.. index::
   single: LIF Module
   single: LIF Module; experiment setup
   single: LIF Module; wizard page
   single: Laser-Induced Fluorescence
   single: REMPI
   single: Laser Scan
   single: Delay Axis; LIF
   single: Laser Axis; LIF
   single: Shots Per Point; LIF
   single: Randomize Delay Order
   single: Scan Order; LIF
   single: Auto Disable Flashlamp

.. _lif-experiment-setup:

LIF Experiment Setup
====================

When the LIF module is enabled in the Application Configuration (see
:ref:`application-config`), the first page of the
:doc:`Experiment Setup </user_guide/experiment_setup>` dialog gains an
**LIF** group alongside the **FTMW** group covered on the
:doc:`FTMW Experiment Setup </user_guide/experiment/acquisition_types>`
page. The LIF group defines the scan-axis parameters and options for
the laser scan; channel and gate configuration live separately in the
:doc:`configuration` (opened from **Hardware → LIF Configuration**),
where shots-per-point and digitizer settings are also configured.

.. image:: /_static/user_guide/lif-lif_exp_setup.png
   :align: center
   :alt: LIF group on the first page of the experiment wizard

The LIF group is divided into a scan-axes table that compares the
**Delay** and **Laser** columns side by side, and an **Options** panel
below it. The **LIF** checkbox at the top of the group enables or
disables LIF acquisition for this experiment; when unchecked, all
controls in the group are inactive and no LIF data are recorded.

Scan axes
---------

The scan-axes table holds four parameters for each axis:

- **Start** — the position at the first point.
- **Step** — the step size between consecutive points.
- **Points** — the number of points along the axis.
- **End** — the position at the last point, computed from
  ``Start + (Points - 1) * Step``. This row is read-only and updates
  as the other three values change.

The **Delay** column controls the timing axis (in microseconds) — the
time between the laser pulse and the detection gate, set on a
dedicated pulse-generator channel. The **Laser** column controls the
wavelength axis; the units displayed (here **nm**) are determined by
the connected laser hardware driver.

To perform a fixed-delay acquisition (scanning only the laser
frequency), set the Delay column's ``Points`` to 1 — the ``End`` row
tracks ``Start``. To perform a fixed-wavelength acquisition (scanning
only the delay), do the same on the Laser column. Both axes can be
active simultaneously; Blackchirp then steps through all combinations
of delay and laser positions, collecting the configured number of
shots at each combination. The shots-per-point value is set on the
:doc:`configuration`, not in the wizard.

Options
-------

The **Options** panel controls the order and behavior of the scan.

**Scan Order**
   Controls which axis is the outer loop during acquisition.

   - ``DelayFirst`` — the delay axis is the outer loop; for each delay value,
     Blackchirp steps through all laser positions before advancing to the next
     delay.
   - ``LaserFirst`` — the laser axis is the outer loop; for each laser
     position, Blackchirp steps through all delay values.

   Scan Order affects only the order in which points are visited; it does
   not change the on-disk data layout, which is always indexed by delay and
   laser axes independently. See :doc:`/user_guide/data_storage/lif` for the storage layout.

**Complete Mode**
   Controls what happens when all grid points have been acquired once.

   - ``StopWhenComplete`` — the acquisition ends after a single sweep through
     all points.
   - ``ContinueAveraging`` — the acquisition continues, co-averaging additional
     shots at each point indefinitely. Use this mode when higher signal-to-noise
     is needed; the experiment ends when the user clicks **Abort**.

**Auto Disable Flashlamp**
   When checked, the laser flashlamp is disabled when the acquisition
   ends, extending its firing lifetime.

**Randomize Delay Order**
   When checked, the delay points within each sweep are visited in
   randomized order rather than sequentially. Useful when the sample
   or background drifts slowly, since it decorrelates systematic drift
   from the delay coordinate. Only the delay ordering is randomized;
   the laser axis is always stepped sequentially.

Initializing from a previous experiment
---------------------------------------

When a past experiment is opened and the **Quick Experiment** option is used,
the LIF group is pre-populated with the scan parameters from that experiment.
All axis ranges, step sizes, and options are restored, providing a
convenient starting point for a repeat acquisition.