Detailed setup description

We would like to measure the reflectivity and transmittivity of UV light on samples of detector materials. Also, we want to investigate if there is any fluorescence. Here we describe in detail how we would like our setup to work, and what needs to be done for that. [PLEASE ADD ANYTHING YOU CAN THINK OF!]

Samples of detector materials

The samples that we would like to study the optical properties of, are materials used in (large scale) liquid xenon dark matter experiments (or other experiments using the same principle). We would like to investigate how the UV scintillation light generated by events in the liquid xenon interacts with the walls of the detector. We need to be able to place the samples into our experiment without touching the face of the sample, and we need to be able to measure for different angles of incoming light. A sample holder has been designed by Casimir van der Post for this purpose [MAKE A DEDICATED PAGE FOR SAMPLE HOLDER DESIGN?].

TO DO

• test placing the sample holder inside the vacuum chamber
• test rotation of the sample holder inside the vacuum chamber
• test placing samples in the sample holder
• test the thermal connection between the samples and the sample holder
• ...

UV light

Xenon scintillation light has a wavelength of 178 nm. We do not want to use any xenon in this experiment so we use a deuterium lamp and a monochromator to generate light of a wavelength in the UV region. The light will pass through a magnesium fluoride window from the lamp into the monochromator. Inside the monochromator, a reflective grating selects a specific wavelength. We can tune the wavelength using the stepper motor in the monochromator. The size of the beam can be controlled by the size of the entrance and exit slits of the monochromator.

UV light is absorbed by oxygen, therefore we perform the experiment inside a vacuum chamber. For a large enough intensity, we need a vacuum of less than (one times ten to the power minus five) mbar [INSERT REFERENCE TO CALCULATION]. We use a vacuum pump to pump the vacuum chamber, so the components of the chamber, as well as the components inside the chamber need to be cleaned (dust or lint could break the pump, as well as contaminate the reflective grating or window in the monochromator). Depending on the loss of intensity over one measurement, we could use a cold trap to catch hydrocarbons before they can coat the window from the lamp. We have a pressure gauge to monitor the pressure inside the vacuum chamber which needs to be read out.

Fluorescence of the material will not be in the UV range. We have two different non-UV sensitive (6mm?) SiPMs for measuring fluorescence.

TO DO

• clean all components
• check the complete setup for leaks
• ...

Measure

The reflected or transmitted light of the sample will be measured using (an array of) special UV sensitive silicon photomultipliers (SiPM). For fluorescence measurements we can use normal SiPMs (measure simultaneously with transmittance?). The SiPMs will be mounted on a sensor holder that can be rotated around the sample holder so we can measure the distribution of light. The intensity of light is expected to be low, so we would like to be able to see single photons. The angle of the SiPM with respect to the sample needs to be registered [MANUALLY?], as well as the signal from the SiPM. We need to get the signal from the vacuum chamber to the outside without introducing too much noise. Then, outside the vacuum chamber, we need to filter and amplify the SiPM signal and count single photoelectron peaks. Since the SiPM dark count rate is very sensitive to temperature, we also need to measure the temperature inside the vacuum chamber.

TO DO

• design, create and test a sensor holder for the SiPM(s)
• create and test a connection from the SiPM to the bias voltage and to the filter/amplifier outside the vacuum chamber that is vacuum proof and low noise
  • use temporarily a single SiPM readout and add extra wires
  • eventually get a readout system like XAMS (SiPM powersupply and pre-amp) (estimated availability: February 2023??)
• design, create and test a counter for single photoelectron peaks
  • get a digitizer (4ns resolution with ZLE)
• design, create and test a data acquisition system from the counter output
  • get a digitizer (4ns resolution with ZLE)
• solve noise issues with the lamp and the vacuum feedthroughs
• test the temperature sensors in the vacuum chamber
• use proper cables and connectors everywhere
• put electronics in closed boxes with connectors
• update the wiki
• ...