Photothermal Common-path Interferometry absorptance test on a single surface (L-Scan + T-Scan + Time-Scan)

Use this bundle for:

• To distinguish between optic ‘s front-, back-, and bulk absorption (L-Scan);
• Characterize homogeneity of absorptance of one optical surface (T-Scan);
• Characterization of absorption changes in time at a single point (Time-Scan)
• To provide “typical” absorption specifications for catalogs;
• To optimize optic’s manufacturing processes;

Test description

Photothermal Common-path Interferometry (PCI) for low absorption measurements is based on a spatially resolved pump-probe technique: a low-power probe beam senses the heating effect of an absorbed pump beam. The probe beam interferes with itself and measures the phase shift of the wavefronts. During the standard 1D absorption test, absorption is measured at multiple sites along the transverse line (of max 3mm). The standard measurement pack includes three test procedures: Transverse scan (T-Scan); longitudinal scan (L-scan) through the depth of the transparent sample and Time-scan – absorption is monitored at one site for 10 minutes.

Longitudinal scan (L-scan) Absorption is measured in the direction parallel to the optical axis. This test is necessary to locate the surface of interest for further measurements. During this scan front-, back-, and bulk absorption of the optical element can be distinguished.	Transverse scan (T-scan) Absorption is measured for the surface of interest (typically S1) in the direction perpendicular to the optical axis. Overall sample absorption is defined as the median value of the T-scan test. This test shows homogeneity of the absorbing surface.	Time scan Absorption is measured at a single test site at the surface of interest for a prolonged period of time. Standard time scan is 10 min per single spot per test surface. This test shows if absorptance is dependent on time.

Known limitations and risks:

• Might depend on the intensity of pump beam (nonlinear absorbance).
• Testing is available only for known calibration of substrate materials (ask for availability).
• Does not characterize absorption homogeneity over a large area.Use 2D measurement instead. Contact us to learn more about this test.
• Measurement sensitivity <1ppm could be reached but not for all samples.
• Works best for plane-parallel surfaces.
• Absorption might change with irradiation time (initial 10 min time scan is provided as standard, use long-term test for full characterization of time-dependence).

Most popular test parameters with fast turnaround