Next Generation Space Telescope (NGST)

Technology Demonstration Instrument

**Rapid Infrared-Visible**

**Multi-Object Spectrograph**

**(RIVMOS)**

**Lens Statement of Work (SOW) and Specification Document**

Statement of Work (SOW) for the Visible and Infrared Lenses for the
Rapid Infrared-Visible Multi-Object Spectrograph.

V060302

## 1. SCOPE AND INTRODUCTION

This Statement of Work (SOW) establishes the requirements for the
fabrication and testing of the ten (10) optical, infrared lenses, the
design and analysis of cryogenic lens barrel mounts, and the assembly,
alignment and testing of the lens assemblies for the Rapid
Infrared-Visible Multi-Object Spectrograph (RIVMOS) instrument as
described herein. The ten lenses are part of the optical train for the
Rapid Infrared-Visible Multi-Object Spectrograph (RIVMOS) instrument, a
ground based demonstration instrument for the Next Generation Space
Telescope's (NGST)'s micro-shutter MEMS technology. The specifications
described herein are based on requirements driven by the instrument's
optical design operating in the wavelengths of **0.6 to 5.5 microns**.
The collimating lens assembly (containing lenses 1-3) shall operate at a
temperature of **90 Kelvin**, and the camera and pupil imager lens
assemblies (containing lenses 4-8 and 9-10, respectively) shall operate
at a temperature of **25 K**.

This procurement is for the fabrication of the ten (10) individual
lenses as described in this SOW and on the individual lens drawings.
This procurement shall also be for the design, analysis, and fabrication
of three (3) lens barrel mounts meeting the herein stated requirements,
and also the lenses mounted and aligned in the lens barrel mounts. This
procurement shall also cover the entire test data required as specified
in section 9. As a substitute for cryogenic test data, the vendor shall
provide detailed analysis data as proof that the lens barrel assemblies
shall not distort the lenses and shall hold the lenses in their required
positions within the specified tolerances at cryogenic operational
temperatures. GSFC shall cryogenically test the lens subassemblies as
described in section 9.1 upon receipt of the lens assemblies for
acceptance testing. The vendor shall supply the safe, protective
shipping containers for the lens assemblies. The three lens assemblies
named briefly here are the collimating lens group (3 lenses, namely
Lenses 1-3), the cameral lens group (5 lenses, namely Lenses 4-8), and
the pupil imager lens group (2 lenses, namely Lenses 9 and 10). The
deliverable items for this contract are specified in section 15.

## 2. QUOTATION REQUIREMENTS

Quotation and technical proposal for the lenses and lens assemblies
shall be itemized for each lens and shall indicate the extent to which
the specifications will be met. Also, in the quotation, when applicable,
the specifications that are driving the price shall be noted and
possible alternatives should be provided for consideration. Exceptions
to specifications shall be indicated. Exceptions will be considered on a
case-by-case, lens-by-lens basis. The bid should also include a separate
quote on a spare set of lenses (lenses only, unmounted) which shall
include ten (10) lenses, one of each lens type (L1-L10), which shall
also meet the specifications detailed in this document and on the lens
drawings.

1.  **Mount drawings from vendor**

Upon acceptance of bid, vendor shall provide GSFC with mechanical
drawings of proposed barrel mounts and mounting scheme within three
weeks of acceptance. These drawings shall be subject to approval by
GSFC.

## 3. APPLICABLE DOCUMENTATION

### The following drawings are provided for the purpose of procurement. 

###  **Individual Lens Drawings**

### There is a separate drawing for each lens with its associated tolerances. They are labeled by lens name (i.e., Lens 1) as well as a drawing number (i.e., GA 2057090-GA 2057099). The lens drawings contain all of the required dimensional, tolerance, and performance specifications/requirements such as surface irregularity, center thickness, clear aperture and wedge, as well as the lens substrate. **All radii and dimensions are specified at 293 K**. The vendor shall meet these specifications at ambient temperature and document via analysis of the ambient data any degradation which shall occur at the respective assembly operating temperatures as described in section 5. Special notes are below: 

**3.1.1** Radii of curvature: test plate fit. Please indicate the
closest test plate radii of curvature you have for each surface of the
lens. The radii of each lens should be matched within one fringe to test
plates that have an absolute accuracy to within 0.1 %.

**3.1.2** Size of the lenses: see spec \"clear aperture\"

**3.1.3** Flat bevels can be modified or suppressed. The bevels on the
drawings are illustrative and may be modified by the vendor as needed.

**3.1.4** Protective bevels can be added

**3.1.5** Please let us know if any of the tolerances are unreasonable
for your capabilities.

**3.2 Lens Assembly Drawings**

### There are also lens group drawings for each of the 3 lens groups (collimator, camera, and pupil imager) labeled drawings 2057088, 2057089, and 2057116, which specify the lens spacings. Airspace, decenter, and tilt of each lens are also listed on each drawing. All specifications shall be met at ambient temperature. The vendor shall verify that no degradation shall occur at the operational temperature, with the exception of the lens despacing as described in section 5. Specifications are in inches unless otherwise noted. Only the clear aperture diameters for the lenses are required and not the Outer Diameter (OD) or edge diameter as the vendor will design and fabricate the mount to meet the overall spec for the clear aperture. The OD required will depend on the individual mechanical mount design. Therefore, for the lens barrel mount design and fabrication, the clear aperture should be the only diameter requirement. The vendor is free to oversize the lenses as needed, provided the lenses fit in the overall envelope constraints as detailed in section 3.3. The mounting scheme illustrated in the lens assembly drawings may be modified by the vendor provided it does not violate the outer envelope or mounting restraints, such as size and placement of boltholes to mount the assemblies to the RIVMOS instrument. These modifications will be subject to approval by GSFC as stated in section 2.1.

The lenses will be mounted in three barrels:

1\) Collimator assembly (lenses 1, 2, 3)

2\) Camera assembly (lenses 4, 5, 6, 7, 8)

3\) Pupil imager assembly (lenses 9, 10)

**3.3 Special physical constraints on the lens group mounts**

The outer envelope dimensions of the individual subassemblies are listed
on the lens assembly drawings. The lenses shall not be oversized to the
extent that the lenses and the barrel mounts will not meet this
constraint.

4.  **Special note**

If there is a discrepancy between specifications stated in this SOW
document and the specifications stated on the drawings, the drawings
shall take precedence.

### Again, quotation and technical proposals for the lenses for the two different options shall be itemized for each lens and should indicate the extent to which the specifications will be met. 

## 4. IN-BAND TRANSMITTANCE 

The required minimum peak transmittance is 97% for each lens between 0.6
µm and 5.5 µm. If this is unachievable, the vendor shall provide
recommendations as to what in-band transmittances are possible for each
of the three given lens substrates: LiF, ZnSe, and BaF2. The vendor
shall specify in their bid which substrates shall be coated to achieve
the minimum peak transmittance requirement. Transmission curves for the
coated and uncoated substrates shall also be provided in the bid, with
cost and performance for each option noted.

## 5. OPERATIONAL TEMPERATURE 

The collimating lenses shall meet the optical performance requirements
(as specified on each individual lens drawings, as well as tilt and
decenter on the subassembly drawings) at their operational temperature
of **90 K** when mounted as per the subassembly requirements on the
drawings described in section 3.2**.** The camera and pupil imager
lenses shall meet the optical performance requirements (as specified on
each individual lens drawings, as well as tilt and decenter on the
subassembly drawings) at their operational temperature of **25 K** when
mounted as per the subassembly requirements on the drawings described in
section 3.2**.** It is assumed that no degradation of these
specifications will occur at cryogenic temperatures when mounted;
therefore the vendor shall verify that the lenses meet these
specifications at cryogenic temperatures by testing them at ambient
temperature and verifying through analysis of the ambient data that
degradation shall not occur when mounted and at the operating
temperatures. If there is expected degradation of these specifications,
which includes surface figure error of either side of the individual
lenses, in going from 293 K to 90 K and 293 K to 25 K for the respective
lenses when mounted in the assemblies, the vendor shall quantify so in
their bid. The vendor shall also provide analysis of such degradation,
including how much degradation shall occur, as part of the deliverable
data as specified in section 10. The vendor shall meet the despace
requirements as listed on the subassembly drawings at ambient
temperature and provide analysis as part of the deliverable data to show
the expected lens despace at each subassembly's respective operational
temperature. The airspace between lenses has already been compensated to
reflect the predicted expansion in going from cryogenic to ambient
temperatures.

## 6. OPTICAL LENS QUALITY

1.  **Temperature Effects on Coating**

The coating shall show no signs of visible deterioration following the
temperature cycling from 293 K to 90 K and 25 K, respectively. The
transmission curve shall also not deteriorate with such temperature
cycling. The vendor shall guarantee this based on past performance of
such coatings.

2.  **Index of Refraction**

The vendor shall provide substrates with the following index of
refraction requirements. The vendor shall provide GSFC with actual
indices of refraction of these three substrates to within 0.0005 for
these wavelengths and temperature in their bid.

These indices of refraction are specified at 293K, with a pressure of 1
atm. The tolerance is +/-0.0010 for all materials.

**Table 1. Indices of refraction at 293 K (+/-0.0010)**

        
0.6um           0.8um           1.5um           2.4um           3.5um           4.5um

LiF     
1.3918          1.3889          1.3832          1.3744          1.3587          1.3387

BaF2    
1.4741          1.4704          1.4662          1.4633          1.4590          1.4540

ZnSe    
2.6141          2.5241          2.4572          2.4417          2.4351          2.4313

3.  **Scratch/dig**

The scratch/dig requirement is 60/40 for each of the lens substrates.

**6.5 Transmitted Wavefront Quality**

The vendor shall provide lenses which meet the following transmitted
wavefront quality requirements at ambient temperature as listed in table
2.

**Table 2. Transmitted wavefront quality data at 293 K**

[Group beam diameter at lens numerical aperture (NA) transmitted
wavefront error]{.underline}

collimator 18 mm at L1 0.055 0.045 waves RMS

camera 13 mm at L8 0.11 0.070 waves RMS

pupil imager 3.05 mm at L9 0.06 0.032 waves RMS

Interferometric testing shall be performed on each of the lens
subassembly to verify that it meets the minimum ambient wavefront error
specifications. This data shall be delivered with the lenses as stated
in section 9. A schematic of the test setup to be performed by the
vendor is illustrated in Figure 1, below.

![](media/image1.wmf)

**Figure 1. Wavefront error test setup.**

These tests shall be performed with a point source from an
interferometer centered with respect to the mechanical axis of the
assembly such that a collimated beam exits the other end. A reference
mirror is in collimated space at the opposite end of the assembly from
the point source. For the collimator assembly, the point source is on
the L1 side of the assembly, approximately 160 mm from the vertex of L1.
There is a collimated beam exiting L3. For the camera assembly, the
point source is on the L8 side of the assembly, approximately 59 mm from
the vertex of L8. There is a collimated beam exiting L4. For the pupil
imager assembly, the point source is on the L9 side of the assembly,
approximately 25.3 mm from the vertex of L9. There is a collimated beam
exiting L10.

## ENVIRONMENTAL REQUIREMENTS

The vendor shall deliver lenses that meet the following environmental
requirements. The vendor shall verify these requirements through
similarity and past performance only.

**For Collimating Lens Group:**

Acceptance Test Environment

\- Temperature: 293 1 K and 90 K ± 1 K

\- Humidity: \< 40% RH

Storage Environment

\- Temperature: operating temperature to +40C

\- Humidity: \< 40% RH

Operating Environment

\- Operating temperature: 90 K

\- Pressure: \< 10^-6^ Torr

##  For Camera and Pupil Imager Lens Group:

Acceptance Test Environment

\- Temperature: 293 1 K and 25 K ± 1 K

\- Humidity: \< 40% RH

Storage Environment

\- Temperature: operating temperature to +40C

\- Humidity: \< 40% RH

Operating Environment

\- Operating temperature: 25 K

\- Pressure: \< 10^-6^ Torr

## 8. FABRICATION AND MOUNTING REQUIREMENTS

1.  **Mount/Barrel Fabrication Special Constraint Requirements**

**8.1.1** The front and back ends/surfaces of the collimator
barrel/mount assembly shall have an optical reference surface that shall
be polished flat to 1 wavelength PV at 0.633 microns measuring
wavelength. This reference surface shall have a minimum area of 0.25
square inches and be perpendicular to the mechanical axis of the barrel
mount to within 15 seconds. The location of this reference surface may
be set by the vendor subject to approval by GSFC. The front and back
ends/surfaces of the barrel/mount of the pupil imager and camera
assemblies shall be polished flat to 1 wavelength PV at 0.633 microns
measuring wavelength.

**8.1.2** There shall be three alignment fiducials scribed on each of
the barrel mounts: one on each end to align decenter and one on the side
to align despace as shown in the mechanical drawings. The vendor shall
measure and report knowledge of the end (decenter) fiducials with
respect to the mechanical axis to an accuracy of 0.001 inches. The
vendor shall measure and report knowledge of the side (despace)
fiducials with respect to the mechanical axis and the vertex of each of
the end lenses to an accuracy of 0.001 inches. Each fiducial shall have
a width that shall not to exceed 0.003 inches and a depth that shall not
exceed 0.005 inches. The minimum length of the fiducial is 0.25 inches
long. The fiducials shall be scribed on a surface that has a surface
roughness that is not to exceed 16 microns. The decenter fiducials can
be on the optical reference surfaces as described in 8.1.1. The
positions of the decenter fiducials, as well as the despace fiducial on
the collimator lens assembly are arbitrary and may be set by vendor
subject to GSFC approval.

3.  There shall be a vent hole between each lens as shown in the
    assembly drawings to allow for outgassing in a vacuum. There shall
    be no unvented airspaces in the mouting subassemblies.

4.  There shall be three mounting holes on the ends of the barrel mounts
    as shown in the mechanical drawings to allow a test flat to be
    mounted to the assembly during the testing phase at NASA/GSFC.

**8.1.6** The inside of the barrel shall be coated with a coating that
is absorptive in the IR. Absorption curves for the coating over the
bandpass shall be included in the data. This coating shall be optimized
for performance at the specified wavelength range of 0.6 m to 5.5 m and
shall not chip or peel during cryogenic cycling.

**8.2 Mounting Requirements of the Lenses in the Barrel/Mount**

Tilt, decenter, and despacing requirements and their associated
tolerances for the lenses in the assemblies are listed on the individual
lens assembly drawings.

## 9. REQUIRED TESTING AND VERIFICATION

## 9.1 Required Lens Testing 

The vendor shall be responsible for carrying out any lens or materials
tests, analysis and verification by similarity necessary to assure
conformity to the requirements. A checklist of all tests performed and
records obtained shall be delivered to GSFC along with the lenses.
Records of all tests shall be maintained and copies of all test data
shall be deliverables.

GSFC requires that the vendor shall carry out the following tests and
provide test data as deliverables on each delivered lens prior to being
assembled in the mounts. These tests shall include the following:

-   Radius of curvature measurements, such as a fringe photo of surfaces
    against a test plate, to within 0.1 % at ambient

-   Transmitted wavefront error for each subassembly at ambient as
    described in section 6.5

-   Scratch/dig test at ambient

-   Spectral transmittance scans for each lens

    2.  **Required Verification**

The vendor shall also verify the following items.

-   Lens dimensions (outer diameter, edge and center thickness, etc.) to
    within 25 microns.

```{=html}
<!-- -->
```
-   Incoming and Outgoing Visual inspection of substrates, surface
    polish, and coatings

-   Lens name and S/N

-   Measurement of fiducial positions on subassemblies as described in
    section 8.1.2

-   Verification of coating performance as specified in section 6.1

-   Verification of lens performance within environmental conditions as
    described in section 7

-   Review of delivered documentation and check lists

## DATA AND ANALYSIS

**10.1 Data**

All lens data, sketches, and images shall identify lenses by its unique
identification and surface coating. The required data products are as
follows:

**Data on all required testing and verification stated above in Section
9**

Data shall be provided on all requirements stated above in Section 9. In
addition, the vendor shall provide the following data:

**Spectral transmittance scans for each lens**

Relative spectral transmittance scans shall be supplied for each coated
witness sample at ambient temperature as listed in section 9.1. The
scans should span 0.6 to 5.5 m for in-band transmittance. Vendor shall
also provide an absolute transmittance scan for each coated witness
sample at ambient temperature for at least one wavelength in the
bandpass. A sketch shall be supplied to show what portion of the lens or
witness sample was measured. The scans must be supplied in both hardcopy
and electronic format. Electronic data files must be in ASCII or
Microsoft Excel (.xls) format. Electronic files may also be mailed
electronically to the cognizant engineer or offered as a download from
an accessible FTP or HTML web site.

**Transmission curve for all three substrates**

Vendor shall also provide in their bid a transmission curve from 0.6 to
5.5 m for all ZnSe and BaF2 substrates with and without coating, for all
coating options as described in section 4.

**Data on Indices of refraction for the three substrates used**

The vendor shall provide in their bid data on the indices of refraction
of LiF, BaF2, ZnSe at ambient for the wavelengths listed in Table 1 as
specified in section 6.2.

**Proposed mounting scheme**

Upon acceptance of the bid, the vendor shall provide mechanical drawings
of the proposed mounting scheme as described in section 2.1.

**Wavefront image of lens blank**

Vendor shall provide a transmitted wavefront image of the polished lens
blank, showing homogeneity of the individual substrates, as well as any
documentation provided by the material supplier. Alternate documentation
of homogeneity will be considered.

**Notes on cleaning, storage and required operational environment**

This includes any special instructions on cleaning, storage, and minimum
required operational environment over a specified maximum time duration
to maintain lens quality at optimal bandpass transmittance performance.

**Out-going inspection notes**

Sketches or photographs indicating any visible features (scratches or
marks) observed during outgoing inspection.

**Absorption curves of the barrel housing interior coating**

Vendor shall provide an absorption curve showing the absorptive
characteristics over the bandpass of the coating to be used on the
interior of the barrel housing.

**Specification checklist**

The checklist shall include a list of all of the tests performed to show
conformity to requirements, as well as data obtained from those tests,
including interferograms of both sides of each of the individual lenses
showing surface irregularity. Dates, initials of test engineers,
records, and filenames shall also be included on the checklist.

**Mechanical drawings of actual lens assembly barrel mounts**

The vendor shall also supply GSFC with mechanical drawings of the actual
lens barrel mounts designed and fabricated for the lens assemblies.

**Documentation of lens assembly mounts**

The vendor shall also supply documentation showing lens barrel mounts
meet required subassembly specifications as set forth on the subassembly
drawings 2057088, 2057089 and 2057116.

2.  **Analysis**

In addition, the cryogenic performance of the lenses shall be verified
via the following analyses:

**Analysis of cryogenic performance**

The vendor shall verify through analysis of the ambient data that the
mounting design provided by the vendor shall meet the specifications set
forth in this document at the respective temperatures of 90 K for the
collimator assembly and 25 K for the camera and pupil imager assembly.
As a substitute for cryogenic test data, the vendor shall provide
detailed analysis data as proof that the lens barrel assemblies shall
not distort the lenses and shall hold the lenses in their required
positions within the specified tolerances at cryogenic operational
temperatures, with the exception of the lens despacing, which shall be
met at ambient and analyzed to show cryogenic despacing. Vendor shall
also document any expected degradation of the surface figure error,
tilt, and decenter for the individual lenses when mounted and operating
at their respective cryogenic temperatures.

**Spectral bandpass performance at 90 K and 25 K, respectively
(calculated from ambient lens spectral transmittance scans)**

The vendor shall also verify through analysis of the ambient spectral
transmittance scans of the lenses as described in sections 9.1 and 10.1
the spectral bandpass performance of the lenses at 90 K for the
collimator lenses and 25 K for the camera and pupil imager lenses.

## 11. LENS LABELING AND LENS BARREL/SUBASSEMBLY LABELING 

Each delivered lens shall be uniquely marked outside the clear aperture
with an identifying part number consisting of its descriptive lens name,
i.e., collimating lens #1, camera lens #4, pupil imager lens #9, etc.
Distinguishable abbreviations for these are also acceptable, i.e., Coll
L1, Cam L4, PI L9, etc. Each lens subassembly shall be uniquely marked
on the outside of the mount. There shall be a mark on the collimator
lens barrel at the approximate position of L3 labeled "L3". There shall
be a mark on the camera lens barrel at the approximate position of L8
labeled "L8". There shall be a mark on the pupil imager lens barrel at
the approximate position of L10 Labeled "L10". These marks will be used
to identify which end of the barrel mount points toward the detector.

## 12. WITNESS SAMPLES AND THEIR LABELING

Two (2) optical witness samples for each lens shall be supplied. These
witness samples shall be from the same substrate as its associated lens,
and whose coatings were formed during the same evaporation run as the
lens. Each witness sample shall be polished flat with a general optical
finish and be representative of the transmission quality of its
respective lens. Witness sample packages shall be marked as per the
instrument lens and with identifying letters (e.g. "L1-001" and "L1-002"
for witness samples for lens 1). The optical witness samples shall be
circular with 25.4 0.5 mm outer diameter.

## 13. ANOMALY REPORTING AND CORRECTIVE ACTION

The contractor shall notify GSFC of any manufacturing failures or
anomalies within 24 hours. The contractor shall contact and consult with
the GSFC cognizant engineer in order to plan and authorize corrective
action.

## 14. SHIPPING

The contractor shall assure that the lenses are adequately secure within
the containers to prevent damage during shipping. Package and sealing
methods shall prevent exposure of the optical surface to residuals from
out-gassing materials and excessive humidity. Any fixturing must not
contact critical surfaces. Instructions shall be affixed to the exterior
of shipment attesting to the delicate nature of the contents and
necessity of inspection by personnel familiar with the technical
characteristics of the contents.

## 15. DELIVERABLES

The following are the required deliverables:

1.  Lenses: Ten (10) lenses that meet the required tolerances and
    specifications as stated in this SOW and on the drawings

2.  Three (3) lens barrel/mounts: Design, analysis, and fabrication of
    three lens barrel mounts with associated restrictions and
    fabrication tolerances as stated in this SOW and on the drawings

3.  Lens subassemblies: Three (3) lens subassemblies with the lenses
    listed as deliverable item 1 aligned and mounted to the barrel
    mounts listed as deliverable item 2 to within specified required
    tolerances

4.  Witness samples: Twenty (20) witness samples, as defined in Section
    12

5.  Data as defined in Sections 9 and 10.

GSFC will accept partial delivery. Partial delivery is defined as one or
more completed lens assembly, together with its corresponding witness
samples and associated data and test results as specified in sections 9
and 10.

16. **GSFC INSPECTION**

GSFC shall have the right to visit the vendor to monitor progress and/or
view the testing of the optics. GSFC shall be notified two weeks prior
to coating of the optics in the event that the cognizant engineer should
wish to inspect the lenses prior to continuation of the work. GSFC shall
have the right to visit the vendor to monitor progress and/or view the
testing of the optics as well as the mounting scheme, provided notice
that is acceptable to both parties is made prior to the visit.

## 17. NASA/GSFC ACCEPTANCE TESTING

GSFC shall carry out acceptance tests on each delivered lens assembly.
These tests may include the following:

-   Sub-system transmitted wavefront error for each lens group at .633
    µm wavelength, ambient and cold

-   Sub-system throughput over the bandpass 0.6 µm to 5.5 µm at ambient
    and cold

-   Sub-system focal length, ambient and cold

18. **EVALUATION CRITERIA**

Award will be made to the lowest priced, technically available vendor,
using the following evaluation factors weighted in order of importance:

## Meeting the requirements---Most important

The vendor shall demonstrate through testing, analysis, and data as
described in sections 9 and 10 that the three lens assemblies meet the
herein stated requirements at their operational temperatures of 90 K for
the collimator optics and 25 K for the camera and pupil imager optics.

## Past performance in delivering similar systems

The vendor must provide at least 3 references for similar cryogenic
lenses being quoted and delivered within the past year if vendor wishes
to be considered based on past performance. Include Company Name, Phone
Number, Contact and Order Number or approximate delivery schedule.

## Delivery schedule

Vendor shall give a delivery schedule for each of the lens assemblies
and their associated data in their bid.

Final Payment shall be made after installation of the optical assemblies
and testing has been completed and demonstration that the system meets
or exceeds the requirements.