# Presentation: 481431

## Near Infrared SystemR&D Phase

**Gregory Tarl****é**
**University of Michigan**
**July 9, 2002**

## Outline

- NIR Science Objectives
- NIR System Concept
- Technical Challenges
- R&D Issues
- R&D Activities
- R&D Plan
- Deliverables
- Milestones
- Schedule
- Manpower
- Equipment
- Management
- Summary

## NIR Science Objectives

- At high redshift, restframe B and V have shifted beyond the sensitivity of CCDs, well into the NIR.
- NIR observations are essential:
- to distinguish among dark energy models (see talk by E. Linder)
- expand the science reach (see talk by T. McKay)
- provide _all_ photometry above z = 1.2
- provide trigger for high-z SNe
- NIR observations will identify the redshift of all SNAP galaxies as an integral part of the program. When a SN explodes, knowledge of host galaxy redshift will be used to eliminate contamination from much more numerous and less luminous type II SNe.
- reduce systematic errors

- Primary SNAP science goal: determine the expansion history of our universe out to redshift z = 1.7 to cover both the acceleration and deceleration epochs.

## NIR Observations Control Systematic Errors

-  **Gray Dust**
-  Restframe B and V measurements provide a good constraint on the impact of ordinary dust, yet may not provide sufficient information to constrain “gray” dust.
-  NIR observations extend the wavelength range over which each supernova will be imaged by 50%, providing a better chance to constrain non-standard models of dust.
-  **SN Evolution**
-  Progenitor characteristics may have a greater impact on the B light curve than on V or R. Measurement of V-R as well as B-V will provide a cross-check on this important systematic. NIR will provide restframe R observations out to z = 1.4.
-  **SN Magnification**
-  Tails on the intensity distribution of SNe at high redshift will signify the impact of lensing on apparent brightness.  NIR photometry allows measurement of restframe V out to z = 1.7.

**Notes:**
Truly grey dust is undetectable by color measurement, but physically motivated models of dust are actually only ‘greyer’ dust; they still affect light of different wavelengths differently.

## NIR System Concept

**NIR System Concept**

**150 NIR Megapixels:**
- 36 (2k  2k) 18 m HgCdTe detectors (0.34 sq. deg)
- 3 special bandpass filters covering 1.0 –1.7 m in NIR
- T = 140K (to limit dark current)

- HgCdTe

## NIR System: Performance Goals

| Field of View | ~ 0.3 square degrees | match CCD FoV to observe
every SN in every color |
| --- | --- | --- |
| Plate Scale
 | 0.17 arcsec / pixel | to achieve photometric accuracy with at most 2x2 dithering |
| Detector Type Wavelength Coverage | 2k x 2k H2RG HgCdTe
0.9 m - 1.7 m | HgCdTe device with 1.7 m cut-off allows passive thermal control |
| Read Noise 
Dark Current | 5 e- (multiple samples?)
< 0.1 e-/pixel/sec | Assures that photometry is zodiacal light limited |
| Quantum Efficiency
(Detector) | > 60% | to achieve adequate S/N to study SNe at z = 1.7 within time constraints |
| Filters | three special filters | to obtain redshifted ‘B’-band steps from 1 to 1. 7 m |

**Notes:**
various moments of the pixel response function spec (

## Technical Challenges

- Establish read-out strategy within time constraints with manageable readout noise (can we achieve 5 e- with a Fowler-4 read?), power and data volume (see NIR breakout talk).
- Obtain ~1% relative systematic photometric accuracy in under-sampled regime.
- Develop plan for testing and characterization of large numbers of HgCdTe detectors.
- Demonstrate that a prototype NIR detector can meet all SNAP NIR science driven requirements.

|  | WFC3 | NGST | SNAP |
| --- | --- | --- | --- |
| technology | Hawaii-1R | Hawaii-2RG
Raytheon-290 | Hawaii-2RG |
| science grade flight devices | 1 | 20 | 36 |
| spares | 1 | 5 | 8 |
| total | 2 | 25 | 44 |

**Notes:**
size of Airy disk for IR relative to pixel in optical and NIR
data volume?

## Readout Strategy

**Readout Specifications**
**Sensitivity to high-z SN can be achieved with eight 200 second exposures (see talk by C. Bebek).**
**S/N can be increased by reading the detector many times (nominally 10e****-**** ******** 5e****-**** with a Fowler-4 read). **
**Photometry errors can be reduced by dithering (2 ********2 dithering requires 4 ******** reads).**
**Baseline Readout Strategy**
**8 NIR exposures per filter [4 dithers ******** 2 (NIR filter linear size is 2********CCD)].**
**20 second readout time (includes reset, 4 pre-exposure reads, 4 post-exposure reads).  Readout ******** 10% of 300 second exposure time.**
**Frame readout time for Hawaii 2RG multiplexer at 100 kHz and 32 outputs = 1.2 seconds.  Total readout time: 8 ******** 1.2 = 9.6 seconds.**
**Possible to save power and channel count by developing 16 channel readout electronics with total readout time of ~ 20 seconds.**
_**Laboratory demonstration of 5 e- read noise is an important objective of the NIR R&D program.**_

## Intrapixel Variations

**At ******** =1 ********m (worst case) the SNAP Nyquist sampling size is 5.4 ********m (3x undersampled).**
**Intrapixel variations can introduce significant photometry errors.  For a fractional sensitive Area (********) = ******** RdA/A ~ 0.9, errors in excess of ~3% are possible.**
**Intrapixel variation for PACE HgCdTe devices have been measured with ******** = ~ 0.8**
**Simulations show that a 2********2 dither pattern should reduce **_**this**_** component of the photometry error to **_**well**_** below 1%.**
**By controlling the growth process, MBE HgCdTe should have ******** closer to unity. **
_**Laboratory demonstration of adequate photometry precision with dithering is an important objective for the SNAP NIR R&D program.**_

- Airy disk for  =1 m (projected on 18 m pixel)

## NIR System Trade Studies

- Focal plane configurations considered (see talk by C. Bebek)
- Thinned vs. non-thinned devices
- All NIR vs. **CCD/NIR**,
- NIR from ground etc.
- Read noise
- Can 5 e- be achieved with 8 reads in 20 seconds?
- Explore parameter space of wavelength cutoff, read noise, dark current and read time.
- Intra-pixel Variations
- Dither (2  2 is baseline); Need to verify with a real device.
- Mapping (fall-back option)
- Explore thermal & mounting concepts.
- Fallback options for RSC sole-source; identify alternate vendors (Raytheon?) for multiplexer, detector.

## NIR System Main R&D Activities

- Establish facility for testing and characterizing NIR FPAs.
- Study read noise and ability to reduce it with multiple reads.
- Study intra-pixel variations and establish impact on accurate photometry.
- Develop mechanical and thermal concept for NIR imager in an integrated focal plane in concert with LBL thermal and mechanical engineering group.
- Develop plan for testing and qualifying large number of HgCdTe devices.
- Produce all deliverables.
- Realistic cost and schedule estimate for CDR.

## NIR System: R&D Deliverables

| Deliverables | Date |
| --- | --- |
| Draft NIR system science driven requirements | August 2003 |
| NIR system mechanical and thermal specifications document. | January 2004 |
| Plan for receiving and qualifying flight detectors | May 2004 |
| Integration and Test Plan. | May 2004 |
| NIR system interface control document. | May 2004 |
| NIR observation plan. | June 2004 |
| Science grade HgCdTe detector meeting all NIR science driven requirements. | June 2004 |
| SNAP HgCdTe FPA science grade specifications. | July 2004 |
| WBS, cost, schedule, and management plan for design, construction and operations phases. | July 2004 |

## NIR System: R&D Milestones

| Milestone | Date |
| --- | --- |
| HgCdTe evaluation facility debugged and operational | December 2002 |
| Noise measurements on H1RG multiplexer | February 2003 |
| Noise and intrapixel measurements on science grade H2RG detector | July 2003 |
| NIR Draft Requirements Review  | August 2003 |
| Preliminary “SNAP” HgCdTe science grade specifications  | September 2003 |
| Noise and intrapixel measurements on “SNAP” prototype science grade H2RG detector | January 2004 |
| Prototype demonstration:  HgCdTe + readout | May 2004 |

## NIR System R&D Schedule

## An Experienced Team

**Tarl****é (IRIS, EXAM, PBAR, SMILI, HEAT-e********, HEAT-pbar, HNC, MACRO, GEM, COSMOS, ATLAS, HNX)**
**McKay (CASA, FNAL-DSC, SDSS, ROTSE)**
**Schubnell (FREJUS, WHIPPLE, HEAT-pbar)**
**Tomasch (PBAR, SMILI, HEAT-e********, HEAT-pbar)**
**Levin (MACRO, COSMOS, ATLAS)**
**Figer (GRIM-IR Camera (APO), NIRSPEC (KECK-II), GEMINI (Lick), FLITECAM (SOFIA), NGST)**

## NIR System R&D Equipment

**Science Grade H2RG HgCdTe to be acquired in FY03 to begin studies of noise and intrapixel variations.**
**2 “SNAP” Science Grade H2RG HgCdTe (from separate runs) to be acquired in FY04 for HgCdTe trade studies. **
**Dewar and readout electronics.**
**Optical equipment and devices. **

## NIR System R&D Management

- Tarlé (NIR systems manager) is responsible for overseeing all R&D phase activities and maintaining cost and schedule.
- Experienced team has been assembled.
- Management objective: NIR requirements specification document that reflects all science requirements and trades.
- Interface with other related SNAP teams; engineering team, focal plane instrument team, mechanical and thermal design, electronics, software, and calibration groups.
- Have begun dialog with RSC (prospective vendor) and will work to identify alternate vendors/technologies.
- Track ongoing work on WFC3 (GSFC), NGST (STScI).
- Actively collaborate with technology consultants Don Figer (STScI, NGST Instr. Scientist) and Don Hall (U Hawaii, IfA).
- Planning for internal and external reviews.

## NIR System Summary

- NIR system is essential to achieve SNAP primary science goals and will greatly extend the science reach.
- NIR system will have the largest number of infrared detectors ever and thus presents unique challenges.
- HgCdTe focal plane arrays are a relatively new but rapidly developing technology.
- R&D phase will be used to mitigate risks in key detector technology areas such as noise, intrapixel variation and qualification testing.
- A team experienced in large projects in ground and space based instrumentation has been assembled to carry out the NIR R&D program.