an in situ optical specimen holder is disclosed which may be utilized for imaging and analysis during dynamic experimentation . this holder assembly includes a set of focusing and reflection optics along with an environmental cell . electromagnetic radiation can be used to optically excite the specimen in the presence or absence of fluid . a highly reflective mirror may be used to focus the radiation on to the specimen without the presence of any heating components within the cell . the spot size of the irradiation at the specimen surface can be varied , thus exciting only a specific region on the specimen . the window type cell provides a variable fluid path length ranging from the specimen thickness to 500 μm . the holder has the provision to continuously circulate fluids over the specimen . the pressure within the cell can be regulated by controlling the flow rate of the fluids and the speed of the pumps .