Hi Thanigachalam,

   Can you share the information about the laser source used for the theoretical calculations?

Hi Lenror Li,

A 840nm, 15mW diode laser emits a collimated output beam with a diameter of 3mm.

Thanigachalam P 

Hi Thanigachalam,

    What is your theoretical calculation method for obtaining the result? Does the laser source have other parameters such as divergence and beam quality?

Hi Lenror Li,

I assumed the beam to be perfectly collimated, implying negligible divergence, and hence assigned an m² value of 1.

Thanigachalam P

Hi Thanigachalam,

How do you obtain the data and verify its accuracy?

“According to theory, I expect the spot size to be approximately 44 microns at the lens, around 90 microns at the cornea, and roughly 280 microns at the retina.”

Hi Lenror Li,

Apologies for any confusion. The beam from the objective lens converges at a distance of 34mm. Will this information suffice, or do you require additional data? The attached Zemax file contains the complete design.

Thanigachalam P

 Hi Thanigachalam,

       I cannot find the data you obtained theoretically in the file, so I wonder how you obtained the data.

Hi Lenror Li,

For basic calculations, regardless of the system, I treated the entire setup as a single lens with a back focal length of 34mm. Considering an input of a collimated beam with a diameter of 0.8mm, an M² value of 1, and a wavelength of 840nm, I calculated the waist size at the focal point to be approximately 45 microns, utilizing the formula:

2𝑤0=4𝑀2𝜆𝑓/𝜋𝐷​

Without factoring in human eye refractive index and aberrations, I estimated the waist size at a distance from the focal point to the cornea (~3.6mm) to be around 100 microns and from the focal point to the retina (~18mm) to be about 300 microns, using the formula:

𝑤(𝑧)=𝑤0⋅ sqrt[1+(𝑍/𝑍𝑟)^2]

Despite these basic estimations not approximately also aligning with my zemax POP data.

​Thanigachalam P

Hi ​Thanigachalam,

      Yes, basic calculations can acquire data through formulas, and I believe there is no error.

And when you input the correct source parameter into the POP data, you can obtain the same result.

Hi lenror Li,

Thank you for your feedback. According to the theory, the waist size should be 45 microns. However, I noticed that the input provided indicates a waist size of 1.46mm. Could you kindly provide clarification on the reasoning behind this deviation?

Thanigachalam P

Hi ​Thanigachalam,

     I misunderstood your previous idea; I believe the POP data is correct because when I simulate with the perfect laser system, I obtain the same result. The differences in the data you obtained may be due to the aberrations of the lens system.

Hi ​Thanigachalam,

This article may help you.

Paraxial gaussian beam data | Zemax Community

Hi Lenror Li,

Thank you for your information. 

Thanigachalam P