PHTN1306 Lasers III - Lab
DPSS Laser Design - Part 3 (2017F)

Introduction

While convolution (covered in the last lab) is used to predict the effect of pump diode temperature on laser output, in this lab we will experimentally determine actual small-signal gain of the laser (which embodies absorption) as a function of pump diode temperature.

Experiment:

946nm Laser Setup

The basic experimental setup: The PSU-III power supply unit controls the pump diode current (keeping it constant at 2.000 A) while the Nd:YAG amplifier temperature is kept constant by an ILX-5910C temperature controller (keeping re-absorption loss constant for this experiment). A second ILX temperature controller allows the temperature of the pump diode (and hence the pump diode wavelength) to be varied.

A Laserglow R94050XSX 946nm DPSS laser is connected such that the external ILX LDC-5910C temperature controller controls the temperature of the pump diode. This allows determination of absorption and then small-signal gain as a function of pump diode temperature (and hence emission wavelength) alone.

Program the LDC-5910C controller with the correct Steinhart-Hart parameters for the pump diode TEC. Set the diode temperature for 10C and enable the controller. Next, switch the "PSU-III" power supply on which will operate the diode at a constant pump current and the amplifier a constant optimal temp (the R94050XSX laser features a separate diode and amplifier TEC so the amplifier temp is independent). Place an optical power meter in the path of the output beam and set the wavelength of the meter appropriately - an external IR filter is not required as it is built into the laser to exclude 808nm radiation from the output.

When the temperateure of both the TEC and the amplifier have stabilized (as evident by constant output power), measure the output power of the laser.

Now, increase the diode temperature in 1C increments and measure the output power again. Continue until a temperature of 30C is reached.

Analysis:

#1: Knowing the temperature of the amplifier, calculate the re-absorption loss of the amplifier (which remains constant for the experiment).

#2: Knowing the observed output power, and parameters of the laser, use a simple homogeneous model to compute small-signal gain of the laser as a function of output power.

#3: Convert each temperature reading for the diode into emission wavelength by knowing the peak wavelength was observed to be 808.67 nm at a temperature of 24.00 C and that the wavelength temperature coefficient is 0.208 nm/C (these values were measured on the actual laser, not taken from a datasheet).

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. Show a plot of observed data in this lab including laser output power vs pump diode temperature and a second plot of laser output power vs pump diode wavelength.
  2. Assuming the optical parameters of the laser are (Nd:YAG amplifier is 1mm in length, the HR is essentially 100%, the OC 99% reflecting, and the beam diameter 0.5mm), and knowing the observed output power, calculate re-absorption loss (which remains constant throughout the experiment) and then using a homogeneous model the actual small-signal gain (g0) of the laser at 10C. Outline, explicitly, all calculations required including re-absorption loss and saturation power.
  3. Calculate the small-signal gain as a function of pump diode temperature as well as pump diode wavelength. Submit a table of pump wavelength vs. small signal gain and a plot of the same data.