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| === Changes in the configuration of the photodiodes === For the 40m Upgrade there will be changes in the configuration of the photodiodes. Chnges in the configuration of the photodiodes will mostly dictated by: 1) the adoption of different modulation sibands than the current ones; 2) the introduction of 3f locking techniques; 3) the use of an additional green laser beam. |
== A New RF System For the Upgrade == The Upgraded 40 Meter will have an entirely new configuration of the RF system. That is mostly because of two fundamental reasons: 1. the length of the short cavities will change (getting longer); 2. the interferometer will be set in a [[broadband sensing configuration]] and [[a new locking scheme]] and signals will be necessary. |
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| A different configuration of the demodulator will also be necessary fo the new RF signals. | === Main Features of the new RF Scheme === |
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| The following diagrams and tables summarize which changes will have to happen. | The change of the length of the recycling cavities will impose different sideband frequencies. The frequency f1 of the first sideband will be now about 11 MHz, ad the second one will be 5xf1=55 MHz. The modulations will be generated by a [single broadband EOM], thus abandoning the current two parallel EOMs contained in the Mach-Zehnder interferometer on the PSL Optics Table. Also there will be a single main oscillator to generate the main 11 MHz frequency. All the other signals, with frequencies multiple of the main one, 2x, 3x, 5x, 10x, 15x respectively, will be generated starting from it, rather than by independent oscillators. f1 will be generated by a crystal oscillator; f2 will be obtained by f1 by means of a 5-time frequency multiplier. The two modulations will then be combined into a single signal that will drive the EOM. The plan under study also uses the same signal from the main oscillator for the demodulation of the signals from the RF photodiodes. A diagram representing the configuration of the new RF system is shown in the following picture. ==== Tables and diagrams ==== |
A New RF System For the Upgrade
The Upgraded 40 Meter will have an entirely new configuration of the RF system. That is mostly because of two fundamental reasons:
- the length of the short cavities will change (getting longer);
the interferometer will be set in a broadband sensing configuration and a new locking scheme and signals will be necessary.
Main Features of the new RF Scheme
The change of the length of the recycling cavities will impose different sideband frequencies. The frequency f1 of the first sideband will be now about 11 MHz, ad the second one will be 5xf1=55 MHz.
The modulations will be generated by a [single broadband EOM], thus abandoning the current two parallel EOMs contained in the Mach-Zehnder interferometer on the PSL Optics Table.
Also there will be a single main oscillator to generate the main 11 MHz frequency. All the other signals, with frequencies multiple of the main one, 2x, 3x, 5x, 10x, 15x respectively, will be generated starting from it, rather than by independent oscillators.
f1 will be generated by a crystal oscillator; f2 will be obtained by f1 by means of a 5-time frequency multiplier. The two modulations will then be combined into a single signal that will drive the EOM.
The plan under study also uses the same signal from the main oscillator for the demodulation of the signals from the RF photodiodes.
A diagram representing the configuration of the new RF system is shown in the following picture.
Tables and diagrams
[attachment:40mUpgrade_PDlists.pdf Table of old and new PDs plus diagram of signal extraction scheme]
[attachment:40mPDs.pdf Table of PDs and Demodulators]