Herriott Cell (Multipass Cell) Setup and Configuration (Viewer Inspired) | Thorlabs Insights

[@TushhsuT]

I actually have aligned it once (or rather participated in alignment) about 20 years ago. The only thing - we had both mirrors with an opening and light was escaping in forward direction from a laser. it was also a ring pattern. Now i know it was the Herriott cell. I have actually read the original article tha time, but did not mention authors names. As I remember, we have used the cell to create a compact optical delay unit. Both sensors (PMTs), for signal and trigger, were mounted straight on inputs of an analog 5 GHz oscilloscope to avoid any pulse stretching because of cables resistance and capacitance. So there was no way to make an electrical delay if one wanted to delay one signal over another and we made an optical one.

[@hoofheartedicemelted296]

Thanks Paul.

[@lidarman2]

Great video! This is totally coincidental but I am doing this right now in the UV around 265 nm. I am doing it from the concept of injecting light through a mirror with 99% reflectivity. But that said, I am glad to see the alignment technique and going to try to apply it to my set-up. Thank you and as always, thanks for the snacks.

[@thorlabs]

@lidarman2 That's great! We’d love to hear how it goes and if you come across any alignment tips and tricks you'd like to share - especially considering how working in the UV always has its own unique set of challenges. We’re also happy the Lab Snacks are helping to fuel your work on your Herriott cell!

[@drbhavanikumaryellapragada3286]

Very good demonstration. However for longer distance, it is difficult. I tried in my lab

[@thorlabs]

@drbhavanikumaryellapragada3286 It is exciting to hear you tried the approach in your lab, and it is interesting to hear that you applied the technique to a setup where the mirrors were farther apart. The reference cell length in the video (one focal length) always provides six passes through the cell and three reflections on the far mirror. Since this is not the case for other mirror separations, we would love to hear what mirror separation you used and whether you used a different alignment technique!

[@drbhavanikumaryellapragada3286]

@@thorlabs Dear Sir, Thank you for considering my reply. I have a small lab. I made the setup using a 650 nm CW laser and aluminium mirror which has a cut at 45 degrees angle. The reflected light is collected using a setup which has an OSA to collect the light spectrum. The resultant spectrum gives CNR of 20 dB dynamic range. I am trying to get still more but it was not possible. That's why I informed you that it is difficult for longer ranges. With best regards

[@ezdeezytube]

Can this be done across a 3 meter distance between mirrors? If so, what is the maximum possible number of reflections potentially possible?

[@thorlabs]

@ezdeezytube It is possible to have a 3 m long Herriott cell. Equations provided in the paper by Tarsitano et al. (referenced in the description) are useful for calculating the total number of reflections provided by a particular Herriott cell setup. Total reflections of several hundred are generally possible under ideal conditions. However, several non-ideal parameters can make it difficult to predict the maximum number of reflections. One is the absorbance of the medium between the mirrors, and another is the reflectivity of the mirrors. Both attenuate the beam with each pass through the cell, and eventually signal power will be too low to be useful.