After connecting the Arduino to the computer, upload any code is unnecessary. Follow the provided circuit diagram to correctly connect the red laser (623~650 nm). Once the laser is connected, it will light up. 

Caution: Be sure to avoid direct exposure of the laser beam to your eyes to prevent injury.

Next, securely mount the red laser and the sample onto the experimental stand, as shown in the diagram below. Ensure that both the laser and sample are properly aligned and locked on the stand to ensure stability during the experiment. At this point, the setup is complete, and you are ready to begin the experiment. Be mindful of the alignment of the laser beam and the sample to ensure accurate results.

 The experiment setup involves precise positioning to capture the diffraction pattern effectively. For best results, verify the stability of all connections, check for any loose components, and confirm the laser's path to the sample before proceeding with data collection.

Project 1: Custom Slit Diffraction

Step 1: Set Up the Arduino and Laser
Connect the Arduino Uno to the power source, ensuring the laser's power wires (3.3V & GND) are properly connected. Once the red laser (650 nm) is emitting light, securely mount it on the experimental stand. Verify that the laser beam is stable and aligned in the correct direction for the experiment.

Step 2: Position the 0.3 mm Slit Plate
Place the 0.3 mm slit plate onto the experimental stand. Ensure that the laser beam passes directly through the 0.3 mm slit. Carefully adjust the alignment so that the laser light travels straight through the slit, as this is essential for forming a clear diffraction pattern.

Step 3: Set Up the Screen and Observe Diffraction Pattern
Place a black "L" screen directly in front of the laser, aligned with the beam's path. Observe the screen for diffraction fringes (alternating light and dark bands). If no pattern is visible, adjust the laser’s alignment, the path of the light, or the focus of the beam until the diffraction pattern appears clearly. Accurate alignment is crucial for a successful experiment.

Step 4: Record Observations and Measure for the 0.3 mm Slit
Once the diffraction pattern is visible, measure and record the distance DDD between the 0.3 mm slit plate and the black "L" screen. Using a camera, take a photo of the diffraction fringes. Ensure that a ruler is included in the photo for scale reference. Follow the suggested photography method (Method V2) to capture the diffraction pattern accurately, with the fringes and ruler clearly visible in the same frame.

Step 5: Analyze Using ImageJ and Calculate the Slit Width
Import the captured image into ImageJ software for analysis. Using the visible scale (ruler) in the image, measure the distance between adjacent dark fringes. Apply the diffraction equation to calculate the slit width w:

where:

• d is the diameter of the hair,

• m is an decimal representing the order of the minimum plus 0.5(e.g.,  m=1+0.5, 2+0.5, 3+0.5...)

• λ is the wavelength of the laser (650 nm),

• L is the distance from the hair to the screen,

• y is the fringe spacing (distance between adjacent bright fringes).

Step 6: Repeat the Process for the 0.4 mm Slit
Replace the 0.3 mm slit plate with the 0.4 mm slit plate on the experimental stand. Repeat Steps 1 through 5 for the 0.4 mm slit, ensuring the same alignment, measurement, and analysis process. After completing the experiment, use ImageJ to calculate the width of the 0.4 mm slit in the same manner as for the 0.3 mm slit.

Project 2: Hair Diffraction

Step 1: Set Up the Arduino and Laser
Connect the Arduino Uno and the laser’s power wires (3.3V & GND). Ensure the red laser (650 nm) emits light, then mount the laser securely onto the experimental stand. Double-check the power connections and confirm the laser beam is steady and aligned with the intended direction of the experiment.

 Step 2: Prepare and Position the Hair Sample
Take a single strand of hair and carefully attach it to a sample slide using tape or another adhesive. Ensure the hair is stretched straight across the sample without curling or slack. Place the sample slide onto the experimental stand, ensuring the laser beam passes directly through the hair. Proper alignment is critical to obtaining a clear diffraction pattern.

 Step 3: Set Up the Screen and Observe Diffraction Pattern
Position a screen directly in the path of the laser beam on the opposite side of the hair sample. The screen should be far enough away to allow for clear observation of the diffraction pattern. Observe the screen for the appearance of diffraction fringes (alternating light and dark bands). If no pattern is visible, adjust the laser’s alignment, the beam's focus, or the sample’s position until the diffraction pattern becomes clear. Fine-tuning these parameters is essential to achieving optimal results.

 Step 4: Record Observations and Measure
Once the diffraction pattern is visible, measure and record the distance D between the hair sample and the screen. Use a camera to take a clear image of the diffraction fringes. Ensure a ruler is visible in the photo to provide a scale reference for later analysis. Follow the recommended photography method to capture the image accurately, with the diffraction fringes and the ruler in the same frame.

 Step 5: Analyze Using ImageJ and Calculate Hair Diameter
Import the captured image of the diffraction pattern into the ImageJ software for analysis. Using the image's visible scale (ruler), measure the distance between the dark fringes. Based on the fringe spacing and the known distance DDD, use the diffraction equation to calculate the diameter of the hair:

where:

• d is the diameter of the hair,

• m is an decimal representing the order of the minimum plus 0.5(e.g.,  m=1+0.5, 2+0.5, 3+0.5...)

• λ is the wavelength of the laser (650 nm),

• L is the distance from the hair to the screen,

• y is the fringe spacing (distance between adjacent bright fringes).

This process will give an accurate measurement of the hair’s diameter using the diffraction pattern and the experimental setup.