Various Sample Mounting Configurations for Optical Access

This article explains the numerous options of illuminating and collecting light in the sample space of the Cryostation for the standard configuration of the sample mount and sample post, as shown in Figure 1. Montana Instruments has several other options for various optical access, including the Cryo-Optic Add-On and Low Working Distance Window Options.

Figure 1: This article pertains to using the configuration of the standard sample mount shown above

The standard Cryostation 50 & 100-class sample chambers have five windows for optical access, while the 200-class has eight windows for optical access. Each of these windows has an outer vacuum window and an inner radiation window for thermal efficiency. The system comes with window covers to prevent unwanted radiation from entering into windows that are not being used. The standard sample mount is an adjustable post that allows the sample to be adjusted horizontally or vertically. The user can set the position of the sample post, then reconfigure the sample space (Figure 2) and begin a cool down.

Figure 2: Exploded view of standard sample chamber

The standard windows included with the Cryostation are a fused silica substrate with an AR coating from 400-1000 nm. In the typical system these include 30mm radiation windows and 50mm vacuum windows. Any of these windows can be easily replaced by the user for another substrate material or anti-reflection coating. Various window sizes are also available, but this needs to be determined prior to receiving the system. See Housing Options for more details.

OVERVIEW OF STANDARD OPTIONS

The options covered are summarized in the table below.

Option Description
1
Numerical Aperture through Standard Side Windows
2
Sample at 45˚, Reflection or Scattering Experiments
3
Beamsplitter for Reflection or Scattering Experiments
4
Obtuse Angle Reflection Experiments
5
Transmission Experiments
6
Reflection Experiments from the Top Window

OPTION #1: NUMERICAL APERTURE THROUGH STANDARD SIDE WINDOWS

The acceptance angle of incoming light from the outer window to the sample, when 30mm radiation shield windows are used, is just over 30° (full angle). Using the adjustable sample mount, the sample may be positioned near any of the five cold windows for a full angle of just over 80°. Additionally, if the user needs to position the sample closer to the warm window, there is the option to not use the cold radiation window; however, the base temperature will increase by several degrees Kelvin. The full angle of acceptance in this case is 120°. Figure 3 shows these three examples, and the table below shows the specification for working distance. Figure 4 shows the #2 condition of the sample mount coming close to the cold window.

See Acceptance Angle Dimensions - 50mm.pdf for an overview of acceptance angles when 50mm windows are used.

Figure 3: Acceptance angles for various sample mount placement

Description Working Distance Full Angle
1 Sample centered
44.4mm
30°
2 Sample near cold window
14.8mm
80°
3 Sample near warm window, cold window removed
4mm
120°

Figure 4: Scenario of #2 - sample near cold window, working distance of 14.8mm, and full angle of acceptance 80°

OPTION #2: SAMPLE AT 45˚, REFLECTION OR SCATTERING EXPERIMENTS

The platform in the sample chamber has eight holes that allow the sample mount to be positioned in 45° increments around the sample chamber. If the sample is mounted at 45° to the windows, the input light can be sent through one window, and the reflected or scattered light can be collected from a window that is at 90° from the input beam. Advantages to this setup are that the input and output are at separate windows. A disadvantages to this setup is the sample is in the center of the sample chamber, so without lenses inside the chamber, it may be difficult to have a high collection efficiency of the signal off of the sample. However, users may replace windows with lenses, or add lenses into the sample space to achieve better collection.

Figure 5: Reflection experiment

OPTION #3: BEAMSPLITTER FOR REFLECTION OR SCATTERING EXPERIMENTS

The sample is aligned with the window of the input light. Light is sent to a beamsplitter which passes some light and reflects some light into the sample chamber. The scattered/reflected light comes back out the window and part of it passes through the beamsplitter to the detector.

Figure 6: Alternative reflection experiment, working distance of 44.4mm

OPTION #4: OBTUSE ANGLE REFLECTION EXPERIMENTS

With the sample holder mounted almost flush with the sample mount, the input light can be brought in from the side window at a large angle, reflect off of the sample, and the output light collected from the window 180° from the input.

Figure 7: Large angle reflection

OPTION #5: TRANSMISSION EXPERIMENTS

With the sample mounted to the bottom of the sample mount, transmission experiments can be conducted. As in option #4, light is input from one side and is collected at the window 180° from the input. Montana Instruments also offers custom sample mounts that allow for transmission.

Note that for both option #4 and #5, the configuration will only work in the windows specified in the drawing with an extended chamber. In the non-extended system, there is not enough room between the vacuum jacket that houses the cold head and the back window to include an optic. If a user needs access through the back window, an extended version of the Cryostation is recommended.

Figure 8: Transmission experiment

OPTION #6: REFLECTION EXPERIMENTS FROM THE TOP WINDOW

Most often users utilize the top window or the side window (option #1) to configure their setup. If a user sets up a periscope they can gain optical access through the top window with a long working distance objective. If the user would like a closer working distance, Montana Instruments offers several low working distance options, which work best from the top window. The user can mount the sample on the top of the sample post, and Montana Instruments also offers various sample mounts if the user incorporates positioners or other options.

Figure 9: Reflection experiment through top window.

OTHER OPTIONS

There are other options for mounting samples in the Cryostation, including the Cryo-Optic Add-On, which places a vacuum compatible objective lens inside the vacuum space (working distance of 0.31-4.0mm depending on lens used). If the objective remains external there is a low working distance option, which allows the user to either place an objective 1-2mm from the sample or about 4mm from the sample. Montana Instruments also offers a variety of custom sample mounts and extended sample chambers to allow higher numerical apertures. Please contact our engineers for custom data collection requirements.