Bartłomiej Graczykowski Research Group

Tandem Fabry-Perot High Contrast Interferometer (TFP-2 HC, JRS Scientific Instruments & Table Stable)

It is a 2^nd generation tandem two triple pass Fabry-Perot interferometer, originally developed by Sandercock [1]. We employ it to study inelastic light scattering from Brillouin spectra over an extended range of GHz frequency.

Main features:

• Contrast - 10¹⁵;
• Frequency range - 1500 GHz;
• Mirror distance - 0.1-50 mm;
• Depending on the wavelength (λ) of laser light wavevector (k) can vary in the range of k = 0 to 23 µm^-1;

References: [1] J. R. Sandercock, The design and use of a stabilized multipassed interferometer of high contrast ratio Proc. 2nd Int. ConJ on Light Scattering in Solids ed. M Balkanski (1971).

Lasers (532, 660, and 780 nm)

I. λ=532 nm is a solid state CW single mode green light laser. It has an output power of 300 mW and spectral linewidth of <10 MHz. More details can be found at [https://www.laserlabsource.com].

II. λ=660 nm is Torus solid state CW single mode red light Laser. It has an output power of 200 mW and bandwidth of the order of 1 GHz. More details can be search at [https://novantaphotonics.com].

III. λ=780 nm is Toptica femtosecond fiber Laser. It consist super compact cold laser head and software controlled system. The Laser can generate pulse of time duration > 130fs with a repetition rate of 10 mHz. More information can be found at [https://www.toptica.com].

In-situ high Pressure BLS setup

The high pressure setup consist of a custom made metallic chamber, gas bottles and gas compressor. The 3D Polystyrene (PS) colloidal crystal sample deposited on a clean glass slide is fixed in a cylindrical sample holder and placed inside the high pressure chamber. The gas is supplied to the chamber at the specific pressure condition before the BLS measurements. BLS measurements is performed in back scattering geometry. A CW laser of = 532 nm is used as the probing light source. The laser beam is directed towards the high pressure chamber using a polarized cube beam splitter (PSB103). Using an achromatic lens of 125 mm focal length, the laser beam passing through the chamber window is focused on the sample. The back scattered light is transmitted through the same polarized cube beam splitter allowing s and p (sp) cross polarization for the incident and scattered beam, respectively. This configuration suppresses the BLS signal occurring from the longitudinal acoustic phonons of the gas. Using a half wave plate the polarization is rotated to 90°, allowing s-polarized beam to pass to the detector. The scattered beam is directed to the tandem FPI (JRS opticals) using mirrors and lens to measure the acoustic modes of the PS nanoparticles.