LCOS-SLM characteristics

Surface accuracy

Definition

Surface accuracy is the degree of surface distortion in the effective pixel area (15.9 mm × 12.8 mm) of an LCOS-SLM. It is evaluated by the PV (peak to valley) value that is the difference (maximum displacement) between the highest surface and the lowest surface and also by the RMS variation in the surface distortion.

Measurement method

Using a phase modulation optical system as shown in the figure below where the polarization direction of the incident light is aligned with the orientation of the liquid crystal molecules, an interference fringe that occurs between the LCOS-SLM and the reference mirror is captured. That interference fringe is then Fourier-transformed to obtain the phase distribution to calculate the surface accuracy. A measurement example of the interference fringe and the calculated surface accuracy are also shown below. The surface accuracy shape shown at (b) indicates the phase difference in 8-bit gray levels from 0 to 255 for one wavelength. The phase modulation of LCOS-SLM differs depending on the wavelength, so the surface accuracy of each of our LCOS-SLM types is measured by using typical light source wavelengths and the evaluated results are listed below.

 

Measurement setup for surface accuracy

Measurement setup for surface accuracy

Measurement example of surface accuracy

Measurement example of surface accuracy

Measurement results

The table below shows the surface accuracy evaluation results for each of our LCOS-SLM types. The PV value and RMS value averaged over the calculated surface shape data are listed here. The software for our LOCS-SLM has a feature for correcting the surface shape and allows acquiring a PV value of λ/20 or less.

Evaluation results for surface accuracy (typical example of average values)

Type No.

Wide wavelength band type

Specific wavelength type

-01

-07

-08

-02

-03B

-05

-13

-16

Wavelength of light source (nm)

633

1064

1064

785

1064

407

532

532

PV value

1.8λ

1.7λ

1.3λ

3.1λ

2.3λ

3.0λ

3.2λ

2.0λ

RMS value

0.4λ

0.4λ

0.3λ

0.6λ

0.5λ

0.5λ

0.7λ

0.4λ

Type No.

High-power laser type

Laser metal processing type

-02L/-02R

-03BL/-03BR

-16L/-16R

-03CL/-03CR

Wavelength of light source (nm)

785

1064

532

1064

PV value

3.1λ

2.3λ

2.0λ

2.3λ

RMS value

0.6λ

0.5λ

0.4λ

0.5λ

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