CN1306334C - Miniaturization pulse stretcher design method for compensating high material dispersion of regenerative amplifier - Google Patents

Abstract

The present invention discloses a design method which is suitable for a miniaturized femtosecond laser impulse stretcher used in a regenerative amplifier with high material chromatic dispersion compensation and belongs to the femtosecond pulse amplifying technique. According to the relationship among the phase phi of a stretcher, the position S1 of an optical grating and the curvature radius R of a spherical lens, the method adopts a concave spherical lens, a convex spherical lens, an optical grating and a plane lens for structural design. The present invention is characterized in that when the curvature radius of the concave spherical lens is R, the distance S1 between the optical grating and the concave spherical lens moves between O and R to be determined; the convex spherical lens and the optical grating are overlapped up and down; and if the stretching optical spectrum of incident light at this time, is wider than the lens surface of the concave spherical lens, the curvature radii of the concave spherical lens and the convex spherical lens need to be reduced with equal proportion so as to reduce the degree of the stretched optical spectrum and keep the original stretching quantity. The design method has the advantages of easy operation for straightening a light path, small spatial chromatic dispersion and compact structure. The stretcher can contain more material chromatic dispersion in an amplifier. The dimension of the stretcher is one third of the dimension of a traditional Offner stretcher and one half of the dimension of a Martinez type stretcher.

Description

Miniaturized Pulse Stretcher Compensating for High Material Dispersion in Regenerative Amplifiers

technical field

The invention relates to a miniaturized pulse stretcher for compensating the high material dispersion of a regenerative amplifier, which belongs to femtosecond pulse amplification technology.

Background technique

In order to amplify the femtosecond laser pulse, it is necessary to first broaden the seed pulse from the oscillator to the nanosecond level, then amplify it, and finally compress it to the width of the incident pulse, while having an energy increment of more than a million times. The principle behind compressing the pulse back to the same magnitude as the incident pulse is that if the dispersion of the additional material in the amplifier cannot be fully compensated by other means, then it is necessary to design pulse stretchers and compressors that match its material dispersion. Usually, the structure of the grating-to-compressor has no other method to arbitrarily change its dispersion characteristics except for the grating spacing and incident angle. In order to change the sign of the dispersion, the stretcher is a combination of a grating pair and a spherical mirror. Calculations prove that the aberration of the spherical mirror for non-paraxial rays can be converted into dispersion. This dispersion, together with variations in the grating-to-grating spacing and angle of incidence in the compressor, can be used to compensate for material dispersion in the amplifier [1]. Nevertheless, neither the usual stretchers of the Matinez type [2] nor the Offner type [3] can handle large material dispersions (such as those in regenerative amplifiers). Generally speaking, because the Martinez-type stretcher has a larger aberration than the Offner-type stretcher, this aberration can be converted into additional dispersion. Therefore, under the same condition of the compressor structure, the Martinez Type stretchers can accommodate more material dispersion and are more suitable for regenerative amplifiers, while Offner type stretchers are generally considered unsuitable for use in regenerative amplifiers.

[1] Zhigang Zhang et al., Appl., Opt., Vol.36 No.15(1997) 3393.

[2]O.E.Martinez, IEEE J.Quantum Electron., Vol.23 No.1(1987)59.

[3] G. Cheriaux et al., Opt. Lett., Vol.21 No.6 (1996) 414.

Contents of the invention

The object of the present invention is to provide a miniaturized femtosecond laser pulse stretcher for compensating the high material dispersion of the regenerative amplifier. The femtosecond pulse stretcher is used for compensating the dispersion of the regenerative amplifier, and has the characteristics of large dispersion of the containing material, small size and simple structure.

Since the Offner type stretcher adopts the concentric arrangement of concave and convex spherical mirrors, it is recognized as an aberration-free stretcher (when the two gratings are respectively located at the spherical center (S ₁ =R) and focus of the concave mirror). The traditional idea is that the aberration is finally transformed into the additional dispersion of the system, so it is believed that the Offner stretcher without aberration is better than the Martinez type stretcher with aberration. However, there are always various material dispersions in the amplification system. If the stretcher has no aberration, other additional methods are needed to compensate the material dispersion in the system. We think that if the aberration in the stretcher is properly reserved according to the material dispersion in the system (which can be estimated), the additional dispersion converted by this aberration is inversely signified by the material dispersion in the amplifier, then the image in the stretcher The aberration can make the system accommodate more material dispersion, therefore, the existence of proper aberration in the stretcher is beneficial to the dispersion compensation of the whole system, which is the starting point of this invention.

The present invention is realized through the following technical solutions: According to the relationship between the phase Φ of the stretcher and the position S ₁ of the grating, and the radius of curvature R of the spherical mirror:

$\mathrm{<span\; class="notranslate">\; \&Phi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;G</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}\mathrm{<span\; class="notranslate">\; the\; tan</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>$

Among them: p is the optical path in the stretcher calculated by the ray tracing method; d is the grating constant; γ is the incident angle _; Expressed as:

G ₀ =(2R-2S ₁ )cos(γ-θ ₀ ) and G=(S ₆ -S ₁ )cos(γ-θ ₀ ), A Miniaturized Femtosecond Laser Pulse Stretching Compensating for High Material Dispersion of Regenerative Amplifiers The device comprises a concave spherical mirror 1, a convex spherical mirror 2, a grating 3 and a plane mirror 4, and is characterized in that the grating 3 is arranged at a distance S ₁ from the concave spherical mirror, and the size of S ₁ is 0.2-0.3 meters; the convex spherical mirror and the grating are overlapped up and down. .

The technical point of the present invention is that for Offner-type stretchers, as S ₁ decreases, the aberration increases, so this design can compensate for more material dispersion of the amplifier than the non-aberration design, and it also causes the pulse of the stretcher Increased stretching capability. The reduction of R also increases the aberration, but reduces the pulse stretching capability of the stretcher, but as long as the reduction of the pulse stretching capability caused by the reduction of R and the pulse stretching capability caused by the reduction of S ₁ are guaranteed By increasing the phase balance, the original stretching amount can be kept unchanged, but the size of the entire stretcher will be greatly reduced, that is, a miniaturized femtosecond laser pulse stretcher suitable for high material dispersion compensation of regenerative amplifiers is formed.

The advantages of the present invention are that the Offner type stretcher can accommodate more material dispersion in the amplifier, and it is easy to collimate the optical path, the spatial dispersion is small, and the structure is especially compact, and its size is only that of the traditional Offner stretcher 1/3, which is 1/2 of the Martinez type stretcher.

Description of drawings

Fig. 1 is a schematic structural diagram of an existing Offner type stretcher.

Fig. 2 is a structural schematic diagram of the compact stretcher designed by the present invention.

In the figure: 1 is a concave spherical reflector, 2 is a convex spherical reflector, 3 is a grating, and 4 is a plane reflector;

Fig. 3 is the relationship curve between grating position and group delay when the regenerative amplifier is compensated for dispersion by using the stretcher designed in the present invention.

When S ₁ = 245mm in the figure, that is, the position of the grating satisfies that shown in Figure 2, the group delay curve is very flat in the range of 750-850nm, that is, the high material dispersion in the regenerative amplifier has been well compensated and can support narrower pulse, the size of the stretcher is only 1/3 of the existing device. And when S ₁ deviates from this position, the effect of dispersion compensation is poor (dotted line and dot-dash line)

Detailed ways

The embodiment of the present invention is described with the scheme of the Offner type pulse stretcher in the Ti:Sapphire laser amplifier. The miniaturized Offner-type pulse stretcher is composed of a concave spherical mirror 1, a convex spherical mirror 2, a grating 3 and a plane mirror 4, as shown in Figure 2. In order to realize miniaturization, the convex spherical mirror 2 and the grating 3 are overlapped (convex spherical mirror 2 is located above the grating 3); 2 and grating 3 transmission. The pulse stretching process of the miniaturized Offner-type pulse stretcher: the incident pulse first reaches the grating, is spread by the spectrum and diffracted to the concave spherical mirror 1; the concave spherical mirror 1 converges the spread spectrum to the convex spherical mirror 2, and then is reflected back Concave spherical mirror 1; the concave spherical mirror 1 collimates the light beam and reflects it to the grating; the light beam is diffracted by the grating to the plane mirror 4 along the incident direction; it is vertically reflected by the plane mirror 4, and the beam repeats the above process in the reverse direction, and the pulse is again After broadening, output along the incident direction. The distance _S1 between the grating of the miniaturized Offner-type pulse stretcher and the concave spherical mirror is between 0 and R (according to the size of the material dispersion in the system); on the premise of maintaining the required pulse stretching amount, select A spherical mirror with a small radius of curvature realizes a miniaturized femtosecond laser pulse stretcher suitable for high material dispersion compensation of a regenerative amplifier. The commercial specifications of the grating (1100/mm, 1200/mm, 1400/mm) and considering the pulse stretching rate, the grating of 1200/mm is generally selected. It is determined that the radius of curvature R of the concave spherical mirror 1 is 0.5 meters, the radius of curvature of the convex spherical mirror is 0.25 meters, and the two mirrors are placed concentrically. The distance between the grating surface and the concave mirror surface is adjustable, generally 0.2-0.3 meters.

Claims (1)

1. the miniaturization femto-second laser pulse stretcher of the high material dispersion of a compensational regeneration amplifier comprises concave spherical mirror (1), protruding spherical mirror (2), grating (3) and level crossing (4), it is characterized in that grating (3) is arranged on apart from concave spherical mirror apart from S ₁The place, S ₁Size be 0.2-0.3 rice; The overlapping placement up and down of protruding spherical mirror and grating.

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