PHTN1306 Lasers III - Lab
DPSS Laser Design - Part 3 (2018F)

Introduction

In this part of the lab, the characteristics of the pump diode for the DPSS target design laser are determined. These parameters (spectrum and wavelength characteristics) will be used as the input for a convolution simulation (in the same manner as described in section 5.7 of Laser Modeling) predicting the effect of diode temperature on DPSS laser output.

Experiment:

Using the same AL0808F2000 diode as lab #2, operate the diode at a constant current of 2.2A.

Set the temperature for 10C and enable the temperature controller. Next, switch the diode power supply on and operate it at a constant current of 2.2A. Direct the into a fiber and then into an OSA. Adjust the fiber until the spectrum of the pump diode is seen around 808nm.

When the temperature of the TEC has stabilized, capture the spectrum of the pump diode as well as the peak wavelength of the spectrum. The spectrum must be captured at a resolution of 0.2nm - output values will be in units of dBm which may then be converted into linear units (e.g. mW).

Observe the peak wavelength of the output spectrum at 10C, 15C, 20C, 25C, and 30C and capture the actual output spectrum (every 0.2nm) at 10C, 20C, and 30C). As temperature increases we expect to see the wavelength shift to longer values but hopefully the spectrum remains relatively constant.

Convolution

Complete a simulation as per discussed in the lecture. The absorption spectrum of Nd:YAG is required - one source of absorption data is the Laser Database from Nasa Langley Research Center . Ensure you have values every 0.2nm to produce a table of data as a starting-point.

Complete a Simulation (using the convolution technique) predicting how pump diode wavelength shift will affect Nd:YAG DPSS output based solely on absorption of the pump radiation. Assume a diode with the spectrum as determined in the lab (i.e. those power values you digitized at intervals of 0.2nm). Produce the following:

Assignment

Hand In a WORD PROCESSED (not handwritten) lab assignment as follows. Put each question on a new page and ensure each page has a title "Question 1", "Question 2", etc. Also, please ensure the lab report is in a folder for submission (no loose pages).

To be done individually ...

  1. Submit a table of values outlining the spectrum of the pump diode at increments of 0.2nm for each of the three temperatures . The table must include columns of wavelength (every 0.2nm), power observed (in dBm), power observed (normalized, in mW). The normalized power is obtained by scaling the output power so that the peak value is 1mW (0 dBm) and all other powers observed are converted into linear units and scaled accordingly.
  2. Produce three graphs from the normalized data above showing the output spectrum at each of the three temperatures. This will allow comparison of the spectra to determine if it is a function of temperature.
  3. Submit a graph of peak diode wavelength (in nm) vs. diode temperature. Include an analysis: add a best-fit line and determine an equation relating wavelength to temperature in the form Wavelength(nm) = fn(Temperature).
  4. Show a table of data showing the absorption of Nd:YAG vs. wavelength, every 0.2nm. This data must completely cover the spectrum over which the diode emits at all temperatures between 10C and 30C.
  5. Show a printout detailing the convolution model employed. All column and row references must be visible in this picture (to do this, select an active area to print, and under the print preview menu select row/column references).
  6. Provide a summary of the convolution formulae used: simply CUT and PASTE the formula used for the first two convoluted row cells (which will contain cell references) or present a spreadsheet printout with all formulae shown instead of values (FORMULA menu, SHOW FORMULAS option). They must be legible and in a font size of at least eight.
  7. Produce a graph showing the predicted output power (y axis) vs. the wavelength (x axis). The wavelength range required is 800nm to 810nm. On the SAME graph, show the absorption of Nd:YAG on a secondary axis so both graphs are visible.