Alluxa 1 A Ca K filter


Filter Test method f-ratio Surface  measured FWHM BW at 10% peak transmission delta CWL
Alluxa Ca K 1 A
Sol'Ex spectro
(fc=fi=125 mm)
f-115
10 micron × 4.5 mm 1.4 to 1.5 A 4.3 A + 0.5 to 0.6 A (at about 30°C)
Sol'Ex spectro
(fc=fi=200 mm)
f-115 10 micron × 4.5 mm 1.40 A 4.4 A - 0.35 A (at 14°C)
Alluxa 1 A Sol'Ex spectro f-22 10 micron × 4.5 mm 1.45 A at normal incidence
1.55 A with 1.3° tilt
4.4 A +0.3 A at normal incidence (at about 30°C)
+0.1 A with 1.3° tilt
Alluxa 0.38 nm + Alluxa 1 A

Sol'Ex spectro


f-22


10 micron × 4.5 mm

 1.3 A, both filters at normal incidence
0.9 A, both filters tilted
(non symetrical profile)
3.6 A
4.6 A
(non symetrical profile)
+ 0.5 A, both filters at normal incidence (at about 30°C)
0.0 A, both filters tilted  (at about 30°C)
Alluxa 0.38 nm + Alluxa 1 A Sol'Ex spectro f-20
(telecentric optics)
10 micron × 4.5 mm 1.1 A
(symetrical profile)
3.3 A
(symetrical profile)
0.0 A (at about 21°C)
Alluxa 1 A Sol'Ex spectro f-14.7 10 micron × 4.5 mm 1.7 A, at normal incidence 4.5 to 4.6 A 0.0 to 0.1 A (at about 30°C)
Alluxa 1 A Sol'Ex spectro f-7.3 10 micron × 4.5 mm 2.5 A, at normal incidence 5.9 A -0.7 A

 

General information on this filter:
- one-cavity filter,
- fused silica substrate (0.04 A/°C temperature drift),
- 25.4 outside diameter.




Low resolution transmission profile

(Ocean Optics HR4000, 0.27 nm sampling)



NB : peak transmission on Ca K line is not relevant because of the low spectral resolution.



Measurement in collimated beam

#1 - Optical set-up:
Sun => Sol'Ex spectrograph with 10 micron s
lit : 10 micron × 4 mm. 200 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 200 mm f.l. imaging lens. ASI290 camera.
12-bit acquisition. Dispersion:
0.05822 A/pixel.
Very transparent blue sky. Temperature: 14°C.
3 April 2023.





The fit with a Lorentzian curve is quite good (one-cavity filter), and gives : FWHM = 1.40 A, CWL = -0.35 A



#2 - Optical set-up:

Sun => Sol'Ex spectrograph with 10 micron s
lit : 10 micron × 4 mm. 125 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 125 mm f.l. imaging lens. ASI290 camera.
12-bit acquisition. Dispersion:
0.0932 A/pixel.
Very transparent blue sky. Temperature: about 30°C.
11 and 12 July 2022.



The filter is exposed to nearly perfect collimated light beam: converging light beam with a 0.5° cone (solar disk), equivalent to f-115 ratio. The surface of the filter sampled is set by the slit size (10 micron x 4 mm)

The following three images show:
- the solar spectrum near Ca K and H,
- the spectrum transmitted by the Alluxa filter at normal incidence,
- same image with different vizualisation thresholds.





Transmission profile at normal incidence in collimated beam



Measures on July 11st and 12nd give identical results. With direct reading on the graph: FWHM = 1.4 A, bandwidth at 10% peak transmission = 4.3 A, delta CWL = +0.6 A


The fit with a Lorentzian curve is quite good (one-cavity filter). Results are consistent with the previous ones: FWHM = 1.4 to 1.5 A, CWL = +0.5 to 0.6 A





Influence of temperature on CWL : measurement at 4°C

Optical set-up:

Sun => Sol'Ex spectrograph with 10 micron s
lit : 10 micron × 4 mm. 125 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 125 mm f.l. imaging lens. ASI290 camera.
12-bit acquisition. Dispersion:
0.0932 A/pixel.
Very low Sun (atltitude = 20°). Temperature: 4°C.
12 December 2022.

 

Resulting temperature coefficient is 0.04 A/°C (consistent with Alluxa data).



Measurement in a f/22 beam

Optical set-up:

Sun => Takahashi TOA 150 => Baader FFC => EO 394-10 nm => Alluxa Ca K 0.38 nm => Sol'Ex spectrograph with 10 micron s
lit : 10 micron × 4 mm. 125 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 125 mm f.l. imaging lens.
ASI290 camera. 12-bit acquisition. Dispersion: 0.0932 A/pixel.
Very transparent blue sky. Temperature: about 30°C.
18 July 2022.



The following three images show:
- the solar spectrum near Ca K and H,
- the spectrum transmitted by the Alluxa 1A filter at normal incidence. The thin dark line on the left on the bandpass is the core of the Ca K line (K3),
- the spectrum transmitted by the Alluxa 1A filter tilted by 0.8°,
- the spectrum transmitted by the Alluxa 1A filter tilted by 1.5°. The bandpass is centered on the core of the Ca K line (K3).



The FWHM increases by 0.1 A when the filter is tilted by 1.3° while the delta CWL reduces from +0.3 A to +0.1 A.



Curve fitting the curves with a Lorenztian function gives nearly identical results (FWHM = 1.44 A and 1.53 A, delta CWL = +0.3 A and 0.1 A)



Measurement in double-stack configuration (Alluxa 0.37 nm + Alluxa 1 A) in a f/22 beam

Optical set-up:

Sun => Takahashi TOA 150 => Baader FFC => Alluxa Ca K 0.38 nm => Alluxa Ca K 1 A => Sol'Ex spectrograph with 10 micron s
lit : 10 micron × 4 mm. 125 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 125 mm f.l. imaging lens.
ASI290 camera. 12-bit acquisition. Dispersion:
0.0932 A/pixel.
Very transparent blue sky. Temperature: about 30°C.
13 July 2022.



The following three images show:
- the solar spectrum near Ca K and H,
- the spectrum transmitted by the double-stack combination (0.37 nm + 1 A) at normal incidence. The arrow points to the core of the Ca K line (K3) visible as a faint dark line.
- the spectrum transmitted by the double-stack combination (0.37 nm + 1 A) tilted in ordre to have the CWL on the core of the Ca K line. Each filter is tilted separately.





When both filters are at normal incidence (left graph), the FWHM of the double-stack combination is 1.3 A and the delta CWL + 0.5 A (same as in single-stack combination).

When both tilted are tilted (right graph), the
FWHM of the double-stack combination is 0.9 A, and the peak of transmission centered on the core of the Ca K line.





Measurement in double-stack configuration (Alluxa 0.37 nm + Alluxa 1 A) in a f/19.9 telecentric beam

Optical set-up:

Sun => Takahashi TOA 150 => Airylab telecentric => Alluxa Ca K 0.38 nm => Alluxa Ca K 1 A (normal incidence)  => Sol'Ex spectrograph with 10 micron s
lit : 10 micron × 4 mm. 125 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 125 mm f.l. imaging lens.
ASI290 camera. 12-bit acquisition. Dispersion:
0.0932 A/pixel.
Blue sky. Temperature: about 21°C.
6 October 2022.

The following three images show:
- the solar spectrum near Ca K and H,
- the spectrum transmitted by the 1 A Alluxa filter at normal incidence. The very thin dark line at the center of the bandpass is K3 line.
- the spectrum transmitted by the double-stack combination with the 0.37 nm optimally tilted and the 1 A at normal incidence. The very thin dark line at the center of the bandpass is K3 line.









Measurement in a f/14.7 beam (#1)

Optical set-up:
Sun => Takahashi TOA 150 stopped at 75 mm => Edmund Optics 394-10 nm => Alluxa Ca K 1 A at normal incidence => Sol'Ex spectrograph with 10 micron × 4 mm slit. 125 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 125 mm f.l. imaging lens.
ASI290 camera. 12-bit acquisition. Dispersion:
0.0932 A/pixel.
Very transparent blue sky. Temperature: about 30°C.
12 July 2022.

The following three images show:
- the solar spectrum near Ca K and H (with the EO394-10nm filter),
- the spectrum transmitted by the Alluxa 1 A (normal incidence) and EO394-10 nm filtersand f/14.7 beam. Ca K3 is right at the center of the bandpass of the filter (thin dark line).
- the photospheric limb and chromosphere fringe with the Alluxa 1 A (normal incidence) and EO394-10 nm filters at f/14.7.





The following three images show:
- the solar spectrum near Ca K and H (with the EO394-10nm filter),
- the spectrum transmitted by the Alluxa 1 A (normal incidence) and EO394-10 nm filters at f/14.7. Ca K3 is right at the center of the bandpass of the filter (thin dark line).
- the spectrum transmitted by the Alluxa 1 A (normal incidence), Alluxa 0.37 nm (tilted) and EO394-10 nm filters at f/14.7 beam. The blockage of the wings of transmission is much better when the Alluxa 0.37 nm is stakked on the Alluxa 1 A.







Measurement in a f/14.7 beam (#2)

Optical set-up:
Sun => Takahashi TOA 150 stopped at 75 mm => Edmund Optics 394-10 nm => Alluxa Ca K 1 A at normal incidence => Sol'Ex spectrograph with 10 micron × 4 mm slit. 125 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 125 mm f.l. imaging lens.
ASI290 camera. 12-bit acquisition. Dispersion:
0.0932 A/pixel.
Very transparent blue sky. Temperature: about 30°C.
17 July 2022.





This second measurement confirms the results of the measurement made on July 12, 2022. This time there is a very small CWL offset (0.1 A) probably due a a different ambiant temperature.






Measurement in a f/7.3 beam

Optical set-up:
Sun => Takahashi TOA 150 mm => Edmund Optics 394-10 nm => Alluxa Ca K 1 A at normal incidence or tilted => Sol'Ex spectrograph with 10 micron × 4 mm slit. 125 mm f.l. collimating lens (re-focused on Ca K). Grating : 2400 l/mm. 125 mm f.l. imaging lens.
ASI290 camera. 12-bit acquisition. Dispersion:
0.0932 A/pixel.
Very transparent blue sky. Temperature: about 30°C.
17 July 2022.


The following three images show:
- the solar spectrum near Ca K and H (with the EO394-10nm filter),
- the spectrum transmitted by the Alluxa 1 A (normal incidence) and EO394-10 nm filters at f/7.3. Ca K3 is on the red wing of the bandpass of the filter (thin dark line).
- the spectrum transmitted by the Alluxa 1 A tilted at 9.2° and EO394-10 nm filters at f/7.3. As expected, the bandpass broadens and the CWL drifted to the blue.









Because of the low f-ratio and the large tilt, the filter profile losses its symetry while the FWHM increases significantly:



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