Alan Stummer
Research Lab Technologist

Loch Box1

Warning:  This is a work in progress.  Take everything with a grain of salt!

I am curious who uses what. Are these webpages a waste of time, or are they any help to others?  Are the circuits, software and utilities appearing in other labs?  Please send your comments or suggestions or what you have used (or not) or schematics of your version or pictures or anything!  Email me, or be creative and send a postcard! I want to hear from the vacuum! Links

NOTICE: This webpage and associated files are provided for reference only. This is not a kit site!  It is a collection of my work here at the University of Toronto in the Physics department. If you are considering using any schematics, designs, or anything else from here then be warned that you had better know something of what you are about to do.  No design is guaranteed in any way, including workable schematic, board layout, HDL code, embedded software, user software, component selection, documentation, webpages, or anything.

All that said, if it says here it works then for me it worked. To make the project work may have involved undocumented additions, changes, deletions, tweaks, tunings, alterations, modifications, adjustments, waving of a wand while wearing a pointy black hat, appeals to electron deities and just plain doing whatever it takes to make the project work.


Started for Josiah Sinclair, Alex Bruening and Kent Fischer (postdoc) in Aephraim Steinberg's lab. Similar to Schlosser, this is an analog PID based laser wavelength controller. Although hopefully more versatile for unknown future uses, it is based on using the Qubig ADU (Advanced [laser] Driver Unit) which drives a 50MHz EOM, and a Thorlabs APD110A APD run in linear mode. The unit takes its feedback from the biploar demodulated baseline output from the ADU (called the IF output [sic]) which is the result of two lasers shone through a gas absorption cell. The unit's PID keeps one of the lasers at the proper wavelength with two outputs. A slow output (DC-50Hz) controls gross wavelength while a faster output (DC-50KHz, adjustable) proveds corrections in the audio range and minimal line narrowing. An offset control allows locking at various parts of any feature of the absorption spectrum, although nominally will be around zero. A scan mode with adjustable scan width allows sweeping either or both outputs to identify and zoom in any absorption feature.

The term "Error" means the unit's input, the differentiated absorption level, either the ADU (described above) or an amplified PD such as Thorlabs amplified detectors.

1The name Loch Box is a nod to the M Squared Laser's Glaswegian origins.

Operating Parameters
Error Input±200mVBaseline error signal
Error Input Bandwidth500Hz-100KHzAdjustable in 8 steps
Fast Output±10VInto high-Z
Fast Output BandwidthAs per APD input
Slow Output±10VInto high-Z
Slow Output Bandwidth50Hz
Internal Scan20Hz
Slow: ±25-1000MHz
Fast: ±0.067-2.7MHz*
p-p scan
External Scan Input±7V max
* Fast scan may be increased to ±40MHz max
Error InputError input
Fast OutputTo laser, fast piezo
Slow OutputTo laser, slow output
Scope X-axisDuring scan: frequency
During run: zero
Scope Y-axisPD monitor
Scan SourceSelect scan source int, off or ext
Fast OutputRun, off or scan
Slow OutputRun, off or scan
Error Input BWin KHz: 0.5, 1, 2, 5, 10, 20, 50, 100
Error Input Polarity+ve or -ve
Scan widthint or ext
Error Offset10-turn
Fast Output GainMaster gain
Slow Output GainMaster gain
Meter (with switch)
MeterSelectable for fast or slow output

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