Lock-in CD is efficient but assumption-dependent.

HarmoniX CD is assumption Free.

Feature

Signal detection

Number of harmonics measured

Lock-in Amplifier CD

HarmoniX (FFT-based CD)

Analog phase-sensitive detection at a single frequency (e.g., 1f)

Full time-domain signal digitized — FFT separates all frequencies

CD extraction

Assumes CD is isolated at 1f

Extracts CD explicitly from frequency spectrum

LD / LB contamination

Can leak into CD channel if phase or alignment imperfect

Directly measurable and separable (e.g., 2f, other harmonics)

Artifact visibility

Hidden — appears as “good looking” CD

Visible — you see non-CD contributions

Typically 1 (or 2 with dual lock-in)

All simultaneously

Phase sensitivity

Critical — misphasing causes mixing of signals

Phase resolved digitally; less fragile

Information content

Limited

Rich (CD, LD, birefringence signatures all accessible)

Post-processing flexibility

Minimal (locked at acquisition)

High (re-analyze data after acquisition)

User assumption required

“1f = pure CD”

No assumption — components are separated empirically