Besides other things I'm very interested in lasers, the microscopic world, and to make things visible that aren't visible with normal means. I also find it a sport to use things for purposes where they are not designed for (aren't we all ;) ). Combining the above I came up with a solution for an idea I have for ages: making a Laser Scanning Microscope (LSM)! Nothing fancy as a Fluorescent Confocal Laser Scanning Microscope, but a straight forward LSM.
- An LSM works basicly as follows: highly focussed light from a light source hit point by point, row by row (X-Y plane) an object. The light, reflected from the object, wil travel back the same direction it came. A semipermeable mirror reflects this light containing data of the object to an LDR. The intensity of the reflected light is measured. A computer takes care of steering the light spot and also the image making (pic 2). -
At the same time I was wondered if it is possilble to use a DVD laser pick-up to make an LSM. Well, with some alterations, it is!
The reason I was thinking of a DVD pick-up is that it houses a laser and a lens capable of projecting a spot of visible laser light small enough to "see" a bit on a DVD. And those bits are very small (320nm)! Furthermore it houses coils to steere the lens (sideways and up and down) and a detection part. This steering is necessary to be able of following the microscopic narrow tracks on a CD or DVD while spinning (sideways moving of the lens) and follow height differences while spinning (up and douwn movement of the lens). You can imagine that folowing the track must be very precise considdering the turning speed and the bit size! These characteristics are exactly what we need!
I tested the pick-up as is:
It's turns out to be unusable in this form because:
At this stage the idea was born to use only the part that houses the lens with the steering coils. With one of these parts you can steer the lens in one axis. The other axis will be steered with another lens/coil part (as you can see later on). The result is one lens that can be moved in an X-Y plane! When (laser)light travels trough the lens when it is moving, the light spot wil follow this movement as well. This is more or less the most important part of an LSM.
there are some drawbacks to (naturally)
In this instructable I shall explane how I did this and what difficulties I encountered during the project. I think this instructable is a whole mouth full but building it is'nt really hard.
Pic 1 and 3 shows the model I work with right now. It was in the beginning of my project development a more chaotic contraption, but it did work fine!
Before you start building, a word of advice (pic 4): since this device's main part is a laser and the whole thing operates by means of concentrating and redirection by lenses and mirrors, of laser light, you have to be extremely carefull and take precautions for yourself an any bystanders not to stare directly into the beam or any reflection of it.
Like every technical hobbyist most things you need you will have already in your possession. In the past decades I have taken appart several DVD/CD players and have always saved the parts for later use. You never know!
This is the list:
for the lens part:
for the electronic part:
for the laser part:
And preferably a decapitated microscope so you can build the whole thing in a nice housing with an in height adjustable object table. You can also use the adjustable object table of an other microscope for your objects, and position the lens/laser combination in one way or another above it, as I did in the beginning of this project, and that wil work fine, but if you can lay your hand on a scrap microscope you can make things much easyer.
The point is: you really need an in height adjustable object table (otherwise you can get very stressed.). It's even better if the object table can also be adjusted in the X-Y direction.
Keep in mind that to focus with this kind of magnifications, where the focus point lies on around 1 mm distance from the lens, you have to be able to adjust the object table within hundreds of millimeters!
For the computer part:
And to make live easier:
* there are lasers with varying wavelenghts. From long to short wavelenghts there are, among others: infra red, red, green, blue and ultra violet. With ultra violet (in this list the shortest wavelenght) you can theoretical make the sharpest image because you can make the smallest light spot. I have made a few with an UV laser and it did well, but the darker colored objects are harder to capture.