Multiwavelength Quantum-efficiency measurement

Disclaimer: This measurement manual probably is the most incomplete of all

Rationale

The wavelength dependent quantum-efficiency [QE] of the PMT is dictated by the photocathode material and UV cutoff of the PMT glass. This measurement aims to characterize the PMT and DEgg QE at seven discrete wavelengths.

These wavelengths are:

  • 315 nm

  • 340 nm

  • 365 nm

  • 405 nm

  • 470 nm

  • 520 nm

  • 572 nm

Setup

The setup for the wavelength dependent QE measurement lives in a freezer in the ICEHAP laboratories. It is shown in Fig. 27.

../../_images/qe_vs_wl_setup.JPG

Fig. 27 Laboratory setup for the quantum-efficiency measurement.

The setup consists of a two-stage stepper motor setup, which holds the LEDs. The LEDs are arranged horizontally, so driving the horizontal stage allows for a change of wavelength. The vertical stage is only used at the beginning of the measurement to calibrate to the correct height.

The light travels from the LEDs through two adjustable collimators and enters a beamsplitter. This beamsplitter needs to be calibrated before the QE measurement is done. One beam leads to the reference PMT, that is absolutely calibrated by Hamamatsu, the other leads to the DEgg or DEgg-PMT. For the beamsplitter calibration, another absolutely calirated reference PMT can be mounted instead of a DEgg.

The LEDs are driven by a function generator that sits in the rack next to ratafia. That rack also contains HV supply for the small reference PMT on channel 1. The low voltage supply for the DEgg HV bases is also located in that rack, see Fig. 28.

../../_images/rack_stack_eq_vs_wl.JPG

Fig. 28 Power supplies and function generator in the rack next to ratafia.

Since the function generator only has one output, the signal cable needs to be connected manually to the correct LED when changing to another wavelength.

Running the DAQ

The reference PMT should be supplied with 1550V.

Some go-to settings for the function generator are (to be updated):

  • width 30-50ns for every wavelength

Some settings differ for the LEDs:

  • 315nm: Offset=2.5V, Amp=5Vpp

  • 340nm: Offset=2.5V, Amp=5Vpp

  • 365nm: Offset=2.5V, Amp=5Vpp

  • 405nm: Offset=0.5V, Amp=5Vpp

  • 470nm: Offset=700mV, Amp=5Vpp

  • 520nm: Offset=700mV, Amp=5Vpp

  • 572nm: Offset=2.5V, Amp=5Vpp

The DAQ lives in a jupyter notebook on ratafia. It can be found at:

/home/icecube/worksheets/multi_lambda_qe_meas.ipynb

This notebook contains the DAQ for the actual measurement, beamline calibration, and gain measurements.

First, the motorstages are initialized. The assignment of the stages to ttyUSB ports is not consistent over time. Please make sure that the correct ports are assigned to the stage objects in the notebook. Just drive one stage and observe the movement in the freezer.

Analysis

The analysis scripts are located at:

/home/icecube/yuya/multi_wl_qe

The README in that directory gives a short overview of what to run.