光電檢測(cè)技術(shù)英文-wenkub.com
2025-07-10 21:30 本頁面
【正文】 to the surface of the table, the astigmatic distance will be zero.Different laser structures will have different angular beam divergences and, thus, different astigmatic distances. If you have access to several different laser types (gain guided, index guided), it may be instructive to characterize their astigmatic distances. Frequency Characteristics of Diode LasersIn order to study frequency characteristics of a diode laser, we will employ a Michelson interferometer to convert frequency variations into intensity variations. An experimental setup for examining frequency and, also, amplitude characteristics of a laser source is illustrated in Figure .1. In this experiment, it is very possible that light may be coupled back into the laser, thereby, destabilizing it. An optical isolator, therefore, will be required to minimize feedback into the laser. A simple isolator will be constructed using a polarizing beam splitter cube and a quarterwave plate. We orient the quarterwave plate such that the linearly polarized light from the polarizer is incident at 45176。m further away from the lens.5. Move razor blade 1 in the x direction across the beam through the beam spread θx and record the x position and detected intensity at each increment (≤100 181。m increments). The expected output is shown in Figure . The derivative of this curve yields the intensity profile of the beam in the x direction from which the beam diameter is determined.6. Repeat with razor blade 2 for θy in the y direction.7. Move the laser closer to the lens in increments (≤50 181。 to the principal axes of the quarterwave plate so that light emerging from the quarterwave plate is circularly polarized. Reflections change leftcircular polarized light into rightcircular or vice versa so that reflected light returning through the quarterwave plate will be linearly polarized and 90176。m. Repeat Steps 5 and 6 at each z increment, recording the z position.8. Using the collected data, determine the beam intensity profiles in the x and y directions as a function of the lens position z. This is done by differentiating each data set with respect to position. Then, calculate the beam diameter and plot as a function of z. The difference in z for the minimum in θx and θy is the astigmatic distance of the laser diode. Use of puter software, especially in differentiating the data, is highly remended.If the laser junction is not parallel to the table surface, then for each measurement above, you will obtain an admixture of the two beam divergences and the measurement will bee imprecise. If the laser is oriented at 45176。英文原文 Experimental SetupDue to the many concepts and variations involved in performing the experiments in this project and also because of their introductory nature, Project 1 will very likely be the most time consuming project in this kit. This project may require as much as 9 hours to plete. We remend that you perform the experiments in two or more laboratory sessions. For example, power and astigmatic distance characteristics may be examined in the first session and the last two experiments (frequency and amplitude characteristics) may be performed in the second session. A Note of CautionAll of the above ments refer to singlemode operation of the laser which is a very fragile device with respect to reflections and operating point. One must ensure that before performing measurements the laser is indeed operating singlemode. This can be realized if a single, broad fringe pattern is obtained or equivalently a good sinusoidal output is obtained from the Michelson interferometer as the path imbalance is scanned. If this is not the case, the laser is probably operating multimode and its current should be adjusted. If singlemode operation cannot be achieved by adjusting the current, then reflections may be driving the laser multimode, in which case the setup should be adjusted to minimize reflections. If still not operating singlemode, the laser diode may have been damaged and may need t
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