Holmarc’s surface Plasmon resonance Apparatus Model: HO-ED-P-10 is designed for the creation of surface Plasmon wave at resonance angle. This model consists of gold coated prism with high refractive index & He-Ne ‘p’ polarized laser source with spatial filter assembly. This model is called as Kretschmann configuration model. With its new and integrated design, this device is easier to setup and operate so that students can easily understand its principles and theories.
In this apparatus Goniometer kept at 0-180 degree for easy of operation & reflection from prism points to the laser at 0/180 degree for zero degree reflection angle measurement. Spatial filter assembly with 45X objective is used for SPR setup. Lens assembly make parallel beam & refocus the laser at the backside of gold coated prism. The rectangular dark image in enlarged beam can be scanned with photo detector within a specific range of angles using Goniometer stage. The resolution of Goniometer is 1 arc min. A nonlinear curve with a dip in the curve noted for certain angular scanning with the help of pinhole photo detector. Half wave plate is used for change p & s polarized state of He-Ne laser. Thereby we can observe dark band disappear & then come again in an interval of 90 degrees.
Demonstrate the experiment to see the dark band in the reflected beam from the gold coated prism.
Note the angle of absorption occurred using photo detector.
Study the change in polarization from p to s using half wave plate.
As we know gold metal consists of bulk of free electrons and they have electric field called as evascent wave or surface wave. These oscillating coherent wave moves in longitudinal direction with propagation k vector. In mean time the 632.8nm laser with p polarized state have its own electric field. At an angle greater than critical angle for total internal reflection this electric field interlock or coupled with surface wave produced by gold metal at Au-Air (dielectric) interface. This is called resonance condition. At this resonance condition there is a loss of energy hw & loss of momentum hk occurs in the optical electric field which will lead to the loss / absorption in light. This will clearly see as rectangular dark band in enlarged view of reflection light from gold coated prism. One of the important applications in SPR; is the analysis of change happened in a dielectric medium while it used on the top of the prism. As an example by using protein molecules, one can analysis the change in molecular binding energy level by analyzing shift in the absorption band.
Entire apparatus set up on an optical bread board
Gold coated Prism
Spatial Filter Assembly