[Basic Optics Skills] Adjustment of Transmission Grating Pulse Compressor

[Basic optical skills] Adjustment of transmission grating pulse compressor

In the compressor, the attitude adjustment of the grating pair is one of the key technologies.

Its three-dimensional parallelism directly determines the compressibility of the output pulse and the focusability of the output spot.

This article will introduce a method to effectively adjust the transmission grating pair.

1. Preparation of adjustment auxiliary tools

(1) Each grating is equipped with a three-dimensional adjustment frame (or equivalent three-dimensional adjustment device);

(2) Horizontal reticle;

(3) Infrared night vision device;

(4) White card (white paper is fine (￣▽￣)") to receive reflected/diffracted light.

Figure 1 Auxiliary tools: three-dimensional adjustment stand, horizontal reticle, night vision device

2. Adjustment steps

Figure 2 Grating posture definition diagram

1. Adjustment of the grating surface and grating line direction

In order to ultimately achieve the goal of two gratings being parallel,

first ensure that each grating surface is perpendicular to a certain reference plane,

Generally, choose an optical table surface, or use a reticle to determine a reference horizontal plane

The author of this article feels that the most convenient way is to use a reticle.

The reference light source can use a reticle or a laser to be compressed.

The continuous semiconductor light source can also be used for preliminary debugging.

(1) First, set the incident laser to be strictly collimated and incident on the grating plane.

This horizontal setting can use the horizontal line of the reticle.

(2) Inject the incident light onto the grating at a certain angle.

Make sure that the 0th-order reflected light and -1st-order diffracted light can be observed at the same time (if you use a red light reticle, which is usually not the designed wavelength of the grating coating, you can clearly observe the reflected light),

Use the pitch adjustment knob and the grating in-plane leveling knob to adjust the reflected light and -1st-order diffracted light to the same height as the incident light,

That is, α and β in the side view of Figure 2 are both 0°

This shows that the grating surface and the grating direction are perpendicular to the horizontal plane of the incident light (main plane).

If the reflected light is weak, you can use an infrared card or a night vision device.

To ensure accuracy, it is recommended to observe the return light height as far away as possible

(1) This step requires the horizontal line and plumb line of the reticle to be illuminated on the grating at the same time. On the basis of the first step, place a 0° reflector (silver mirror is usually used) in the direction of the -1 order diffracted light to adjust the -1 order light to return to the original path.

According to the principle of light reversibility, when the horizontal line and vertical line of the -1 order diffracted light of the returned light coincide with the incident light at the same time, the light returns to the original path.

(2) At this time, adjust the angle between the incident light and the grating by rotating the grating with the grating line direction as the axis,

Adjust the position and angle of the 0° reflector to ensure that the return light returns to its original path at the same time, so that the 0-order transmitted light of the returned light coincides with the 0-order reflected light of the incident light - that is, the reverse extension line of the -1 order diffracted light of the incident light coincides with the 0-order reflected light of the incident light.

This is the Littrow angle we need!

3. Adjustment of grating parallelism

Figure 3 Parallel adjustment of the grating pair in the compressor based on the Littrow angle

(1) Based on the above steps, ensure that the positions of the grating and grating G1 are not moved,

Then remove the 0-degree reflector and install the second grating G2, making G2 and G1 as parallel as possible.

(2) Install the 0-degree reflector behind G2 again, and adjust the light return path according to (1) in the second step.

Then adjust the horizontal rotation knob of G2 so that the vertical line of the 0-level transmitted light of G2 coincides with the 0-level reflected light of the incident light - that is, G1 and G2 are "parallel"

(Note: Since the pitch adjustment of G2 interferes with the 0-degree reflector pitch adjustment, the pitch angle of G2 and the in-plane parallelism are not determined at this time)

Move the reticle to a certain angle and position so that it avoids G1 and directly illuminates G2, and completes the pitch and in-plane horizontal adjustment of G2 according to step 1.

At this time, all adjustments to the parallelism of the transmission grating are completed.

Figure 4 The transmission grating compressor independently developed by Boliu Technology

The picture shows the compact high-stability transmission grating compressor independently developed by Boliu Technology. It can be customized according to the actual needs of customers. Welcome to consult!

At this point, all adjustments to the parallelism of the transmission grating are completed.

Figure 4 Transmission grating compressor independently developed by Wave Technology

As shown in the picture, the compact high-stability transmission grating compressor independently developed by Waveform Technology can be customized according to the actual needs of customers. Welcome to consult!