LIQUID INSTRUMENTS Moku:Go Laser Lock Box User Manual
- June 11, 2024
- Liquid instruments
Table of Contents
Moku:Go Laser Lock Box
User Manual
Moku:Go Laser Lock Box
The Moku:Go Laser Lock Box enables you to stabilize a laser’s frequency to a
reference cavity or atomic transition using high-performance modulation
locking techniques. The Laser Lock Box is designed with the concept of staged
locking and a “Lock Assist”, enabling a user-defined locking process to
quickly lock to any zero-crossing on the demodulated error signal. It also
features an integrated two-channel Oscilloscope, allowing you to observe
signals at any point in the signal processing chain at up to 125 MSa/s.
Additionally, the built-in Data Logger enables long-term recording of signals.
Ensure Moku:Go is fully updated. For the latest information, visit:
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Introduction
Laser locking systems are used to control and match a laser’s frequency to an
optical frequency reference, such as an optical reference cavity or atomic
transition. Such systems are vital for high-resolution interferometric
measurements, spectroscopy, and time and frequency standards.
Locking a laser by forcing the laser and reference frequencies to be equal
allows for two scenarios:
- The locking system steers the laser frequency to be equal to the reference frequency, which is referred to as frequency stabilization; and
- The locking system forces the reference frequency to follow the laser frequency, which is referred to as frequency tracking.
Whether used for frequency stabilization or frequency tracking, the Moku:Go Laser Lock Box is designed to assist in laser locking systems. It offers compact setup, acquisition, and diagnostic features that makes it easier and quicker to set up and characterize laser locking systems.
User interface
The main user interface is divided into upper and lower screen sections. The upper user interface displays the processing chain and principal controls of the Laser Lock Box.
The lower half is readily set to display one of three parameter control panels: locking stages, Oscilloscope, and Data Logger.
| ID | Description |
|---|---|
| 1 | Locking stages |
| 2 | Oscilloscope |
| 3 | Data Logger |
Main menu
The main menu can be accessed by pressing the icon, allowing you to:
Upper user interface
| ID | Description | ID | Description |
|---|---|---|---|
| 1 | Main menu | 8b | Output limiter on slow PID chain |
| 2 | Input settings | 9a | Turn output 1 on/off |
| 3a-c | Tap to drop oscilloscope probe points to examine signals along the | ||
| processing chain | 9b | Turn output 2 on/off | |
| 4 | Tap to configure the digital filter | 10 | Configure scanning signal* |
| 5a | Tap to configure fast PID controller | 11 | Apply input offset |
| 5b | Tap to configure slow PID controller | 12 | Configure local oscillator |
| 6a | Connect fast PID chain to output | 13 | Configure the modulation signal* |
| 6b | Connect slow PID chain to output | 14 | Tap to choose the control panel |
| 7a | Apply output offset to fast PID chain | 15 | Control local oscillator |
frequency
7b| Apply output offset to slow PID chain| 16| Control local oscillator phase
8a| Output limiter on fast PID chain| |
Signal input
Tap the icon to configure the input settings for the signal input. Make
similar configurations on input 2.
Scan configurations
Tap the icon to configure the settings for the scan signal.
Modulation configuration
Tap the icon to configure the settings for the modulation signal.
Digital filter configuration
Immediately after the demodulator function, there is a digital filter designed
to remove unwanted signal components. This is highly configurable; just tap
the lowpass filter icon.
| ID | Description |
|---|---|
| 1 | Configure lowpass filter corner frequency: tap to enter frequency or touch |
and drag
2| Toggle between magnitude or phase plots
3| Tap to select filter shape
4| Fixed sample rate of 7.8125 MHz
5| Tap to select filter type
6| Tap to select filter order
7| Tap to enter corner frequency
Filter shapes
Select the shape of the filter by tapping the filter icon. There are two pre-
defined filter shapes and a fully customizable filter option.
PID controllers
The Moku:Go Laser Lock Box implements two cascaded PID controllers: a fast
controller and a slow controller. The input of the slow PID controller is the
output of the fast PID controller.
Both the fast and slow PID controllers can be configured graphically by
dragging interactively on the magnitude chart or by tapping on cross-over tabs
and entering frequency or gain on the soft keypad.
The PID controller provides full control over proportional, integral, and
derivative gain profiles with saturation levels available for the integral and
derivative components. The PID controller’s transfer function is updated in
real time.
| ID | Description |
|---|---|
| 1 | Drag or tap to enter integrator crossover frequency |
| 2 | Drag or tap to enter differentiator crossover frequency |
| 3 | Toggle between magnitude or phase plots |
| 4 | Drag or tap to enter integrator saturation |
| 5 | Drag or tap to enter proportional gain |
| 6 | Proportional, integrator, differentiator, double integrator (only on the |
fast controller), integrator saturation, and differentiator saturation
settings
7| Swipe to adjust selected PID parameter
Local oscillator
Configure the demodulation signal source in the settings dialog.
Demodulation
The demodulation mode determines which reference oscillator is used to
demodulate the input signal.
Modulation
The input signal can be demodulated with the modulation signal, which is user-
configured here. This local oscillator is locked to the modulation signal with
a frequency range from 1 mHz to 30 MHz.
Internal
The input signal can be demodulated with an internally generated reference
signal (independent from modulation signal). This local oscillator is derived
from the Moku:Go internal clock and thus shares the same time-based. The
frequency range of the internal reference is 1 mHz to 20 MHz.
External
The input signal can be demodulated by a direct external reference, permitting
the use of nonsinusoidal demodulation with the input signal applied on input
2.
External (PLL)
External (PLL) mode enables the Laser Lock Box to lock to an externally
sourced demodulation reference applied to input 2. This mode uses a digitally
implemented phase-locked loop (PLL) to track the phase of the external
reference with a user configurable bandwidth. To configure the bandwidth of
the PLL, tap the PLL icon to select the bandwidth between 1 Hz to 100 kHz. The
PLL will automatically lock to the strongest harmonic of the external
reference in the range of 10 Hz to 20 MHz with a manually configurable local
phase shift. The PLL can be manually set as low at 10 Hz. The PLL can be
frequency multiplied up to 250x or divided down to 1/8x with the Multiplier
for use as local oscillator, minimum Multiplier step size is 1/8 th. The
reacquire button can be used to relock to the external reference.
None
Bypass the demodulation step by selecting “None.” This enables modulation-free
locking techniques such as DC locking, fringe-side locking, and tilt locking.
Lower user interface
Use the lower user interface to either configure the locking stages or display
the half screen Oscilloscope or Data Logger.
Locking stage
| ID | Description |
|---|---|
| 1 | Lock stage 1 of (up to) 3 |
| 2 | Remove a certain action in the locking stage |
| 3 | Add a new locking stage (allows up to 3 stages at maximum) |
| 4 | Remove a certain locking stage |
| 5 | Engage the actions defined in the locking stage |
| 6 | Add a new action in the locking stage |
| 7 | Disengage the actions defined in the locking stage |
| 8 | Tap to connect the slow PID to Output 1 to enable the slow feedback |
| 9 | Tap to connect the fast PID to Output 2 to enable the fast feedback |
| 10 | Tap to enable/disable the scan signal |
| 11 | Tap to switch to the Oscilloscope to view the error signal, where the user |
can select the locking point
Add action
Choose any of the available actions to add to each locking stage. When
engaged, all of the actions associated with that stage will be enabled
simultaneously.
Oscilloscope
The Moku:Go Laser Lock Box includes a built-in Oscilloscope, enabling you to
observe and record data of up to two signals at a time in the Laser Lock Box’s
processing chain.
| ID | Description |
|---|---|
| 1 | Close Oscilloscope panel |
| 2 | Select Lock Assist |
| 3 | Share Oscilloscope data |
| 4 | Zoom in/out of the waveform |
| 5 | Reveal/hide settings sidebar |
| 6 | Tap to configure Oscilloscope settings, including Acquisition, Time base, |
Trigger, Type, and Sensitivity
7| Tap to select measurements tab
8| Tap to add time/voltage cursors, or drag right or drag up to create a
cursor
9| Pause/run Oscilloscope
The Oscilloscope will appear automatically when a probe point is activated.
You can hide the Oscilloscope by pressing the icon and reveal it by pressing
the icon.
Lock Assist feature
The Lock Assist can only be enabled after the locking stage is configured.
When the Lock Assist is enabled, the trigger settings will be configured to
synchronize the oscilloscope traces with the scan waveform. Selecting one of
the error signal’s zero crossings will then adjust the output offset to the
corresponding voltage and engage the first locking stage which is not already
fully engaged.
Additional details about the Oscilloscope can be found in the Moku:Go Oscilloscope manual.
Data Logger
The built-in Data Logger allows you to acquire data from up to four probe
points at a time at a maximum sampling rate of 500 kSa/s with 2 channels and 1
MSa/s with 1 channel. To access the data acquisition menu, press the icon.
More details about Data Logger are available in the Moku:Go Data Logger
manual.
| ID | Description |
|---|---|
| 1 | Upload saved data |
| 2 | Select the sampling rate at which your measurement is recorded |
| 3 | Select between Normal, Precision, or Peak Detection acquisition modes |
| 4 | Configure when to begin recording data |
| 5 | Configure measurement duration |
| 6 | Change filename and comments for the logged file |
| 7 | Record a new measurement |
The embedded Data Logger can stream over a network or save data on Moku:Go. For details, refer to the Data Logger user manual. More streaming information is in our API documents at apis.liquidinstruments.com
Additional tools
The Moku:Go app has two built-in file management tools: File Manager and File
Converter. The file manager allows users to download the saved data from
Moku:Go to a local computer, with optional file format conversion. The File
Converter converts the Moku:Go binary (.li) format on the local computer to
either .csv, .mat, or .npy format.
File Manager
Once a file is transferred to the local computer, a icon shows up next to the
file.
File Converter
The converted file is saved in the same folder as the original file.
The Liquid Instruments File Converter has the following menu options:
| Options | Shortcut | Description |
|---|
File
• Open file| Ctrl+O| Select a .li file to convert.
• Open folder| Ctrl+Shift+O| Select a folder to convert.
Exit| Close the file converter window.
Help
• Liquid Instruments website| Access the Liquid Instruments website.
• Report an issue| Report a bug to Liquid Instruments.
• About| Show app version, check update, or license information.
Power Supply
The Moku:Go Power Supply is available on M1 and M2 models. M1 features a
2-channel power supply, while M2 features a 4-channel power supply. The Power
Supply control window can be accessed in all instruments under the main menu.
The Power Supply operates in two modes: constant voltage (CV) or constant
current (CC) mode. For each channel, the user can set a current and voltage
limit for the output. Once a load is connected, the Power Supply operates
either at the set current or set voltage, whichever comes first. If the Power
Supply is voltage limited, it operates in the CV mode. If the Power Supply is
current limited, it operates in the CC mode.
| ID | Function | Description |
|---|---|---|
| 1 | Channel name | Identifies the power supply being controlled. |
| 2 | Channel range | Indicates the voltage/current range of the channel. |
| 3 | Set value | Click the blue numbers to set the voltage and current |
limit.
4| Readback numbers| Voltage and current readback from the power supply,
the actual voltage, and current being supplied to the external load.
5| Mode indicator| Indicates if the power supply is in CV (green) or CC
(red) mode.
6| On/Off Toggle| Click to turn the power supply on and off.
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Documents / Resources
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LIQUID INSTRUMENTS Moku:Go Laser Lock
Box
[pdf] User Manual
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