2018 Conference on Laboratory Instruction Beyond the First Year. Quick Summary

Transcription

1 2018 Conference on Laboratory Instruction Beyond the First Year Quick Summary

2 Conference Format A few plenary speakers on topics related to advanced labs. Several breakout sessions related to specialized topics Two poster sessions presenting research and tips 55 workshop sessions, where participants get ~40 minutes hands on with some experiments. You could attend up to 12 of these. Most conference documents available:

3 Presentations Many of the talks and posters focused on being successful with projects Optics and Lasers, Chad Hoyt (Bethel Univ.) Experimental design labs, Melissa Eblen-Zayas (Carleton College) Developing labs with theoretical, experimental and computational goals, Ashley Carter (Amherst College). Lots of good hints on how to be successful.

4 Workshops The workshops ranged from poorly designed advertisements for equipment to hands-on experiments using the actual apparatus. Some commercial experiments seemed well done (eg. Teachspin) while others seemed to miss the point. The best were experiments/instruments developed by other instructors that gave novel experiments, new apparatus, simple ways to address learning outcomes. I d like to demonstrate two experiments I found really interesting:

5 Shoebox Spectrograph DVDs have ridges at a.74 mm pitch, allowing them to act as diffraction gratings in reflection. With a few cuts, folds, with tape and glue a remarkably useful spectrometer can be made.

6 Optical Spectra By attaching a cheap (~20$) webcam and using free software (ImageJ) the position along the camera image can be calibrated to wavelength if you have a known spectrum.

7 From Timothy Grove, Paper submitted for publication. I have detailed instructions I can share.

8 Experiment ideas: Reflected vs transmitted light spectra Measurement of an unknown gas Laser-induced PlayDoh Fluorescence Solar spectrum I like that a simple device allows students to explore without fear of a complicated apparatus. Useful for 2 nd year maybe?

9 Single Photon Avalanche Diode detector AND113R light emitting diodes break down under reverse voltage (-20 to -28 V).

10 Avalanche Breakdown In the breakdown region a single electron+hole are created from a photon, but the large reverse bias accelerates the electron, which gains enough energy to knock out other electrons. The LEDs used in this experiment were designed to emit light, but were found to exhibit avalanche breakdown.

11 Measuring Single Photons Each pulse of current corresponds to a single photon causing avalanche. The efficiency is extremely low each pulse is due to a single photon, but only one out of many photons creates a pulse.

12 Statistics By taking those pulses, connecting them to a comparator to give a digital output, the timing of the pulses were studied. The timing follows Poisson statistics.

13 Further Experiments The experiment (Jonathan Newport, American University) has several extensions: Measure the dark count of pulses by completely covering the photodetector. Create a constant source of illumination using an LED. Measure the count rate as a function of LED Current and/or luminous intensity. Investigate any dead time effects of your detection circuit by varying the resistor in series with the photodetector. Estimate the quantum efficiency of the photodetector. Investigate the effect of temperature on count rate. Investigate the spectral response of the photodetector.