Measuring very low optical powers with a common camera

Abstract

We introduce a procedure to calibrate an inexpensive, commercial camera for optical power measurements. This allows the use of the camera as a very sensitive optical power meter that is able to measure powers down to the femtowatt level. A windowing technique, based on the selection of a region of interest from the total sensor area, is used to maintain a good signal-to-noise ratio over a large range of the measured optical powers. The increase of the exposure time of the camera shifts its detection limit to lower powers. Using this calibration procedure and the windowing technique, we measured 25 fW of optical power with a common complementary metal-oxide-semiconductor camera.

Ultrafast Third-Order Nonlinear Optical Response Excited by fs Laser Pulses at 1550 nm in GaN Crystals

“…The very low average power (~pW) of the TH beam generated in non-phase-matching conditions was measured using a common CMOS camera (Thorlabs, DCC1545M), without objective, as a power-meter, following a calibration method introduced by us and briefly described below [35]. The photosensitive array of the camera used by us (6656 µm * 5325 µm) consists of 1280 px * 1024 px, with the pixel size of 5.2 µm.…”

“…The CMOS camera is connected to a computer that acquires the images of the TH beam spot, generated at different incident intensities of the FH beam. The average power of the TH beam is computed by processing these images, following a method recently introduced by us for the use of a common camera as an ultrasensitive power-meter [35].…”

“…The method used for the measurement of very low optical powers using a common camera as a very sensitive power-meter is described in detail elsewhere [35]. Here, we will mention briefly the principle and several advantages of this method.…”

“…The measurement of the optical power with a camera is based on the fact that each pixel of the camera's photosensitive array can be considered as a power-meter of micrometric size that generates an electric signal proportional to the incident optical signal in the linear operation regime. By cumulating the response of all pixels and using a calibration procedure developed by us, the incident optical power can be measured down to extremely weak (fW) light levels, as was demonstrated in [35].…”

“…In this paper, the ultrafast third-order optical nonlinearity of c-plane GaN crystal, excited by ultrashort (fs) high-repetition-rate laser pulses at 1550 nm wavelength, is investigated for the first time by optical THG in non-phase-matching conditions and the corresponding third-order nonlinear optical susceptibility is determined. The very low average power of the third harmonic beam generated in GaN (~pW) is measured by image processing, following a method recently introduced by us for the use of a common camera as an ultrasensitive power-meter [35,36].…”