Construction of a Tabletop Michelson Interferometer
The pupose of this page is to describe the work being done in the construction of a tabletop Michelson Interferometer. The purpose of this device in the scope of the project is two fold. First, the interferometer can be used to analyze te vibrational characteristics of a diamond waffer suspended from a wire frame. Second, the interferometer can be used to study the surface profle of a diamond waffer, allowing us to see the efects that different cutting and mounting tecniqus have on the final product.
Construction
Parts List
The following is a lis of the prts used in the construction of the inerferometer, along with a brief descripton of the parts.
| Category | Item | Description |
| Beam Splitter | Beam Splitter Cube | (2cm)3, AR, 400-700nm |
| Kinematic Platform Mount | (2in)2 | |
| Prism Clamp | Large clamping arm | |
| Camera | Casio Ex-F1 | |
| Mirrors | Protected Silver Mirror | 25.4mm Dia., R≈98% |
| Mirror Holder | Standard 1" holder | |
| Kinematic Mirror Mount | Adjustable Kinematic mount for 1" holder | |
| Light Source | 532nm Green laser Module | 5mW, 5mm spot size, <1.4 mrad div. |
| Kinematic V-Mount | Small Mount with Attached Clamping Arm | |
| Beam Expander/Spatial Filter | Pinhole | 5μm, 10μm, 15μm, and 20μm pinholes |
| Pinhole Holder | 1/2" and 1" standard holder | |
| Small Plano-Convex Lens | f=50mm, 12.7mm Dia., AR coating | |
| Lens Holders | Holder for 1/2" and 1" optics lenses | |
| Large Plano-Convex Lens | f=150mm, 25.4mm Dia., AR coating | |
| Translation Stages | Small Linear Translation Stage | 1 dimension translation stage |
| 3-Axis Linear Translation Stage | 3 dimension translation stage | |
| Common Mechanics | Posts | 3/4" and 1" high posts, 1/2" Dia. |
| Post Holders | 1" high post holders | |
| Safety Equipment | Laser Safety Glasses | Green and Blue laser beam protection |
Images of Set-up
The fllowing are images of the complete Michelson set-up
Estimating Camera Sensitivity
It is critical to understand the sensitivity of the camera to light from the interferometer, given the high intended image acquisition speed. The camera purchased for this setup, Casio EX-F1, has a movie frame rate capability of 1200 Hz. The following information allows an order of magnitude estimate of the sensitivity. (The camera uses a CMOS sensor. Note that lx=lm·m2)
- a sample CMOS chip, Micron's MT9P401, has sensitivity of 1.4 V/lx·s and supply voltage of 2.8 V yielding 2 lx·s of light energy to saturation.
- Light intensity conversion - 320 lm/W given:
- a 100 W incandescent light bulb is measured to have the perceived intensity of about 1600 lm
- a rough figure of efficiency for a 100 W is 5%
Using these conversions, the sensor pixels saturate at 6.3×10-3 W·m2·s. At 1200 Hz acquisition rate, assuming 100% duty cycle, the saturation figure is 5.2×10-6 W·m.
Now, let us assume that only about 5% of 1 mW laser light reaches the sensor due to cleanup in the beam expander and the light transmitted through the diamond. If the light is expanded to a 2 cm diameter beam, the beam at the sensor is rated at 1.6×10-8 W·m2
The two order of magnitude shortfall means that very little of the dynamic range of the sensor will be used, leading to a low signal to noise ratio. For this reason, a 5mW laser was chosen over a 1mW.
Camera Calibration
Analysis of videos taken of the vibraton of the diamond waffer can lead to information about both the frequency and the apmlitude of vibration. To perform simultaneous measurments of both parameters, a precise camera calibration was necessary.
Calibration Set-Up
The following is an image of the device sed or the camera caibration:
IMAGE OF CALIBRATION DEVICE
The cameara was mounted at one end of a 1.40m long rod. The ro was free to rotate about a pivot locaed opposite to the camera. Above the pivot