RESUMEN
In this paper, a 1064 nm pulsed laser source and a short-wave IR (SWIR) camera are used to measure the total system efficiency associated with a digital holography system in the off-axis image plane recording geometry. At a zero path-length difference between the signal and reference pulses, the measured total system efficiency (15.9%) is consistent with that previously obtained with a 532 nm continuous-wave laser source and a visible camera [Appl. Opt.58, G19 (2019)APOPAI0003-693510.1364/AO.58.000G19]. In addition, as a function of the temporal delay between the signal and reference pulses, the total system efficiency is accurately characterized by a component efficiency, which is formulated from the ambiguity function. Even with multimode behavior from the pulsed laser source and substantial dark current noise from the SWIR camera, the system performance is accurately characterized by the resulting ambiguity efficiency.
RESUMEN
In this paper, we achieve the shot-noise limit using straightforward image-post-processing techniques with experimental multi-shot digital holography data (i.e., off-axis data composed of multiple noise and speckle realizations). First, we quantify the effects of frame subtraction (of the mean reference-only frame and the mean signal-only frame from the digital-hologram frames), which boosts the signal-to-noise ratio (SNR) of the baseline dataset with a gain of 2.4 dB. Next, we quantify the effects of frame averaging, both with and without the frame subtraction. We show that even though the frame averaging boosts the SNR by itself, the frame subtraction and the stability of the digital-hologram fringes are necessary to achieve the shot-noise limit. Overall, we boost the SNR of the baseline dataset with a gain of 8.1 dB, which is the gain needed to achieve the shot-noise limit.
RESUMEN
Using wave-optics simulations, this paper defines what subaperture sampling effectively means for digital-holography applications involving atmospheric turbulence. Throughout, we consider the on-axis phase shifting recording geometry (PSRG) and off-axis PSRG, both with the effects of sensor noise. The results ultimately show that (1) insufficient subaperture sampling manifests as an efficiency loss that limits the achievable signal-to-noise ratio and field-estimated Strehl ratio; (2) digital-holography applications involving atmospheric turbulence require at least three focal-plane array (FPA) pixels per Fried coherence length to meet the Maréchal criterion; and (3) off-axis PSRG is a valid and efficient implementation with minor losses, as compared to on-axis PSRG. Such results will inform future research efforts on how to efficiently use the available FPA pixels.
RESUMEN
In this paper, we study the use of digital holography in the on-axis phase-shifting recording geometry for the purposes of deep-turbulence wavefront sensing. In particular, we develop closed-form expressions for the field-estimated Strehl ratio and signal-to-noise ratio for three separate phase-shifting strategies-the four-, three-, and two-step methods. These closed-form expressions compare favorably with our detailed wave-optics simulations, which propagate a point-source beacon through deep-turbulence conditions, model digital holography with noise, and calculate the Monte Carlo averages associated with increasing turbulence strengths and decreasing focal-plane array sampling. Overall, the results show the four-step method is the most efficient phase-shifting strategy and deep-turbulence conditions only degrade performance with respect to insufficient focal-plane array sampling and low signal-to-noise ratios. The results also show the strong reference beam from the local oscillator provided by digital holography greatly improves performance by tens of decibels when compared with the self-referencing interferometer.
RESUMEN
In this paper, we use digital holography (DH) in the off-axis image plane recording geometry with a 532 nm continuous-wave laser to measure the system efficiencies (multiplicative losses) associated with a closed-form expression for the signal-to-noise ratio (SNR). Measurements of the mixing efficiency (36.8%) and the reference noise efficiency (74.5%) provide an expected total system efficiency of 22.7%±6.5% and a measured total system efficiency of 21.1%±6.3%. These total noise efficiencies do not include our measurements of the signal noise efficiency (3%-100%), which are highly dependent on the signal strength and become significant for SNRs>100. Thus, the results confirm that the mixing efficiency is generally the dominant multiplicative loss with respect to the DH system under test; however, excess reference and signal noise are significant multiplicative losses as well. Previous results also agree with these experimental findings.