Low-Cost Methods for Improving Data Collection Speed in Microwave Bragg Diffraction

In many introductory physics classes, diffraction of light is introduced first, then more advanced diffraction topics such as x-ray diffraction, Bragg’s law, and crystallography are covered. Since using x-rays raises safety concerns and atomic spacing in a crystal is not easy to change, microwaves with macroscopic crystals have been used to study Bragg’s law in the undergraduate laboratory. A number of scientific supply companies, including PASCO and 3B Scientific, sell 10-GHz microwave optics systems. However, using these systems within the parameters of the manufacturer’s procedure for a Bragg diffraction lab poses some challenges. First, the receiver and transmitter must be manually positioned, making the data collection process slow. Second, the microwaves should be plane waves and the receiver should be located beyond the far-field limit. These 10-GHz microwave optics systems are low power, making them safe for lab use, but this limits the crystal size and working distance between the transmitter and receiver to under 1000 mm. The experimental setup suggested by the manufacturer separates the transmitter and receiver by about 10 wavelengths from the center of rotation. While the bells on the transmitter and receiver help with producing plane waves, it is expected that ideal conditions for Bragg’s law are not completely fulfilled. Indeed, the experiment guide warns of errors up to 15% and unexplained peaks in the data.