and output are as far apart as possible and the connections to the switch form a straight line. Otherwise the input line acts as an antenna and a part of the rf signal passes to the output if the switch is closed. For the same reason, try to make the wires within the box as short as possible.