introduction
In modern optical technology, pulsed lasers are widely used in fields such as material processing, medical imaging, and basic scientific research due to their ultra-short pulse width and high peak power. To optimize laser performance, pulse broadening and compression are important
In the key step, the optical system design involves many complex calculations such as dispersion amount, Littrow angle, grating spacing and size. Traditional manual calculations are not only time-consuming and labor-intensive, but also prone to errors, affecting design efficiency and accuracy.
To this end, Wave Technology has launched a series of professional scientific calculators, which are optimized for pulse stretching compression system design. These calculators cover key links such as dispersion calculation, Littrow angle measurement, grating spacing and size design.
section, simplifying the complex calculation process. With the intuitive interface and efficient calculation engine, users can quickly and accurately obtain the required parameters, significantly improving design efficiency and ensuring optimal system performance.
Considering the optical implementation method of pulse broadening and compression, it mainly involves the calculation of the following parts
1. Calculate the amount of dispersion that needs to be introduced based on the change in pulse width.
2. Calculate the Littrow angle based on the grating line density and wavelength. When the incident angle = Littrow angle, the diffraction efficiency is the highest.
3. Calculate the grating spacing based on the dispersion amount and incident angle.
4. Calculate the minimum size of the two gratings based on the incident angle and grating spacing.
Example:
Ti:sapphire laser with wavelength of 800nm, average power of 4W, single pulse energy of 50uJ, pulse width of about 200fs, and hope to broaden it to 100ps level
Use the scientific calculator:
1. Broadening of ultrashort laser pulses (click to jump to use):
Taking the incident laser pulse width (200fs) and the outgoing laser pulse width (100ps) as an example, calculate the dispersion amount. The required second-order dispersion amount is calculated to be 720W fs².
Taking the incident laser pulse width (200fs) and the outgoing laser pulse width (100ps) as an example, calculate the dispersion amount. calculate
The required second-order dispersion amount is 720W fs².
2. Calculation of the diffraction angle and Littrow angle of the grating (click to jump to use):
Graduation density (from product information), wavelength, calculation of Littrow angle (Littrow angle: refers to the angle between the propagation direction of a light wave and its direction between the first grating line and the last grating line when it passes through a grating unit with a given number.) Select a grating with a grating density of 1380 and a wavelength of 800nm, taking the incident angle of 30° as an example.
Graduation density (from product information), wavelength, calculated Littrow angle (Littrow angle: refers to when the light wave passes
When passing through a grating unit with a given number, its propagation direction is the same as that between the first grating line and the last
The angle between a raster line. )
Select a grating with a grating density of 1380 and a wavelength of 800nm. Take the incident angle of 30° as an example.
The Littrow angle is calculated to be about 33.5°.
The Littrow angle is calculated to be about 33.5°.
But when the incident angle is equal to the Littrow angle, the diffraction efficiency is highest when this angle is used as the incident angle.
But when the incident angle is equal to the Littrow angle, the diffraction efficiency is highest when this angle is used as the incident angle.
3. Temporal dispersion of grating to compressor (click to jump to use):
Use the second-order dispersion calculated in 1 and the angle of incidence calculated in 2.
Use the second-order dispersion calculated in 1 and the angle of incidence calculated in 2.
The required grating spacing is calculated to be about 1200mm.
4. Calculation of grating size in pulse compressor (click to jump to use):
Using the incident angle calculated in 2 and the grating spacing calculated in 3, the beam diameter is set to 3.5mm, the edge protection range is set to 2mm, and the wavelength range is set to 790-810nm.
Using the incident angle calculated in 2 and the grating spacing calculated in 3, the beam diameter is set to 3.5mm, and the edge protection range
Set to 2mm and the wavelength range to 790-810nm.
The calculation results are D1=8.2mm and D2=65.4mm.
The final selection of raster information is shown in the figure:
D1 corresponding grating model: Gitterwerk 1385_10x8_6.35_X1. Center wavelength Wavelength: 800nm2. Clear aperture: 10x8mm3. Period Grating Period: 725nm4. Grading line density Grating Period: 1379.3 l/mm5. Grating size Size: 12mm*10mm*6.35mm6. Incident polarization Pol.: TE (s-pol)7. Diffraction efficiency Measured Efficiency: ≥99.0%
D1 corresponds to grating
Model: Gitterwerk 1385_10x8_6.35_X
1.Central wavelength Wavelength: 800nm
2. Clear aperture: 10x8mm
3. Period Grating Period: 725nm
4. Grading line density Grating Period: 1379.3 l/mm
5. Grating size: 12mm*10mm*6.35mm
6. Incident polarization Pol.: TE (s-pol)
7. Measured Efficiency: ≥99.0%
D2 corresponding grating model: Gitterwerk 1385_128x13_3_H1. Center wavelength Wavelength: 800nm2. Clear aperture: 128x13mm3. Period Grating Period: 725nm4. Graduation line density Grating Period: 1379.3 l/mm5. Grating size Size: 130mm*15mm*3mm6. Incident polarization Pol.: TE (s-pol)7. Diffraction efficiency Measured Efficiency: ≥98.5%
D2 corresponds to grating
Model: Gitterwerk 1385_128x13_3_H
1.Central wavelength Wavelength: 800nm
2. Clear aperture: 128x13mm
3. Period Grating Period: 725nm
4. Grading line density Grating Period: 1379.3 l/mm
5. Grating size: 130mm*15mm*3mm
6. Incident polarization Pol.: TE (s-pol)
7. Measured Efficiency: ≥98.5%
How to use the calculator:
In order to ultimately achieve the goal of two gratings being parallel, it is first necessary to ensure that each grating surface is perpendicular to a certain reference plane. Generally, an optical table surface is selected, or a reticle is used to determine a reference horizontal plane. Author of this article
I think the most convenient thing is to use a marking instrument. The reference light source can use a reticle or a laser to be compressed, and a continuous semiconductor light source can also be used for preliminary debugging.
(1) First, set the incident laser to be strictly collimated and horizontally incident on the grating plane. For this horizontal setting, the horizontal line of the reticle can be used.
(2) Inject the incident light onto the grating at a certain angle to ensure that 0-order reflected light and -1-order diffracted light can be observed simultaneously (if a red light reticle is used, which is usually not the design wavelength of the grating coating, the reflection can be clearly observed
light), use the pitch adjustment knob and the grating in-plane leveling knob to adjust the reflected light and -1 order diffracted light to the same height as the incident light, that is, both α and β in the side view of Figure 2 are 0°. This shows that the grating surface and the grating line direction are both vertical.
on the horizontal plane (principal plane) of incident light. If the reflected light is weak, you can use infrared cards or night vision devices. To ensure accuracy, it is recommended to observe the return light height from as far away as possible.
Find the Littrow angle:
(1) This step requires irradiating the crosshairs of the reticle, namely the horizontal line and the plumb line, onto the grating at the same time. On the basis of the first step, place a 0° reflector (usually a silver mirror) in the direction of the -1 order diffracted light to separate the -1 order light.
Return to the original route. 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, it is ensured that the light returns to the original path.
(2) At this time, by rotating the grating with the grating marking direction as the axis, adjusting the angle between the incident light and the grating, and adjusting the position and angle of the 0° reflector, it is always ensured that the return light returns to the original path, so that the return light is of level 0
The transmitted light coincides with the 0th order reflected light of the incident light - that is, the reverse extension line of the -1st order diffracted light of the incident light coincides with the 0th order reflected light of the incident light. This is the Littrow angle we need!
Adjustment of grating to parallel:
Figure 3 Parallel adjustment of grating pairs based on Littrow angle in compressor
Figure 3 Parallel adjustment of grating pairs based on Littrow angle in compressor
(1) Based on the above steps, ensure that the position of the reticle and grating G1 does not move, 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 to return to its original path according to (1) in the second step. Then adjust the horizontal rotating knob of G2 so that the vertical line of the 0-level transmitted light of the G2 return light 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 pitch adjustment of the 0-degree mirror, the pitch angle and in-plane parallelism of G2 are not determined at this time). (3) 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 point, all adjustments to the parallelism of the transmission grating are completed.
(1) Based on the above steps, ensure that the position of the reticle and grating G1 does not move.
Then remove the 0 degree reflector and install the second grating G2, making G2 and G1 as close as possible
parallel.
(2) Install the 0-degree reflector behind G2 again, and follow (1) in the second step
Adjust the light to return to its original path. Then adjust the horizontal rotation knob of G2 so that G2 returns
The plumb line of the 0th order transmitted light of the light and the 0th order reflected light of the incident light coincides - that is, G1 and
G2 "parallel". (Note: Since the pitch adjustment of G2 is inconsistent with the pitch adjustment of the 0-degree mirror,
Involved, the pitch angle and in-plane parallelism of G2 are not yet determined at this time).
(3) Move the marking instrument to a certain angle and position so that it avoids G1 and directly illuminates G2
Go up and complete the pitch and in-plane level adjustment of G2 according to step 1. At this point, the penetration is completed
All adjustments to parallelism of the radiation grating.
If you find any problems or errors while using the calculator, please contact us in time and we will make corrections in time. In order to thank you for your trust and supervision, we have specially prepared a "supervision reward" for you, such as
If you have anything else you need to add, please feel free to contact us. We are very honored to be able to provide some convenience for your scientific research experience. The road to scientific research is long and difficult. I wish all experts and scholars success in their scientific research and early results!
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