Ted4015

Figure 3(a) illustrates a schematic of the experimental arrangement employed for LCS. The set-up consists of a sample cell and a reference cell mounted on a thermally insulating block. The areas just under the cells have air gaps to increase the thermal resistance further. The insulator sits on a copper thermal base which is in contact with a copper enclosure which surrounds the cells and the insulator. The copper enclosure has a slot through which laser light can enter the sample and reference cells. This whole arrangement is mounted inside a stainless steel chamber for better thermal stability. The temperature of the liquids inside the sample and reference cells are measured using Pt100 thin film thermometers mounted inside the cells. The leads are thermally grounded on the copper base whose temperature is kept constant using a thermoelectric cooler (TEC) controlled by a thermoelectric controller (TED4015, Thorlabs Inc.). Silicone pipes connected to the sample and reference cells are used to fill liquid inside the cells and for draining the liquids out. The different parts of the set-up are explained in detail below.

All electrical measurements were carried out using a Signatone probe station and an Agilent B1500A semiconductor parameter analyzer. Laser diodes (Osram PLP520-B1 for 520 nm, LPC-826 for 650 nm, Thorlabs L808P200 for 808 nm, and Thorlabs L980P010 for 980 nm) were mounted onto the probe station and focused onto the sample. The laser power was controller by a DC power supply (Keithley 2450 Sourcemeter) in current source mode and measured using an optical power meter (Thorlabs PM100D and S121C). The size of the laser beam spot was intentionally made large enough to cover the whole channel region (100 × 200 μm²) of the device. The laser beam was projected onto a white paper with printed 1 mm × 1 mm grids and captured with a CCD camera mounted on the microscope for estimating the beam size and calculating the laser intensity. For the temperature measurement, the samples were attached to a Peltier heater, whose temperature was precisely controlled by a temperature controller (Thorlabs TED4015).