[dsg-hallb_rich] [EXTERNAL] Re: Mirror reflectivity source around 400nm

[Marco Mirazita]

Hi Tyler,
you could split the measurement in two parts, first part up to 400 nm 
with one setting and second part above 400 nm with another setting.
Marco


Il 2022-04-28 16:55 Tyler Lemon ha scritto:
> Hi Marco Mirazita,
> 
>  Over the past week, I've tried to get measurements with the
> reflectivity test station at lower wavelengths so we can get data
> around 400 nm for the RICH mirrors.
> 
>  With the source we have, we can measure ~400 - 600 nm wavelengths if
> the integration time of the spectrometers is increased. However, as a
> consequence of the higher integration time, the spectrometer CCD is
> saturated above ~600 nm. Also, the counts observed around 400 nm is
> still relatively low. Attached is a plot (NEW reference-AVG.png) of
> the spectrometer counts of the reference light showing this.
> 
>  This behavior is due to the nature of the quartz-tungsten halogen
> (QTH) lamp used for the source. While the source does output some
> light (as specified) down to 360 nm, it has the highest intensity
> around 850 nm.
> 
>  Looking back at the data from RICH-1, we see the same behavior of the
> old test station, which also uses a QTH lamp. Attached is a plot
> (photodiode A by mirror and date.pdf) of current measurements from the
> control photodiode (the equivalent of the reference light in the new
> test station) for four mirror measurements taken in 2017 and we see
> the same general shape as the data from the new test station.
> 
>  With this, it's apparent that the light source in the new test
> station is comparable to the light source in the old test station.
> 
>  To be able to get more counts at lower wavelengths, we could try
> getting a filter that only passes the lower wavelength light so we can
> use higher spectrometer integration times resulting in more counts.
> Something like the Thorlabs 450-nm cutoff shortpass filter [1] or
> Newport 450-nm cutoff shortpass filter [2] would be compatible with
> our source's built-in filter holder.
> 
>  -Tyler
> 
> 
> Links:
> ------
> [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__www.thorlabs.com_thorproduct.cfm-3Fpartnumber-3DFESH0450&d=DwICAg&c=CJqEzB1piLOyyvZjb8YUQw&r=Ry65GV1L9CI4W-wouYF1Yh0O9PuhLc4ZWUkBi_Op2h8&m=eBTvltLnRWdaj4opfLzlg03ZsIP_RohM4p5I05aADP7UbYASf58bYXuJCj5M6Syx&s=zcAke1YTtfwPG-KUmNVJGfpXA1No1aSDkI1MOgiGJGQ&e= 
> [2] https://urldefense.proofpoint.com/v2/url?u=https-3A__www.newport.com_p_10SWF-2D450-2DB&d=DwICAg&c=CJqEzB1piLOyyvZjb8YUQw&r=Ry65GV1L9CI4W-wouYF1Yh0O9PuhLc4ZWUkBi_Op2h8&m=eBTvltLnRWdaj4opfLzlg03ZsIP_RohM4p5I05aADP7UbYASf58bYXuJCj5M6Syx&s=EzRVgEqoTzidU2qCllJyBp2M9gUk-_Pnq3KfiJmT_4w&e= 
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