Attachment 1 SOW_4K_Cryo_Free_Optical_Cryostat.docx

STATEMENT OF WORK

4 K Cryogen-free Optical Cryostat System

LAB REQUESTING SERVICE: Nanofabrication and Measurement Group, Microsystems and Nanotechnology Division, Physical Measurement Lab

Background:

The Microsystems and Nanotechnology Division (MND) within the National Institute of Standards and Technology’s (NIST) Physical Measurement Lab (PML) develops integrated microsystems by advancing the state of the art in nanofabrication, thereby enabling the transfer of NIST measurement technologies to the industrial, academic, and government communities. The MND’s Single Emitters Group performs cryogenic optical microscopy and spectroscopy measurements of single quantum emitters in chip-based photonic structures. A closed-cycle, cryogen‐free cryostat system that allows flexible, free-space optics-based as well as optical fiber-based optical access to the cold sample is required to further advance projects vital to the research goals of the laboratory. The optical measurements intended to be performed using the cryogen-free cryostat system include optical transmission and reflection spectroscopy of chip-scale photonic devices containing quantum emitters (such as quantum dots or organic dye molecules), micro-photoluminescence and time-correlated single-photon counting of single quantum emitters embedded in chip-based nanophotonic devices, and high resolution fluorescence microscopy of single quantum emitters in thin films and fabricated photonic devices.

We require a closed‐cycle, cryogen free cryostat using a variable flow helium compressor, liquid helium generation and recirculation, or equivalent cooling approach. Cooldown of the system shall be achievable in an automated fashion, with all control software included. The system shall have sufficient interior sample chamber space to accommodate at least one set of cryogenic nanopositioning stages, for coarse and fine positioning of an optical fiber-based probe with respect to a sample, as well as a fixed, compatible fixed sample mount. The system shall be able to reach a temperature of 4.0 K or lower at a sample in vacuum environment, sitting on top of nanopositioning stage stack or fixed sample mount, while maintaining good temperature and vibration stability. Positioning stages are NOT being requested in the purchase. The sample chamber shall allow simple integration into typical, table-top microscopy and optical spectroscopy setups. Optical access from the top of the sample chamber is needed for integration with existing photoluminescence spectroscopy setups, and fiber optic and electrical feedthroughs are also needed. Modular vacuum shrouds are required to allow free-space optics-based access to the sample through either an in-chamber, high numerical aperture microscope objective, or long working distance objectives external to the chamber. The in-chamber objective option is required to reduce optical aberrations allowing the highest resolution in microscopy-based measurements. The ex-chamber objective option is required to allow microscopic imaging of large devices with an optical system in which the objective may be spatially translated across the entire extent of the top cryostat window. The system shall have, for both shroud options, sufficiently low vibrations at the sample to allow stable and low-drift device probing with optical fibers, minimize resolution loss in microscopy-based measurements, and minimize instability and drift of free-space optical excitation and collected signals. The technical specifications for the cryostat and shroud design in the proposed solicitation are determined based on the experimental parameters that we envision measuring with such a system while allowing ease of operation.

Technical Requirements:

The system shall meet or exceed the technical specifications identified below. All items shall be new. Prototypes, first articles, demonstration models, used, refurbished or otherwise developmental systems, will not be considered for award.

1. System shall be a closed-cycle cryostat using a variable flow helium compressor, liquid helium generation and recirculation or equivalent cooling approach. The compressor shall be air-cooled. Both the cryo-cooler and the variable flow helium compressor including any vacuum pumps shall be included in the offered system.

2. The sample temperature shall reach 4.0 K or less, and the sample environment shall be vacuum, not Helium exchange gas.

3. Temperature fluctuations at the base plate shall be < 15 mK peak-to-peak.

4. The system shall reach 4.0 K at the sample in 4 hours or less from room temperature.

5. The base temperature hold time shall be of 30 days or more.

6. Vibration amplitude at the sample platform shall be <15 nm peak-to-peak.

7. The system shall feature a sample chamber that allows simple integration with typical optical measurement setups that are mounted on a standard, floated optical table. Single-molecule microscopy and spectroscopy experimental setups comprise elements that are mounted on a floated optical table, and a chamber that offers direct, line-of sight access to the sample facilitates integration with such elements.

8. The sample chamber shall allow direct optical access to the cold sample from a top optical window. Stronger consideration shall be given to systems that allow optical access from axial windows as well as the top window. While top window sample access is necessary for use with existing single emitter photoluminescence setups, access from axial windows allows more flexibility in integrating the system within other optical measurement setups planned for the future.

9. The helium compressor, electronic control unit and/or any vacuum pumps shall not sit on the same optical table where the sample chamber resides. Having no cryostat parts other than the sample chamber on an optical table maximizes the usable work-area on the optical table.

10. The vertical dimension of the cryostat shall not exceed 80 cm. The cryostat will be placed on an existing optical table that sits under an overhead equipment shelf. The available space between the top of the optical table and the bottom of the overhead shelf is of 90 mm. Stronger consideration shall be given to systems that feature lower vertical dimensions. Sufficient space must exist above the cryostat and below the overhead shelf to allow for eventual cryo-cooler head replacements without moving the cryostat on or from the optical table. In addition, because the laboratory in which the system will be placed has very limited space, there is a desire to use the remaining space above the cryostat for auxiliary optical setups.

11. The interior sample chamber (sample space) shall have a diameter of at least 75 mm but not larger than 100 mm. Exact dimensions of the sample chamber shall be reviewed with the end user after award of the contract but prior to beginning construction of the system.

12. The cryostat system shall include two interchangeable vacuum shrouds to meet the following specifications:

a) One vacuum shroud designed to allow ultra-low working distance such that the sample can be placed to within 5 mm from the bottom of the top window, thereby allowing access to the sample using external high numerical aperture, long working distance microscope objectives. The viewable area of the sample through the chamber and radiation shield windows shall be of 25 mm or more. The shroud design shall allow the microscope objective to be spatially translated across the entire extent of the top cryostat window while maintaining focus on the sample. This is required to ensure microscopic imaging of large chips, for which sample translation with an in-chamber nanopositioning stack is either undesirable (e.g., when performing endfire-type optical fiber testing), or insufficient for visualization of relevant portions of the sample and in-chamber probes.

b) One vacuum shroud designed to host one vacuum and low temperature compatible microscope objective with standard thread to perform microscopy and spectroscopy-based measurements though the top window. The objective shall sit vertically above the sample, inside the vacuum chamber. The objective integration should be such that there are no optical windows between the sample and the objective. A working distance of 5 mm or less shall be achievable.

Both vacuum shrouds shall include all the necessary parts for thermal connection to the cold-plate. Both shall be reconfigurable to allow supplemental pumping with an external pumping system.

13. Optical windows shall be mounted on the vacuum shrouds such that they can be exchanged and are interchangeable by the end user without affecting the system performance. The final design of each vacuum shroud including choice of the material for the optical windows, window thickness, anti-reflection coatings and wedge options shall be reviewed with the end user after award of the contract but prior to beginning construction of the system.

14. The temperature at the sample on top of the positioning stage stack shall be 4.0 K or lower for both shroud configurations, and the sample environment shall be vacuum, not exchange gas, at that temperature. Any thermal braids or other cooling mechanism required to achieve this temperature shall be included in the system. Phonon interactions between single emitters and their hosting media is a main factor impacting the indistinguishability of emitted single-photons. Because one of the main goals of the proposed research is on maximizing such indistinguishability, it is desirable to perform experiments at such sample temperatures.

15. Capability for cryogenic stage integration for free-space optics based device testing: While nanopositioning stages are not being requested at this time, there is a desire to integrate one existing nanopositioning stage stack in the sample space, for testing devices with an in-chamber microscope objective. For such purpose, the system shall be capable of housing in its sample space, with the in-chamber microscope objective shroud (item 11 b), one low temperature compatible motorized xyz positioning stage stack consisting of.

a. Two horizontal motion coarse positioners (Attocube Systems model ANPx101/LT/RES) with dimensions 25 mm x 25 mm x 12 mm in size.

b. One vertical coarse motion positioner (Attocube Systems model ANPz101/LT/RES) with dimensions 25 mm x 25 mm x 25 mm in size.

c. One high resolution xyz piezoelectric scanner (Attocube Systems model ANSxyz100/LT) with dimensions 25 mm x 25 mm x 12 mm in size.

The system shall have electrical feedthroughs for all electric connections necessary for operation of the xyz positioning stage stack.

16. Capability for cryogenic stage integration for optical fiber based device testing: While nanopositioning stages and a sample mount are not being requested at this time, there is a desire to integrate two nanopositioning stages and one sample mount simultaneously in the sample space, which will be purchased in the future, for testing devices with in-chamber optical fibers. For such purpose, the system shall be capable of housing in its sample space, with the ex-chamber microscope objective shroud (item 11 a), two low temperature compatible motorized xyz positioning stage stacks, and one fixed sample mount simultaneously, as specified below.

a) Each of the two motorized xyz positioning stacks consist of:

1. Two horizontal motion coarse positioners (Attocube Systems model ANPx101/LT/RES or equivalent), providing a minimum of 5 mm of linear (in-plane) translation in the x and y directions at 4 K.

2. One vertical coarse motion positioner (Attocube Systems model ANPz101/LT/RES or equivalent), providing a minimum of 5 mm of linear (out-of-plane) translation at 4 K.

b) The fixed sample mount shall allow placement of wafers of at least 5 mm x 5 mm horizontal dimensions in-between the two xyz positioning stacks. The sample shall be positioned to allow imaging of its top surface from the top cryostat window with an ex-chamber microscope objective (item 11 a) with working distance of 15 mm or less. At the same time, the space between the sample surface and the bottom of the innermost radiation shield shall be of 5 mm or more to clear the height of existing angled optical fiber holders, which will be mounted on top of the coarse positioner stacks.

The system shall have electrical feedthroughs for all electric connections necessary for operation of the xyz positioning stage stack

17. Integrated objective: One vacuum compatible microscope objective that can be integrated within the vacuum shroud and focus on a sample in the sample space is required. The microscope objective shall also meet the following requirements:

a) The numerical aperture of the objective shall be 0.75 or higher.

b) The objective shall be infinity-corrected

c) Transmission >80% in the 400 nm to 800 nm range.

The objective choice shall be reviewed with the end user after award of the contract but prior to beginning construction of the system

18. Fiber optic feedthrough allowing introduction of at least two 250 micrometer-jacketed optical fibers into the cryostat sample chamber shall be provided. Feedthrough shall consist of a 1/8” Swagelok tube fitting welded to the appropriate cryostat flange, or equivalent.

19. Feedthroughs allowing introduction of at least four high-frequency SMA lines into the sample space shall be provided.

20. A minimum of 25 free electrical connections shall be provided into the sample area. The wiring shall be heat sunk at < 4.0 K. These free electrical connections are meant for future introduction of temperature sensors, heaters, etc., and do not include the connections needed for the low temperature stages and standard sensors and heaters. These electrical connections shall be thermally lagged into the sample space. The electrical connections shall be

21. Sensors to measure the base temperature of the system (e.g., at the cold finger) and the temperature at the top of the sample positioning stack shall be provided and installed in the system. A temperature controller that enables measurements from the two sensors and control of the heater shall be provided.

22. The system shall allow control of the sample temperature with the following specifications:

a. The sample temperature shall be dynamically adjustable between 4 K or less and 100 K or more during cryostat operation.

b. Control of the sample temperature shall be achieved through a fast feedback loop, based on temperature measurements taken at the sample

c. The settling times for sample temperature tuning between any two values within the range of 4 K to 30 K shall be of five minutes or less. Stronger consideration shall be given to systems with the shortest sample temperature settling times. The ability to quickly reach a set temperature is required to minimize experimental drift, ensuring reliable temperature-dependent data.

d. The sample vertical position drift due to heating or cooling shall be of 60 microns or less over the entire operating range of 4 K to 350 K.

e. Stronger consideration shall be given to systems that allow control of static sample temperature and sample temperature ramps via software, through a provided user graphical interface as well as provided Matlab, Python and Labview scripts. The need to perform frequent, automated sample measurements at various temperatures is anticipated, requiring software control via scripts.

f. Stronger consideration shall be given to systems in which the sample temperature may be adjusted from a provided control software interface that can be operated through a remote connection. Experiments that will be run in the cryostat typically run continuously for several days, and require frequent monitoring of various parameters, in particular sample temperature. Having a control software that enables monitoring and control of all cryostat parameters via a remote computer connection is necessary to ensure that the sample conditions can be maintained over the course of the experiments.

23. Any vacuum pump(s) required in cooling the system to cryogenic temperatures shall be included. During standard operation, the system shall reach a base pressure of 1 x 10-5 torr or lower.

24. The helium compressor shall include >33 meters long flex lines such that the compressor can be placed in the service galley outside the main laboratory.

25. Control software

a. Cool-down and pump-out shall be fully automated and controlled via computer interface. The ability to control supplemental pumping systems shall be integrated into the standard software.

b. All required software for running the system shall be provided, including standalone software and Python LabView drivers. The software shall allow for temperature set-point control, temperature monitoring, and diagnostics of the vacuum pump-down and helium compressor. The control software should also allow control of the sample temperature independently from the base plate temperature.

c. Stronger consideration shall be given to systems that feature cryostat control software capable of running automated program scripts from MATLAB, LabVIEW, and Python for direct data acquisition of relevant cryostat parameters as a function of time, such as at least base plate and sample temperature, heater currents and chamber pressure. Experiments that will be run in the cryostat typically run continuously for several days, and require frequent monitoring of various parameters. The ability to track the sample temperature and other parameters as a function of time is necessary to ensure comprehensive knowledge of the sample measurement conditions.

d. Stronger consideration shall be given to systems that feature control software that accepts remote computer connections for both parameter viewing and cryostat control. Experiments that will be run in the cryostat typically run continuously for several days, and require frequent monitoring of various parameters, in particular sample temperature. Having a control software that enables monitoring and control of all cryostat parameters via a remote computer connection is necessary to ensure that the sample conditions cab be maintained over the course of the experiments.

Warranty:

Standard 1-year warranty is required. Options for extended warranties should be considered depending on price.

Inspection/Acceptance:

Inspection will be performed on-site, with imaging and free-space and optical fiber-based photoluminescence spectroscopy of known samples performed.

Packaging/Marking:

No special packaging is needed

Freight/Shipping Charges:

All shipping arrangements and costs are handled by the vendor. Shipping will be included in the system price.

Schedule (Required Delivery Date/Period of Performance):

Delivery shall be FOB Destination to NIST Gaithersburg Building 216/E102 and shall occur not later than twenty-four (24) weeks ARO

Payment Schedule The Contractor shall be paid, in accordance with Net 30-day payment terms, upon receipt and acceptance of a proper invoice, in accordance with the following schedule:

NOTE: Partial shipments and partial invoices will not be accepted, unless other-wise requested and accepted by the Contracting Officer prior to award offer. Proposed payment schedules shall be submitted with vendor’s response to the RFQ for consideration