Green:  445 nm to 599 nm
Red:     598 nm to 869 nm

Yes, described in final inspection report WS-PVC3963-A.

Imaging Performance Goals for KPF Science

 KPF radial velocity science performance may benefit by considering these imaging optimization goals that mitigate unwanted perturbations to the PSF centroid location.

Goals for PSF symmetry

Goal: The shape of the PSFs across a single order should be symmetric about the center of the order

Cause: Pupil variations may cause the centroid to shift differently for each wavelengths PSF. If there is PSF symmetry about an orders’s center, then the average shift of all spots across an order will be minimized because spots will shift in opposite directions across the centerline

Goal for PSF similarity

Goal: The shape of the PSF within a single order should be similar.

Cause: Observed spectra will shift within an order at different observing epochs. If PSF similarity exists within an order, then a PSF’s centroid will appear consistent at different epochs.

Yes

Within Justificative Report they claim they meet these goals because they're using the prescription that KPF provided which was based on these goals, and that any asymmetries are generated in the spectrometer and not within the camera (seems reasonable)

The effective focal length in the x-direction (EFLX in Zemax) at the center of the field shall be 495 mm ± 0.25% (TBC), for both green and red cameras.

The effective focal length in the y-direction (EFLY in Zemax) at the center of the field shall be within 5mm of the EFLX value.

These values may be different from previous optical prescriptions of the cameras, when focal length may not have been well specified.            

Yes, described in final inspection report WS-PVC3963-A.

Yes, ICD pages are shown in camera final inspection report WS-PVC3963-A with majority of dimensions verified for as-built part.

Final WL mechanical model verified within KPF optical bench model.

Yes, met by design.

Winlight also vacuum-tested camera mechanical assembly before installation of optics (Justificative Report said they would do this at 90C)

The Camera Unit shall be designed using materials to provide thermal compensation so that optical performance over the specified thermal operation range will be satisfied.

Lenses must use densified coatings or equivalent to ensure satisfaction of operational vacuum and humidity requirement. Magnesium Fluoride coatings may not be used on the Field Lens due to the potential of damage by condensation.

Yes.

Athermalization met by design.

Justificative report mentions use of densified coatings and avoidance of MgF2.  Emails about coatings describe densified coatings.

The Camera Unit Design shall allow for adjustment of the optical focus on the CCD sensor to compensate for as-built compensation within the Camera optics, as-built defocus errors in the spectrograph optics, and for variations in atmospheric operating and test conditions (sea-level, mountain-top, high vacuum).

The method of focal adjustment is to vary the axial positioning of the FLA-cryostat assembly with respect to the LBA. The focus adjustment shall use fixed spacers and not an adjusting mechanism and not require removing the cryostat from the Camera or exposing the camera internals to the outside environment.

The GMA shall be integrated with the LBA. They shall be relatively aligned to the nominal separations defined in the green and red camera optical prescriptions. The nominal separations may be updated slightly if the camera optical prescription changes, or if the KPF spectrometer prescription changes.

The alignment tolerances shall be within 0.2mm in x,y,z, and 0.05 degrees in pitch, yaw, and clocking.

Verification of the final separation may be done using mechanical measurements. Note that the provided grism contains a grating, and the grating substrate edges may not be parallel to the grating grooves, by up to 1 degree error. The prism grooves will be well aligned to the prism, therefore when the grism is aligned to its nominal clocking position (based on the grooves), the grating substrate may be clocked by up to 1 degree. The GMA mount must have sufficient clearance to accept this possible 1 degree error of the grating substrate. KPF will have knowledge of this angle error several months before the grism is delivered to Winlight.

Inspection

Description given in Winlight final report is "with respect to camera optical axis" which must be a typo as that is mechanically impossible.  Will ask Winlight.

If numbers given within final report are "with respect to nominal" (as I suspect) then they easily meet our alignment tolerances.

The Camera Unit Design shall allow for adjustment by the customer of the GMA with respect to the LBA, in pitch, yaw, and clocking directions.

The resolution of the adjustments shall be less than 0.03 degrees in pitch, yaw, and clocking. The range of the adjustments shall be at least ±0.4 degrees, in pitch, yaw, and clocking, with the ranges centered on the nominal angular position of the GMA as defined in the prescriptions.

The camera design shall minimize stray light propagation and scattering and exclude outside light. The outer edges of lenses, and any lens barrel and lens clamp surfaces that are visible to the focal surface shall be coated with low reflectivity and low scatter material having < 5% TIS that is compatible with adjacent materials and operating at clean high vacuum (Total Mass Loss (TML) < 1% and Collected Volatile Condensable Material (CVCM) < 0.1%).

Surface treatments shall not be hygroscopic, including any coatings to reduce stray light. An inorganic black anodization treatment is acceptable. Also, an appropriate high-temperature vacuum bake of anodized parts may be done before camera part assembly to remove sulfuric acid outgassing. A low outgassing paint is also acceptable, such as Aeroglaze Z306 with vacuum baking.

Baffle apertures should be considered (TBD) in the lens assembly to prevent direct scatter paths from barrel edges to the focal plane. Barrels and extended surfaces may also be grooved to prevent grazing surfaces for incident light.

The Camera Mechanical ICD shows the Lens Barrel assembly mounting interface requirements including the optical axis location, and the structural mounting scheme, a six-point kinematic interfaces to Zerodur shim stacks. The Grism location and interface specifications are shown in the Mechanical ICD.

The LBA shall be provided with protective covers for both input and output apertures.

Yes, ICD pages shown in WS-PVC3963-A report with majority of dimensions verified for as-built part.

Final WL mechanical model also verified within KPF optical bench model.

Justificative Report shows shipping cover designs.

Yes, ICD pages shown in WS-PVC3963-A final report with majority of dimensions verified for as-built part.

Final WL mechanical model also verified within KPF optical bench model.

Cryostat installation procedure not expected to require additional information from Winlight.

The camera optical performance requirements shall be met when the FLA is subject to vacuum and the CCD is operating at cryogenic temperatures.

The field lens is used during laboratory testing under a pressure difference from external atmospheric pressure on the lens barrel side to high vacuum (10-6 mbar) on the sensor cryostat side. The field lens may also be subject to internal pressurization during cryostat venting operations, not exceeding 1.33 atmospheres.

Consequently, the field lens assembly shall include high-vacuum sealing features to the cryostat and to the field lens and shall accommodate the possibility of internal overpressure. The FLA vacuum total vacuum seal leak rate shall not exceed 10-8 mbar liter sec-1 under 1 atm external pressure.

The field lens assembly shall be made with best practice for safe cryogenic vacuum or pressure operations and shall be verified by analysis or test to survive the pressure conditions. The lens shall not have any internally radiused steps unless approved by KPF, and all surfaces shall be polished or acid-etched.

The vacuum side of the field lens will be located at approximately 5 mm from the cryogenic CCD active face that operates at -110°C. Consequently, the field lens will operate substantially below ambient temperature.

The mounting surface to which the field lens assembly is attached will operate at a temperature shown in the environmental specifications.

The operational temperature or pressure-gradient environments shall not degrade the Camera Unit’s operational optical performance requirements.

Yes.

Vacuum leak rate tested, described in camera final report (WS-PVC3963-A).

Temperature gradient across field lens analyzed within the Justificative Report.

Stress within the field flattener lens shall be less than 4.44 MPa for long term loads (5 years). For analysis, assume load is 1 atmosphere of external pressure.

Stress within the field flattener lens shall be less than 5.55 MPa for short term loads (12 hours).

For analysis, assume load is 1.3 atmospheres of internal pressure.

Evaluate maximum tensile stress.

Yes.

Winlight checked this in their mechanical Justificative Report.

Chris Smith also did analysis on KPF side.

All specifications (throughput, imaging, etc.) must be met over the operational environmental range.

The cameras must still be able to perform to specifications when returned to operational ranges after being exposed to the survival environmental range. The throughput must meet specifications after being exposed to the operational environments for 10 years.

The camera unit as packed for shipment may be subject to shock, thermal and pressure conditions. The camera units shall be handled & shipped in such a way as to not exceed the specified survival environment.

The survival range may be modified to reflect expected shipping conditions.

Bonded lenses shall be subject to an analysis and test program for like materials, configuration and environmental conditions as expected for the Camera lens elements. Bonded lens assemblies shall be verified as environmentally sound by test using three temperature cycles through the survival temperature range at a slew rate of 10 C/hour, with each cycle including thermal soaks at the extreme temperature limits of no less than 12 hours.

Yes.

Justificative Report says these conditions taken into account throughout the various analysis.

They did not quote on a bonding test program, and did not undertake one, so last paragraph no longer applies.

WS-PVR1015-A.pdf

Green:  445 nm to 599 nm
Red:     598 nm to 869 nm

Green
Optical

Green:  showed measured curves and all OK.

Red:  showed measured curves for FS and OK

For other glasses only have theoretical curves, and not specific curves for each glass type, only for a range of indicies.

Analysis is clear and echelle direction spots look good.

Cross-dispersion OK; see slides "Camera spot sizes and cross-talk.pptx" from Feb 26th 2020 weekly meeting.

Imaging Performance Goals for KPF Science

 KPF radial velocity science performance may benefit by considering these imaging optimization goals that mitigate unwanted perturbations to the PSF centroid location.

Goals for PSF symmetry

Goal: The shape of the PSFs across a single order should be symmetric about the center of the order

Cause: Pupil variations may cause the centroid to shift differently for each wavelengths PSF. If there is PSF symmetry about an orders’s center, then the average shift of all spots across an order will be minimized because spots will shift in opposite directions across the centerline

Goal for PSF similarity

Goal: The shape of the PSF within a single order should be similar.

Cause: Observed spectra will shift within an order at different observing epochs. If PSF similarity exists within an order, then a PSF’s centroid will appear consistent at different epochs.

They claim they meet these goals because they're using the prescription that KPF provided which was based on these goals, and that any asymmetries are generated in the spectrometer and not within the camera (seems reasonable)

The effective focal length in the x-direction (EFLX in Zemax) at the center of the field shall be 495 mm ± 0.25% (TBC), for both green and red cameras.

The effective focal length in the y-direction (EFLY in Zemax) at the center of the field shall be within 5mm of the EFLX value.

These values may be different from previous optical prescriptions of the cameras, when focal length may not have been well specified.            

SG:  their justification list in the report is reasonable. 

Also, mech report calls out grism rotation bearings as vac compatible.

Haven't checked the SW assembly in detail yet to look for air pockets, or make sure all bolts are vented, etc.

SG:  Note green camera is 95.2 kg, red camera is 90 kg.

Difference might be due to L4 glass type:  Green L4 is 1.44x heavier than Red L4.

Clocking:  Worst off-plane angle for VPH gratings was 3.5 arcmin, much less than the 1 deg KOSI had given as a worst case (and the WL mount design allows for).  Therefore OK for clocking.

Yaw angle needs to be adjusted to +/- 1.25 deg based on ghost analyses.  Conveyed to WL on April 13 2020.

Do we need to angle front flat face on green grism mount for stray light?

The Camera Unit shall be designed using materials to provide thermal compensation so that optical performance over the specified thermal operation range will be satisfied.

Lenses must use densified coatings or equivalent to ensure satisfaction of operational vacuum and humidity requirement. Magnesium Fluoride coatings may not be used on the Field Lens due to the potential of damage by condensation.

They don't show analysis wrt to the thermal compensation part of the requirement.

SG will check that regardless in Zemax.

Coating part of this requirement seems OK.

The Camera Unit Design shall allow for adjustment of the optical focus on the CCD sensor to compensate for as-built compensation within the Camera optics, as-built defocus errors in the spectrograph optics, and for variations in atmospheric operating and test conditions (sea-level, mountain-top, high vacuum).

The method of focal adjustment is to vary the axial positioning of the FLA-cryostat assembly with respect to the LBA. The focus adjustment shall use fixed spacers and not an adjusting mechanism and not require removing the cryostat from the Camera or exposing the camera internals to the outside environment.

The GMA shall be integrated with the LBA. They shall be relatively aligned to the nominal separations defined in the green and red camera optical prescriptions. The nominal separations may be updated slightly if the camera optical prescription changes, or if the KPF spectrometer prescription changes.

The alignment tolerances shall be within 0.2mm in x,y,z, and 0.05 degrees in pitch, yaw, and clocking.

Verification of the final separation may be done using mechanical measurements. Note that the provided grism contains a grating, and the grating substrate edges may not be parallel to the grating grooves, by up to 1 degree error. The prism grooves will be well aligned to the prism, therefore when the grism is aligned to its nominal clocking position (based on the grooves), the grating substrate may be clocked by up to 1 degree. The GMA mount must have sufficient clearance to accept this possible 1 degree error of the grating substrate. KPF will have knowledge of this angle error several months before the grism is delivered to Winlight.

Seems OK.  The concerns of the last paragraph (the 1 degree clocking of the grating) are no longer a concern.

Note they have chosen PTFE (Teflon) pads to support the prism.  Likely we should change these to PEEK to avoid creep?

The Camera Unit Design shall allow for adjustment by the customer of the GMA with respect to the LBA, in pitch, yaw, and clocking directions.

The resolution of the adjustments shall be less than 0.03 degrees in pitch, yaw, and clocking. The range of the adjustments shall be at least ±0.4 degrees, in pitch, yaw, and clocking, with the ranges centered on the nominal angular position of the GMA as defined in the prescriptions.

All ranges > +/- 0.4 degrees.

Yaw angle needs to be adjusted to +/- 1.25 deg based on ghost analyses.  Conveyed to WL on April 13 2020.

Resolution on both clocking and pitch/yaw adjustments ~10x finer than we asked for here.

Note for WL:  min increment for clocking is 0.03 deg in DJD, 0.003 in mechanical document.  Which one is the typo?

The camera design shall minimize stray light propagation and scattering and exclude outside light. The outer edges of lenses, and any lens barrel and lens clamp surfaces that are visible to the focal surface shall be coated with low reflectivity and low scatter material having < 5% TIS that is compatible with adjacent materials and operating at clean high vacuum (Total Mass Loss (TML) < 1% and Collected Volatile Condensable Material (CVCM) < 0.1%).

Surface treatments shall not be hygroscopic, including any coatings to reduce stray light. An inorganic black anodization treatment is acceptable. Also, an appropriate high-temperature vacuum bake of anodized parts may be done before camera part assembly to remove sulfuric acid outgassing. A low outgassing paint is also acceptable, such as Aeroglaze Z306 with vacuum baking.

Baffle apertures should be considered (TBD) in the lens assembly to prevent direct scatter paths from barrel edges to the focal plane. Barrels and extended surfaces may also be grooved to prevent grazing surfaces for incident light.

TM: Their approach to blacken all surfaces and put threads on all cylinders meets our reqs.  They propose to not blacken outer edges of lenses, but their argument that the edges aren’t both visible to the focal surface and illuminated by input light is reasonable.

Likewise, their planned baffles do not entirely prevent direct paths between barrel surfaces and focal surface.  With analyzed and found two instances of barrel surfaces that are both visible to the focal surface and illuminated by input light from non-m=1 VPH orders.  We presented this to WL, and they agree to review these instances.

TM: Okay by process

Tim

The Camera Mechanical ICD shows the Lens Barrel assembly mounting interface requirements including the optical axis location, and the structural mounting scheme, a six-point kinematic interfaces to Zerodur shim stacks. The Grism location and interface specifications are shown in the Mechanical ICD.

The LBA shall be provided with protective covers for both input and output apertures.

The camera optical performance requirements shall be met when the FLA is subject to vacuum and the CCD is operating at cryogenic temperatures.

The field lens is used during laboratory testing under a pressure difference from external atmospheric pressure on the lens barrel side to high vacuum (10-6 mbar) on the sensor cryostat side. The field lens may also be subject to internal pressurization during cryostat venting operations, not exceeding 1.33 atmospheres.

Consequently, the field lens assembly shall include high-vacuum sealing features to the cryostat and to the field lens and shall accommodate the possibility of internal overpressure. The FLA vacuum total vacuum seal leak rate shall not exceed 10-8 mbar liter sec-1 under 1 atm external pressure.

The field lens assembly shall be made with best practice for safe cryogenic vacuum or pressure operations and shall be verified by analysis or test to survive the pressure conditions. The lens shall not have any internally radiused steps unless approved by KPF, and all surfaces shall be polished or acid-etched.

The vacuum side of the field lens will be located at approximately 5 mm from the cryogenic CCD active face that operates at -110°C. Consequently, the field lens will operate substantially below ambient temperature.

The mounting surface to which the field lens assembly is attached will operate at a temperature shown in the environmental specifications.

The operational temperature or pressure-gradient environments shall not degrade the Camera Unit’s operational optical performance requirements.

Stress within the field flattener lens shall be less than 4.44 MPa for long term loads (5 years). For analysis, assume load is 1 atmosphere of external pressure.

Stress within the field flattener lens shall be less than 5.55 MPa for short term loads (12 hours).

For analysis, assume load is 1.3 atmospheres of internal pressure.

Evaluate maximum tensile stress.

All specifications (throughput, imaging, etc.) must be met over the operational environmental range.

The cameras must still be able to perform to specifications when returned to operational ranges after being exposed to the survival environmental range. The throughput must meet specifications after being exposed to the operational environments for 10 years.

The camera unit as packed for shipment may be subject to shock, thermal and pressure conditions. The camera units shall be handled & shipped in such a way as to not exceed the specified survival environment.

The survival range may be modified to reflect expected shipping conditions.

Bonded lenses shall be subject to an analysis and test program for like materials, configuration and environmental conditions as expected for the Camera lens elements. Bonded lens assemblies shall be verified as environmentally sound by test using three temperature cycles through the survival temperature range at a slew rate of 10 C/hour, with each cycle including thermal soaks at the extreme temperature limits of no less than 12 hours.