# All-Optical Method of Determining Laser Power from the Photomechanical Effect
## 2 Materials and Methods  
The patterned PDMS elastomers were fabricated from Sylgard 184 which uses a 10:1 mix ratio for the base and curing agent. A 5 mL volume of base was first added to a 20 mL vial. The diazo chromophore, Oil red O, was mixed into the base yielding a concentration of 0.5 wt.% followed by agitation. The curing agent was then added to the base and rigorously mixed. Bubble formation occured after mixing so the vial was covered with Parafilm(r) and small holes were poked through the surface. The vial was placed in a vacuum concentrator for 5 min until the bubbles were removed from the mixture.  
A diffraction grating was written on the surface of a PDMS elastomer in a similar manner as that described in References [100,101]. The burnable DVD was first split and the exposed surface relief grating was cleaned of any dye with 70% ethanol. Two spacers were placed on the grating surface with their long axis perpendicular to the diffraction grating groove direction as illustrated in Figure 1. The dye, base, and curing agent mixture was poured onto the grating surface between the two spacers. The mixture was then blade coated to uniform thickness by dragging a trovel over the two spacers. The blade-coated fluid was immediately transferred to an oven and cured at 80 \({}^{\circ}\)C for two hours, which resulted in a 550 um-thick elastomeric film. An atomic force microscope (AFM) was used to confirm the quality of the surface-relief grating, where an image from one of the samples is shown in Figure 1d.  
The cured sample was cut into a circular piece with a tail from which it was hung. The hanger and sample were enclosed in a polycarbonate box. The box was surrounded with foam insulation except in two locations. One polycarbonate window allowed the pump and probe beams to pass through the box. The other window was covered by a bandpass filter to block any residual 532 nm pump light while transmitting the diffracted 650 nm probe beam. A linear CCD array (TCD1501C [102]) with a \(\sim\)7 um width per pixel was placed outside the box and oriented perpendicular to the incident probe beam's direction of propagation. The diffracted probe beam had an initial length of \(\sim\)10.5 cm as measured from the sample to the linear CCD array.  
Temperature measurements were performed by placing a thermistor and heating element inside the box and connecting them to a thermostat. To create a stable temperature inside the box that could be reasonably adjusted with a thermostat, the initial temperature was raised a few degrees above the laboratory room's temperature. The angle of the diffracted probe beam was recorded by the linear CCD array in 1.5 \({}^{\circ}\)C increments.  
For pump power measurements, the pump and probe lasers were aligned so that both beam spots were centered on the same location over the surface of the film. Figure 1e shows images of the pump and probe laser spots and topological profiles after Weiner noise filtering. Both the 532 nm pump and 650 nm probe beams were in operation for more than 10 min prior to any experimentation so that they could reach a temperature equilibrium and stabilize the output power. The pump beam was passed through a variable density filter to control the pump power. Infrared light with a wavelength of 1064 nm was removed from the pump beam with a KG-1 filter. Shutters were used to toggle the pump and probe beams on/off. As shown in Figure 1b, a beam splitter sent some of the pump to a reference detector and let the rest of the beam pass through to the polycarbonate window and illuminate the dye-doped PDMS sample.