Laser power in optical tweezers

In summary, the conversation discussed the alignment and power loss of an optical tweezer being used for an undergraduate thesis. The power was measured at different points and the concern was raised about whether it was enough for the application. It was mentioned that the quadrant photo diode had not been inserted yet and there was a question about its placement. The suggestion was made to ensure that the numerical apertures of the lenses were properly matched to minimize power loss. The conversation ended with the request for more information on the placement of the quadrant photo diode.
  • #1
MadMarvin
2
0
Hi,
I'm currently recalibrating an optical tweezer for my undergraduate thesis. The alignment did turn out well so far but I'm a little bit concerned about the power loss within the microscope (here's a picture of the relevant part, without prisms).
I read in a paper that 20 to 100mW are sufficient for most basic applications. I measured the power at different points (the condenser is not fully aligned yet):

Before TL2: 105 mW
After L_BFP: 10-20 mW, depending on how well the immersion oil works.

Is that enough? I use a DIC microscope, so the light passes two DMs, two prisms, objective, condenser and their respective apertures. The beam has been expanded to roughly 3,5mm, so I did not expect the power after L_BFP to be very high. But 10 mW seems too low.

Also, I haven't inserted the quadrant photo diode yet. My advisor thinks it should be placed a good deal before the focal point of L_BFP - shouldn't it be placed a little bit behind?
 
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  • #2
My first instinct would be to make sure that the NAs of the various lenses are matched properly. If you propagate from high NA to low NA you will lose a chunk of power.

Claude.
 
  • #3
Make sense, problem is: I do not even know the manufacturers of all the parts, let alone the properties of each one. I do not mind the power loss as long as the back focal plane interferometry still works so I will have to try that out, first (the diode is being repaired right now).

Anyway, thanks for your advice. Could someone elaborate on my last question, please?
 

What is the purpose of using lasers in optical tweezers?

The main purpose of using lasers in optical tweezers is to manipulate microscopic particles through the use of light. The high intensity and focused beam of the laser creates a gradient force that can trap and move small particles, allowing for precise control and manipulation in experiments.

How does the power of the laser affect the trapping ability of optical tweezers?

The power of the laser directly affects the strength of the gradient force, which is responsible for trapping particles. A higher power laser will create a stronger gradient force, allowing for the trapping of larger or more complex particles. However, too much power can also cause heating and damage to the trapped particle, so the power must be carefully calibrated for optimal trapping.

What is the typical range of laser power used in optical tweezers?

The range of laser power used in optical tweezers can vary greatly depending on the specific experiment and the type of particles being manipulated. Generally, the power can range from a few milliwatts to several watts. However, it is important to note that the power should always be carefully adjusted and monitored to prevent damage to the particles.

How is the laser power measured in optical tweezers?

The laser power in optical tweezers is typically measured in either milliwatts (mW) or watts (W) using a power meter. This device measures the intensity of the laser beam and can provide real-time feedback on the power output. It is important to regularly calibrate and check the power meter to ensure accurate measurements.

Are there any safety precautions that should be taken when using lasers in optical tweezers?

Yes, there are several safety precautions that should be taken when using lasers in optical tweezers. This includes wearing appropriate eye protection, ensuring proper ventilation in the laboratory, and following proper handling and disposal procedures for the laser and any potentially hazardous materials. It is also important to regularly check and maintain the laser equipment to prevent malfunctions or accidents.

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