Alignment Table of Contents

• Alignment procedure home page

• Steering/Leveling of the pump laser (you are here)

• Down Conversion: alignment of A/B detectors

• Polarizing Beamsplitter: alignment of B'

• Interferometer Alignment

• Hardy's Test

Setting up the 405nm Pump Laser

This is the first (and easiest) step in correctly setting up the single photon interference experiment.

Step 1: Irises

The steering of the blue beam requires two irises, and the leveling requires that these irises be at the exact same height. Here is how you can get two irises to be the same height:

1. With the blue laser in its mount, turn it on and place one iris about an inch from the mouth of the laser. Note its location, and makes sure there's no chance for the laser to harm anyone or anything.

2. Put on a pair of orange laser goggles, and look to the dot where the beam stops (use the wall or a piece of paper). Close the iris partway, and move it around both horizontally and vertically until the dot reaches a visual maximum.

3. Next close the iris as far as it goes, and repeat until visually at maximum.

4. Take the second iris and place it in the exact same spot as the first, and repeat the process again.

Be sure to level at least one more iris to use later as a beam height gauge.

Step 2: Leveling the laser

With two irises of exactly the same height, place one iris close to the mouth of the laser and one iris far away. Turn the two screws on the laser until the beam of the laser fully passes through both irises, ensuring that the beam is parallel to the table.

Step 3: Mirrors

Now that the irises are level, place your blue laser where it will be for the remainder of the experiment. Place two silver mirrors such that the laser hits the center point of the mirrors, and reflects the beam 90 degrees. Place them such that the beam points down the length of the table, parallel to the hole.

Step 4: Mirror-Walking

THIS IMAGE IS NOT ENTIRELY CORRECT: Iris #1 (I1) should be placed AFTER Mirror #2 (M2)

Note: to mirror-walk, at least two mirrors and two irises are required.

Place the first iris in front of the second mirror. Then place the second iris down the length of the table about 50-55 inches/holes from the first iris. Now you will learn to mirror-walk the beam so that it goes directly through the center of both irises. This is the same procedure that you did in the Optics Exercise.

To mirror-walk a laser beam, you must utilize the vertical and horizontal adjustment knobs on the two silvered mirrors to guide the beam. Before beginning, make sure that the mirrors are roughly aligned by physically turning them in their mounts. Next, close the first iris (I1), and open the second (I2). Adjust the H/V knobs on the first mirror (M1) such that beam goes through the closed iris. Similarly to Step 1, observe the laser dot on the wall while wearing goggles (to reduce laser dispersion effects) and adjust the knobs until the dot reaches a maximum intensity.

Next, open I1 and close I2. Adjust the H/V knobs on M2 such that the beam goes through the closed I2, making a maximum brightness dot on the wall behind it. Next close I1, and open I2, repeat. Continue this back-and-forth process until satisfied. You will not be satisfied until the beam goes through both irises when they're closed and makes a maximum brightness dot on the wall.

Finally, block the beam with a beam-blocker behind I2.

With this, the blue pump laser is properly steered and leveled.

Move onto Down Conversion Alignment