The Pulsar Engineering Community Board

Hi all,

We’ve recently completed the full alignment procedure for our OpenRaman system, following the guide carefully. For the alignment step using a neon lamp, we captured a spectrum that looked similar to the images below – though after realignment, the lines appeared straighter, more centered, and significantly sharper.

However, when we switch over to test a real sample using the 532 nm laser (in this case, isopropyl alcohol), we aren’t getting a Raman signal. Instead, the output is just a noisy, flat spectrum with no distinguishable peaks.

We’ve confirmed:

The laser is on and focused on the sample

The sample is placed in a clean glass vial

The spectrometer is still aligned as confirmed via the neon lamp test

Integration time and gain have been increased appropriately to try and capture signal

Is there something obvious we might be missing in the transition from the neon lamp test to a real sample measurement? We’re wondering if it’s an issue with the laser coupling, sample scattering, or something else entirely.

Any help would be appreciated!

Thanks,
Eli

Hi,

This is typical of the first trials at aligning the spectrometer You can see the neon spectrum without the spectrometer being "fully" aligned.

you need to recheck the alignment procedure using the frosted glass disk. The alignment needs to be correct within 0.01-0.05° for this to work!

Also, based on the images you provided, I can see that the neon signal is slanted. You will want to correct camera orientation to get it as horizontal as possible. Based on the contrast, I would say that you also took the measurement without the lid on - also, something you want to avoid.

Thanks for your response!
Update:
We’re still trying to get a usable Raman signal and wanted to add some details about our current setup:

We’re using a makeshift pinhole (not the standard one from the kit), and we did not use the frosted alignment discs during the alignment process. We're wondering if that might be a contributing factor.

We’ve rechecked the alignment with the neon lamp and are confident it’s good—the lines are sharp, centered, and vertical. But with the laser and isopropyl alcohol, we’re still getting just a noisy spectrum.

Any thoughts on whether the pinhole or lack of frosted discs could be causing issues with laser coupling or signal detection? Appreciate any guidance!

Thanks again,
Eli

Can you describe what is a makeshift pinhole ? I'm not familiar with the term.

To answer shortly, it is absolutely necessary to have an alignment strategy/tooling. Frosted disks are one solution but not the only one.