UniHarp

The Histogram measurement class builds a distribution of photon arrival times relative to a reference signal, typically the sync signal of a pulsed excitation source. Each photon event is assigned to a time bin based on its arrival delay after the sync pulse.

The resulting histogram represents the temporal distribution of photon arrivals, commonly used in time-correlated single photon counting (TCSPC) experiments such as time-resolved photolumindescence (TRPL). It provides information such as fluorescence lifetimes or decay dynamics.

The Time Trace measurement class calculates the photon count rate as a function of time. Photon detection events are grouped into consecutive time bins of fixed duration. The number of photons detected within each bin is counted, producing a time-dependent trace of photon intensity.

This measurement is typically used to monitor temporal fluctuations in photon emission, such as blinking behavior of single emitters, fluorescence intensity changes, or detector stability over time.

The Correlation measurement class computes the temporal correlation between photon detection events. It evaluates the time differences between photons detected on one or more channels and accumulates them into correlation bins.

Depending on the analysis type, different algorithms are used. For example, g² correlations are typically computed using bins of constant width, whereas fluorescence correlation spectroscopy (FCS) calculations often employ a multi-tau algorithm, where bin widths increase pseudo-logarithmically to efficiently cover a wide range of time scales.

The resulting correlation function describes how likely photon events are to occur at a certain delay relative to one another. This allows the investigation of photon statistics and dynamic processes in the sample. Typical applications include photon antibunching measurements, FCS, and cross-correlation between detection channels.

The Unfold and Raw measurement classes provide direct access to time-tagged photon events. Unfold outputs individual detection events with their timestamps and channel information in a structured table format, enabling detailed inspection and custom analysis of photon sequences. Raw mode records the unprocessed TTTR data stream directly to a PTU file without intermediate processing or visualization, ensuring maximum recording performance and efficient storage for large datasets intended for offline analysis.

The “Coincidence” manipulator identifies photon events that occur within a defined time window across multiple input channels. When events from the selected channels are detected within this temporal window, they are considered a coincidence and can be written to a dedicated software channel or replace the original events. The manipulator also allows different coincidence counting modes and timestamp definitions, enabling flexible control over how coincident events are generated and represented in the data stream.

A common application is the detection of simultaneous photon events in multi-detector experiments. For example, in a two-detector photon correlation measurement, the coincidence manipulator can identify photon pairs detected within a few nanoseconds, allowing further analysis of photon statistics or quantum correlations.

The “Herald” manipulator filters photon events based on the detection of a herald photon on a specific input channel. For each photon event on selected gate channels, the manipulator opens a time gate after a configurable delay and checks whether a herald photon occurs within this gate interval. Depending on the configuration, events associated with herald detections can either be accepted or rejected, and the resulting events may be written to new software channels or overwrite the original ones.

This mechanism is commonly used in heralded photon experiments such as spontaneous parametric down conversion (SPDC), where the detection of one photon indicates the presence of another correlated photon. By filtering events based on the herald signal, the manipulator can significantly reduce background events and isolate the photon pairs of interest.

The “Merge” manipulator combines photon events from multiple input channels into a single software channel. When an event from one of the selected channels is detected, its channel identifier is replaced with the new merged channel while the timestamp remains unchanged. Events from channels that are not part of the configuration pass through the manipulator unaffected.

This functionality is useful when signals from several detectors should be treated as a single logical source. For example, events from multiple detectors monitoring the same optical path can be merged into one channel to simplify subsequent coincidence or correlation analysis.

The “Delay” manipulator shifts the timestamps of photon events from a selected channel by a fixed time offset. The configured delay is added to the timestamp of each event on that channel, while all other channels pass through unchanged. This allows precise correction of timing differences introduced by detectors, cables, or electronic components in the measurement setup.

An example application is the temporal alignment of signals from multiple detectors. If one detector introduces an additional delay due to longer cable paths or internal processing, the delay manipulator can compensate for this offset to ensure accurate coincidence or correlation measurements.

The “Sub-Stream” manipulator filters the photon event stream based on a defined time interval. Only events whose timestamps fall between a specified start and stop time are passed through the manipulator, while all other events are discarded. This filtering is applied to all channels simultaneously without modifying the original channel assignments.

This manipulator is useful when analyzing only a specific portion of a measurement. For instance, it can be used to isolate a region of interest within a long acquisition, such as a time window where a sample was actively excited or when a particular experimental condition was applied.