Wavelength Scan Measurements

Warning

These measurement commands are under construction. The interface and behavior may change in future releases. Please report any issues or suggestions.

This page documents the automated wavelength scan measurement commands available in PANDORA. These commands coordinate the monochromator, electrometers, shutter, and other subsystems to perform systematic measurements across a wavelength range.

Overview

PANDORA provides several wavelength scan commands for different measurement scenarios:

Wavelength Scan Commands

Command

Description

measure-pandora-throughput

Basic throughput measurement (current mode)

measure-pandora-throughput-beta

Enhanced throughput with dark measurements

measure-pandora-tput-final

Production-ready scan with overflow handling

measure-pandora-charge

Charge accumulation measurement (coulomb mode)

Throughput Measurements

The throughput commands measure the ratio of main beam flux to monitor diode flux across wavelengths using current mode on the Keysight electrometers.

Basic Throughput Scan

Note

This command is under construction and may have limited functionality.

pb measure-pandora-throughput <exptime> <lambda0> <lambdaEnd> [options]

Arguments:

  • exptime: Exposure time per measurement point (seconds)

  • lambda0: Start wavelength (nm)

  • lambdaEnd: End wavelength (nm)

Options:

  • --step <nm>: Wavelength step size (default: 1 nm)

  • --ndFilter <name>: ND filter to use (ND05, ND10, ND15, ND20, CLEAR)

  • --nrepeats <n>: Number of repeats per wavelength (default: 5)

  • --verbose: Enable verbose output

Example:

# Scan from 400-700 nm with 5 nm steps, 2 second exposures
pb measure-pandora-throughput 2 400 700 --step 5 --ndFilter ND10 --nrepeats 10

Enhanced Throughput Scan (Beta)

Note

This command is under construction. The beta version includes additional features being tested.

pb measure-pandora-throughput-beta <exptime> <lambda0> <lambdaEnd> [options]

Additional options over the basic version:

  • --darktime <s>: Dark measurement time between light measurements

  • --flip <name>: Flip mount to activate before measurement (e.g., flipPD2)

Example:

# Scan with dark measurements between each point
pb measure-pandora-throughput-beta 1 400 700 --step 5 --darktime 0.5 --nrepeats 50

Production Throughput Scan (Final)

Note

This command is under construction but represents the most robust implementation with automatic overflow handling.

This version includes automatic handling of range overflows and proper dark measurements when the electrometer range changes.

pb measure-pandora-tput-final <exptime> <lambda0> <lambdaEnd> [options]

Options:

  • --step <nm>: Wavelength step size (default: 1 nm)

  • --ndFilter <name>: ND filter on Zaber stage

  • --nrepeats <n>: Repeats per wavelength (only successful measurements counted)

  • --darktime <s>: Dark block time (defaults to exptime if not specified)

  • --verbose: Enable verbose logging

Features:

  • Automatic dark measurement before/after range changes

  • Automatic retry of failed light measurements due to overflow

  • Only counts successful measurements toward repeat count

Example:

# Production scan from 350-750 nm
pb measure-pandora-tput-final 0.5 350 750 --step 2 --ndFilter CLEAR --nrepeats 100 --verbose

Charge Measurements

Note

This command is under construction. Charge mode measurement is experimental.

The charge measurement command uses the B2985B/B2987B electrometer in coulomb meter mode to measure accumulated charge vs wavelength. This mode integrates current over time using a feedback capacitor, which can provide better signal-to-noise for certain applications.

pb measure-pandora-charge <exptime> <lambda0> <lambdaEnd> [options]

Arguments:

  • exptime: Integration time per measurement (seconds)

  • lambda0: Start wavelength (nm)

  • lambdaEnd: End wavelength (nm)

Options:

  • --step <nm>: Wavelength step size (default: 1 nm)

  • --nrepeats <n>: Number of repeats per wavelength (default: 100)

  • --darktime <s>: Dark exposure time (defaults to exptime)

  • --discharge: Discharge capacitor before each acquisition (default: enabled)

  • --no-discharge: Skip discharge for continuous charge accumulation

  • --verbose: Enable verbose output

Example:

# Charge measurement scan from 400-600 nm
pb measure-pandora-charge 1.0 400 600 --step 5 --nrepeats 50 --verbose

# Without discharging between measurements (continuous accumulation)
pb measure-pandora-charge 1.0 400 600 --step 5 --no-discharge

Charge Mode Notes:

  • The feedback capacitor is automatically discharged (zeroed) before each measurement unless --no-discharge is specified

  • Available charge ranges: 2 nC, 20 nC, 200 nC, 2 µC

  • Auto-discharge can be configured to automatically reset the integrator when approaching range limits

Data Output

All wavelength scan commands save measurement data to the PANDORA database. The output includes:

  • Timestamps for each measurement

  • Wavelength values

  • Electrometer readings (current or charge)

  • Dark measurements (where applicable)

  • Metadata (ND filter, repeat count, etc.)

See Database Access for information on retrieving and analyzing measurement data.

Best Practices

  1. Warm-up: Allow electrometers to warm up for at least 30 minutes before precision measurements.

  2. Dark measurements: Use the --darktime option to interleave dark measurements for background subtraction.

  3. Range selection: For throughput scans, the auto-range feature adjusts the electrometer range automatically. For charge measurements, select an appropriate fixed range based on expected signal levels.

  4. ND filters: Use appropriate ND filters to keep signals within the optimal measurement range, especially at wavelengths with high source intensity.

  5. Repeat counts: Higher repeat counts improve statistical precision. Use --nrepeats 100 or more for production measurements.

Troubleshooting

Overflow errors: If you see overflow errors, try:

  • Using a less sensitive range (higher --rang0 value)

  • Adding ND filters to reduce signal intensity

  • Using measure-pandora-tput-final which handles overflows automatically

Slow scans: Reduce --nrepeats or increase --step for faster exploratory scans.

Noisy data: Increase --nplc for longer integration times, or increase --nrepeats for better averaging.

See Also