SPSA FROG

In situations where laser pulse-amplitude and -phase variations occur faster than available detectors can measure, Frequency-Resolved Optical Gating (FROG) uses optical nonlinearities to mix a laser pulse signal with a modified replica of itself. The resulting signal is then spectrally-resolved. By recording the spectrum at each delay, FROG gathers enough information about the pulse to retrieve the pulse signal's amplitude and phase with a few, known, ambiguities.

Traditionally, FROG uses a generalized projection-based algorithm to retrieve the amplitude and phase. Here, we experiment with replacing that algorithm with Simultaneous Perturbation Stocastic Approximation (SPSA). SPSA has strong theoretical foundations and is very simple to implement.

Using SPSA FROG

Disclaimer: SPSA FROG is still very experimental and needs to be tuned.

git clone https://github.com/leroix/haskell-spsa-frog

The first time through, you need to download and install a ton of dependencies, so hang in there.

cd haskell-spsa-frog
cabal-dev install \
    --enable-tests \
    --only-dependencies \
    --flags=developer
    -j

The cabal-dev command is just a sandboxing wrapper around the cabal command. The -j flag above tells cabal to use all of your CPUs, so even the initial build shouldn't take more than a few minutes.

cabal-dev configure --enable-tests --enable-benchmarks --flags=developer
cabal-dev build

Refer to the tests to see how the functions in Math.FROG.Retrieval are used. It will be helpful to understand the haskell-SPSA module.

Running Tests

Once you've built the code, you can run the entire test suite in a few seconds.

dist/build/tests/tests +RTS -N

We use the direct executable rather than cabal-dev tests because it doesn't pass through options very well. The +RTS -N above tells GHC's runtime system to use all available cores. If you want to explore, the tests program (dist/build/tests/tests) accepts a --help option. Try it out.

Tests From GHCI

You can run all the tests from ghci.

cabal-dev ghci

starts up the REPL.

> import Test.Test
> runAllTests

Or you can run a single test

> runTest "Gaussian" -- follows test patterns in Test.Framework
> runGroup "Retrieval" -- if you want to run all tests in the "Retrieval" group

Why Haskell?

http://www.haskell.org/haskellwiki/Why_Haskell_matters