.. index:: single: LIF Module; configuration single: LIF Channel single: Reference Channel; LIF single: Integration Gate; LIF single: Laser Power Normalization single: LIF Digitizer single: LIF Configuration single: Laser Control; LIF single: Flashlamp; LIF .. _lif-configuration: LIF Configuration ================= The **LIF Configuration** dialog collects the LIF digitizer settings, laser controls, and processing parameters that define an LIF measurement. The same controls surface in two places: - As the **LIF Configuration** page of the :doc:`Experiment Setup dialog `, where they are reviewed and validated before an experiment starts. This is the path most users take during routine acquisition. - As a standalone dialog opened from **Hardware → LIF Configuration**. Open it this way to tune the digitizer, run a live preview, or exercise the laser between experiments. Values set in one context are persisted and visible in the other. .. image:: /_static/user_guide/lif-lif_config.png :align: center :width: 800 :alt: LIF Configuration dialog The dialog is divided into three areas: - A **time-trace plot** spans the top. It displays the live digitizer waveform for the LIF channel (and the reference channel if enabled), with the current integrated value and the running average count shown in the top-right corner. Colored overlay regions mark the active integration gates so the gate positions can be verified visually. - The **LIF Digitizer** group occupies the bottom-left and holds the digitizer configuration, an **Averages** spin box, a **Reset** button, and the **Start Acquisition** / **Stop Acquisition** buttons that drive the live preview. - The bottom-right column stacks two groups: **Laser**, with manual laser position and flashlamp controls, and **Processing**, with the integration gates and optional smoothing filters. LIF channel and reference channel --------------------------------- The LIF digitizer records up to two analog channels. The role assignment is fixed and stated in the caption above the channel table: Channel 1 is the LIF signal and Channel 2, if enabled, is the reference. **LIF channel** (Ch 1) The primary signal channel. Blackchirp acquires this channel at every scan point and integrates its waveform over the LIF gate to produce the measurement value for that point. **Reference channel** (Ch 2) An optional channel used to record a signal proportional to the laser pulse energy (for example, from a photodiode or a pick-off power meter). The reference channel is disabled by default; enable it by checking the Ch 2 row in the **Analog Channels** table. When the reference channel is enabled, Blackchirp integrates both channels over their respective gates. The normalized LIF signal for each shot is:: signal_normalized = signal_lif / signal_ref Normalization is applied before co-averaging. If the reference gate integration returns a value of zero for a shot, that shot is not included in the normalized average to avoid division by zero. Digitizer settings ------------------ The **LIF Digitizer** group embeds the same widget the FTMW digitizer tab uses — an **Analog Channels** table on top with the **Data Transfer** and **Trigger** sub-tables below it. The Acquisition Setup group is omitted because LIF always acquires single records. For the field-by-field walkthrough, see :doc:`/user_guide/ftmw_configuration/digitizer_setup`. For per-device wiring, see :doc:`/user_guide/hw/lifdigitizer` and :doc:`/user_guide/hw/liflaser`. Below the digitizer fields, three controls drive the live preview: **Averages** Sets the number of waveforms co-averaged in the time-trace plot during a live preview. The same value is used as the **shots-per-point** target when the dialog is reached through the Experiment Setup dialog: each scan point in the resulting acquisition accumulates this many shots before advancing. **Reset** Discards the running average displayed in the time-trace plot, restarting the average from the next acquired waveform. Use this after changing acquisition parameters or after the laser has been retuned, to avoid contaminating the displayed average with shots taken under different conditions. **Start Acquisition / Stop Acquisition** Begin or end a live preview acquisition. Start Acquisition commits the current digitizer settings, locks them, and tells the LIF digitizer to begin streaming waveforms; the time-trace plot updates as shots arrive and the **Processing** group becomes active. Stop Acquisition halts the stream and re-enables digitizer editing. The same buttons drive the preview in both the standalone and Experiment Setup contexts; the preview does not record data to disk. Laser control ------------- The **Laser** group hosts the manual laser controls. The laser hardware driver determines the displayed units (e.g. nanometers, wavenumbers, or hertz) and the allowed range. **Position** Spin box for the laser setpoint. Edit the value, then click **Set** to send the new position to the laser. The spin box is disabled until the hardware reports the new position back, at which point the read-back value is loaded and the box is re-enabled. **Flashlamp** A checkable toggle button. The button reads **Enable** when the flashlamp is off and **Disable** when it is on; clicking it sends the change to the hardware and the button is briefly disabled until the hardware confirms. The Flashlamp control is omitted on lasers whose driver does not expose flashlamp gating. Disabling the flashlamp between acquisitions preserves its finite firing lifetime; see the **Auto Disable Flashlamp** option in :doc:`experiment_setup` for the automatic equivalent at the end of a scan. Manual tuning from this group is independent of any acquisition. It is the recommended way to verify laser tuning, exercise the flashlamp, or reposition the laser between experiments. Integration gates ----------------- Gates define the time window over which the digitizer waveform is integrated to produce a scalar measurement value at each scan point. The **Gates** sub-group inside Processing is a 2×2 grid: the rows **LIF** and **Reference** select the channel, and the **Start** and **End** columns hold the gate positions in **sample points** relative to the beginning of the digitizer record. The relationship between sample points and real time is: .. math:: t = \text{point} \times \Delta t where :math:`\Delta t` is the reciprocal of the digitizer sample rate. The integration is performed by summing the raw digitizer values within ``[start, end)``; each gate must span at least two points (End > Start), and Blackchirp nudges the other column automatically when an edit would violate that. The Reference row is editable only when the reference channel is enabled in the Analog Channels table. The reference gate does not need to coincide with the LIF gate; it should be positioned over the portion of the waveform that best represents the laser power for each shot. Hold **Ctrl** while clicking a spin box arrow (or pressing Up/Down) to adjust the gate position in steps of 10 sample points. .. note:: Gate positions are saved with the experiment and can be re-adjusted after the acquisition completes; the LIF tab re-integrates the stored waveforms with the new gates and updates the displayed plots. See :doc:`lif_tab` for the post-acquisition workflow. Processing filters ------------------ Two optional filters smooth each waveform before integration: **Low pass filter** First-order exponential filter, :math:`x_n = \alpha x_{n-1} + (1 - \alpha) x_n`. The **α** spin box sets the coefficient; setting α to 0 displays ``Disabled`` and bypasses the filter. **Savitzky-Golay smoothing** `Savitzky-Golay `__ smoothing. The group box is checkable — uncheck the title to bypass the filter. **Window** sets the (odd) window size and **Order** sets the polynomial order; Blackchirp clamps the order to ``Window − 1`` and snaps even window values down to the next odd value. The same filter controls appear on the LIF tab during and after acquisition; see :ref:`lif-tab` for the full per-control reference and the same-named **Reprocess All**, **Reset**, and **Save** buttons at the bottom of the Processing group. Those buttons are present in this dialog but inert — they activate only on the LIF tab after an acquisition has completed and there are stored waveforms to reprocess. In this dialog the filters affect only the live preview trace; their values are persisted along with the gate positions and applied at the start of the next acquisition. The Processing group is disabled until **Start Acquisition** has been clicked, since the filters operate on a known record length.