linien 0.0.18

Spectroscopy lock application using RedPitaya

Spectroscopy locking of lasers using RedPitaya (STEMlab 125-14) that just works. Linien aims to follow the UNIX philosophy of doing one thing very well. It is built with Python and Migen and is based on RED PID.

Features

• All inclusive: Modulation (up to 50 MHz), demodulation, filtering and servo implemented on the FPGA.

• Client-server architecture: Autonomous operation on RedPitaya. One or multiple GUI clients can connect to the server.

• Autolock: Click and drag over a line, and linien will automatically approach it and lock to it.

• Lock detection: linien is capable of detecting loss of lock.

• Automatic relocking: in that case, it can relock automatically using the autolock.

• Remote-controllable: The client libraries can be used to control or monitor the spectroscopy lock with python.

• Combined FMS+MTS: Supports dual-channel spectroscopy that can be used to implement combined FMS+MTS

• Logging: Use linien-influxdb to log the lock status to influxdb.

• TTL status: Outputs the lock status via TTL

Getting started

Linien runs on Windows and Linux. It is written for python 3 and can be installed using python’s package manager pip:

pip3 install linien

Run the application by calling

linien

If this doesn’t work, your local bin directory (e.g. ~/.local/bin) is probably missing in your PATH. Alternatively you can open linien using python:

from linien.client.client import run_application
run_application()

Then, you can enter your RedPitaya’s credentials and connect. If you agree, linien’s server component is automatically installed.

Physical setup

Scriptable interface

Linien running on RedPitaya can not only be controlled using the GUI but also by python scripts.

from linien.client.connection import BaseClient, MHz, Vpp
c = BaseClient(host, 18862, False)

# read out the modulation frequency
print(c.parameters.modulation_frequency.value / MHz)

# set modulation amplitude
c.parameters.modulation_amplitude.value = 1 * Vpp
# in the line above, we set a parameter. This is not written directly to the
# FPGA, though. In order to do this, we have to call write_data():
c.connection.root.write_data()

# plot control and error signal
import pickle
from matplotlib import pyplot as plt
plot_data = pickle.loads(c.parameters.to_plot.value)

# depending on the status (locked / unlocked), different signals are available
print(plot_data.keys())

# if unlocked, signal1 and signal2 contain the error signal of channel 1 and 2
# if the laser is locked, they contain error signal and control signal.
if c.parameters.locked.value:
    plt.plot(plot_data['control_signal'], label='control')
    plt.plot(plot_data['error_signal'], label='error')
else:
    plt.plot(plot_data['error_signal_1'], label='error 1')
    plt.plot(plot_data['error_signal_2'], label='error 2')

plt.legend()
plt.show()

For a full list of parameters that can be controlled or accessed have a look at parameters.py.

Development

As linien uses a git submodule, you should check it out like this:

git clone https://github.com/hermitdemschoenenleben/linien.git --recursive

To simplify development of the server component, its source code is automatically uploaded to the RedPitaya. For that, edit the VERSION file and replace it’s content with dev. Check that no server is running on the RedPitaya and start the client. Your development code should be uploaded to /linien and the linien server is started from that directory.

Fake server for testing the GUI:

python3 server/server.py --fake

Run server locally and control:

python3 server/server.py –remote-rp=root:[e-mail]

For this, acquisition_process.py has to be started on the RedPitaya.

In order to build the FPGA image, use scripts/build_gateware.sh.

See Also

• RedPID: the basis of linien