Experimental tips and tricks

"Laboratory Optics" by Peter Beyersdorf is a good resource for learning hands-on techniques for running an optics experiment.

  • Description: “A multimedia interactive guide to developing practical skills for optics research. Use as a class lab manual, an instructional tool or as an indispensable reference. In concise, high-def videos, various skills and techniques are demonstrated and explained. These cover topics for the novice, such as mounting and cleaning of optics, as well as for the more advanced learner, such as balanced detection, and lock-in amplifiers.”

Optics table shutdown procedure

  1. Shut off Supercontinuum Laser:
    1. Turn down the laser power on the computer, and then quit the software.
      • Using individual clicks rather than holding down the button, lower the power and stop at zero (don't go negative).
      • You may click fairly quickly, but be careful not to click faster than it registers in the software.
    2. Turn the key off first, and then turn off the oscillator power (green button)
    3. Unplug the power if you are not going to use it for a few days.
  2. Turn off both monocromators
  3. Zero/shut off scan mirrors
    • Use DC voltage source labview program to set AO0/AO1 to 0V then unplug computer case.
  4. Turn off photodetector
  5. Unplug power meter
  6. Shut off preamps, lock-in, and chopper controller.
  7. Turn off power strip.
  8. Cover back of objective with plastic circle(for dust)
  9. Cover periscoping mirror
  10. Quit labview programs

Extracting quantum efficiency

The quantum efficiency of a CNT with absorbing length L«w where w is the FWHM of the gaussian beam can be shown to be:

ηL = (IntPC/e)/[(P/hv)*σ]

ηL is the quantum efficiency times length. IntPC is the spatially integrated photocurrent. P is the laser power, hv the photon energy, and σ the absorbtion cross section per length. This can be interpreted as the total charge extracted per unit time, divided by the number of photons absorbed by the nanotube per unit time. By using the following units:

IntPC - nA/um^2

P - W

hv - eV

σ - um^2/um

We get a result of ηL in units of um.

Important units in calculation:

Defoucsed Photocurrent - nA/mW


Required Measurements

  • Photocurrent image with known dimensions
  • Laser power at image wavelength
  • OD of your NDF(info)
  • Photocurrent resonance

During data analysis

– Integrated Photocurrent from photocurrent image

Scale image axes

Remove offset current and potentially do a FFT

Get integrated photocurrent

– Power

Add Power and OD info

– Absorbtion cross section Part 1: Diameter

First get the diameter by chiral identification of resonant peaks.

Use the diameter in the QE table to get EQE.

– Absorbtion cross section Part 2: ABCS per atom

Quick and dirty: just assume graphene abcs giving x um^2/um off resonance and x um^2/um on resonance

Exact: Get defocused photocurrent at image wavelength

Use NT diameter, peak number, and resonance PC area to calculate the conversion factor.

Calculate ABCS from these two values.

Optics

Collaborators in Nijmegen at experts in using fluorescence microscopes.

At OSU we collaborate with Vince Remcho's (Chemistry) for fluorescence microscopy.

Laser diodes

To get stable laser power out of a laser diode and good power supplier is needed. For Michael Paul's project we borrowed a Tetronix CPS250 triple output power supply from Bill Hetherington (25V 600mA).

The cheap 532 nm laser diode that Michael used does not have a good beam profile. Two options, buy and expensive laser or couple the laser to a single mode fiber.

Unit

eV to nm: 1 eV photon has wavelength 1240 nm.

Test


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