Detection and Stimulation Head

The Detection and Stimulation Head (DASH) provides easy access to new technologies, new signals and new measurement methods. The DASH is fully automated and contains LED modules for optical stimulation, a filter changer and a detector changer (optional). The DASH can accomodate a variety of attachments such as the single grain attachment and the spectrometer. The DASH can be retrospectively fitted to existing Risø TL/OSL Readers. The DASH is modularised into four layers:

  • Optical stimulation unit (bottom layer)
  • Filter changer (middle two layers)
  • Detector changer (top layer)


Optical stimulation

The OSL unit has 7 reflector modules for mounting LEDs. The modules may be equipped to the requirements of the user but the standard configuration is:

  • 2 blue modules (470 nm, ~80 mW/cm2)
  • 2 green modules (525 nm, ~40 mW/cm2)
  • 3 infrared modules (850 nm, ~300 mW/cm2)

The OSL unit includes an empty position to enable the use of external light stimulation sources such as the violet laser and single grain attachments or a user-supplied stimulation source.

The LED intensity can be fixed (CW), linearily modulated (LM-OSL) or pulsed (POSL). For optimal linearity and stability the LEDs are controlled using photo-diode feedback regulation and held constant at any power level between 0 and 100%.

Detector changer

The detector changer can accommodate up to three detectors. The DASH is fitted with collimating optics shared by all detectors. The optics are optimised for maximum transmission or, if the EMCCD camera is fitted, the best compromise between minimum non-linear distortion and maximum optical transmission.

The standard PMT is:

  • Electron Tube PDM 9107Q-AP-TTL-03 (160-630 nm)

Other detection units available are:

  • a cooled PMT Hamamatsu H7421-50 (380-890 nm),
  • a cooled PMT Hamamatsu H7421-40 (300-720 nm),
  • an EMCCD camera (Photometrics Evolve 512) with automatically adjustable focusing optics,
  • and a spectrometer system (Andor EMCCD camera mounted on a Shamrock 193 spectrograph).

Filter changer

The filter changer consists of two layers, each with 4 positions for standard commercially available 25 mm diameter filters. The filters can be stacked up to a thickness of 7.5 mm in each of the 8 filter holders.

A typical configuration of filters is:

  • Layer 1
    • U-340, 5 mm
    • Blue filter pack (BG3, 3 mm and BG39, 2 mm)
  • Layer 2
    • U-340, 2.5 mm
    • neutral density for PMT deadtime measurement
17 DECEMBER 2018