CN105006735A - Double-crystal multi-pass type femtosecond laser amplification system - Google Patents

Abstract

The present invention discloses a double-crystal multi-pass type femtosecond laser amplification system which comprises a bi-directional pumping device, a double-crystal amplification gain medium formed by first and second crystal gain mediums of different substrates, and a multi-pass signal amplification cavity formed by first and second plane reflection mirrors of a dichroic mirror. A forward pumping source device convex lens and a reverse pumping source device convex lens are arranged between a forward pumping device semiconductor laser pump source and a reverse pumping device semiconductor laser pump. The distance between the convex lens and a pumping device is the focal length of the respective convex lens. Two crystal gain mediums are as close as possible in the condition of no contact damage, and the crystal centers of the two crystals are at the centers of the respective pumping light. The first and second plane reflection mirrors are respectively arranged between the crystal gain mediums and the pumping device convex lenses. According to the system, the width of a gain spectrum can be expanded appropriately, the gain narrowing effect to light spectrum by the gain spectrum is reduced, and thus the output of a narrow pulse and high energy is obtained.

Description

Double crystal multi-pass femtosecond laser amplification system

technical field

The invention relates to a multipass femtosecond laser amplifier based on doped crystals.

Background technique

The femtosecond laser amplifier is the key to improving the femtosecond laser power and energy. There are two commonly used amplifier schemes, one is a fiber amplifier and the other is a bulk crystal amplifier. Due to the thin and long waveguide structure of the fiber, the fiber amplifier has good heat dissipation characteristics and is suitable for high average power femtosecond laser amplification. However, the waveguide structure greatly increases its nonlinear coefficient, so that the femtosecond laser accumulates too much nonlinear phase shift during the amplification process, which leads to the deterioration of pulse quality and limits the output pulse energy of the amplifier. For bulk crystal amplifiers, when amplifying femtosecond laser pulses, due to the large focus spot and short action distance in the crystal, the accumulated nonlinear response is much smaller than that of fiber amplifiers, and higher single pulse energy can be obtained. At present, most femtosecond lasers with single pulse energy greater than 100 μJ use bulk crystal amplifiers.

For femtosecond laser amplifiers, another important parameter is the gain spectrum of the gain medium, which directly determines the narrowest pulse width of the amplified pulse. According to the Fourier transform relationship, a wider spectrum supports a narrower time-domain width. However, during the amplification process, the gain narrowing effect will limit the output spectrum of the femtosecond laser amplified. The larger the gain factor of the amplifier, the more obvious the gain narrowing, and the narrower the amplified spectrum. For signal light with a wide spectrum, due to the gain narrowing effect at high gain, the output spectral width is often smaller than the incident spectral width, and the transformation limit time domain width of the amplified pulse is wider than the incident pulse. Therefore, the block crystal amplifier is limited to obtain narrow pulses.

In order to overcome this deficiency and further expand the gain spectral width of bulk crystal amplifiers, many new broadband crystals have been proposed, but due to the complex manufacturing process of the new crystals, the quality is relatively poor, and more importantly, the gain bandwidth of the new crystals is also limited. Cannot grow without limit. Therefore, there is an urgent need to study a solution to the problem of limited pulse width caused by gain bandwidth, and at the same time use common bulk crystal gain media to obtain high-energy, narrow-pulse femtosecond laser amplification output.

Contents of the invention

In view of the prior art, using a single Yb-doped crystal as the gain medium of the amplification stage, the gain bandwidth is limited, and the gain narrowing phenomenon occurs when the gain is high, which limits the time domain width of the amplified pulse. The present invention provides a double crystal The multi-pass femtosecond laser amplification system can properly expand the width of the gain spectrum and reduce the gain narrowing effect of the gain spectrum on the spectrum, so as to obtain narrow pulse and high-energy output.

In order to solve the above technical problems, the present invention proposes a dual-crystal multi-pass femtosecond laser amplification system, comprising: a forward pumping device semiconductor laser pump source, a forward pumping device convex lens, a reverse pumping device semiconductor laser A two-way pumping device composed of a pump source and a reverse pumping device convex lens; a double crystal amplification gain medium composed of a first crystal gain medium and a second crystal gain medium of different substrates; a first crystal gain medium that is a dichromatic mirror A multi-pass signal amplification cavity composed of a plane reflector and a second plane reflector; wherein: the semiconductor laser pump source of the forward pumping device and the semiconductor laser pump source of the reverse pumping device are respectively arranged at both ends of the overall structure The convex lens of the forward pumping device and the convex lens of the reverse pumping device are arranged between the semiconductor laser pump source of the forward pumping device and the semiconductor laser pump source of the reverse pumping device; the convex lens of the forward pumping device The distance between the semiconductor laser pumping source of the forward pumping device and the convex lens of the reverse pumping device and the semiconductor laser pumping source of the reverse pumping device are respectively the focal lengths of the respective convex lenses themselves; the first The first crystal gain medium and the second crystal gain medium are as close as possible without contact damage, and the crystal centers of the first crystal gain medium and the second crystal gain medium are respectively located at the centers of the respective pumping lights ; The first plane mirror is arranged between the first crystal gain medium and the convex lens of the forward pumping device, and the second plane mirror is arranged between the second crystal gain medium and the reverse pumping device Between the device convex lenses; the distance between the first plane reflector and the second plane reflector is adjusted according to the required number of reflections and the incident angle.

Compared with prior art, the beneficial effect of the present invention is:

It can properly expand the width of the gain spectrum and reduce the gain narrowing effect of the gain spectrum on the spectrum, so as to obtain narrow pulse and high energy output.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the dual-crystal multi-pass femtosecond laser amplification system of the present invention.

In the picture:

1-Forward pumping device semiconductor laser pump source 2-Forward pumping device convex lens

3-The first flat mirror 4-The first crystal gain medium

5-Second crystal gain medium 6-Second plane mirror

7-Reverse pumping device Convex lens 8-Reverse pumping device Semiconductor laser pump source

Detailed ways

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the described specific embodiments are only for explaining the present invention, and are not intended to limit the present invention.

As shown in Figure 1, a dual-crystal multi-pass femtosecond laser amplification system of the present invention includes the following devices:

A bidirectional pumping device consisting of a semiconductor laser pump source 1 for a forward pumping device, a convex lens 2 for a forward pumping device, a semiconductor laser pump source 8 for a reverse pumping device, and a convex lens 7 for a reverse pumping device;

A double-crystal amplification gain medium composed of a first crystal gain medium 4 and a second crystal gain medium 5 of different substrates;

A multi-pass signal amplifying cavity composed of a first plane mirror 3 and a second plane mirror 6, both of which are dichroic mirrors.

The positional relationship between the above components is:

The semiconductor laser pump source 1 of the forward pumping device and the semiconductor laser pump source 8 of the reverse pumping device are respectively arranged at both ends of the overall structure;

The convex lens 2 of the forward pumping device and the convex lens 7 of the reverse pumping device are arranged between the semiconductor laser pump source 1 of the forward pump device and the semiconductor laser pump source 8 of the reverse pump device; The distance between the convex lens 2 of the pumping device and the semiconductor laser pump source 1 of the forward pumping device and the distance between the convex lens 7 of the reverse pumping device and the semiconductor laser pump source 8 of the reverse pumping device are respectively the convex lens itself the focal length;

The first crystal gain medium 4 and the second crystal gain medium 5 are as close as possible without contact damage, and the crystal centers of the first crystal gain medium 4 and the second crystal gain medium 5 are respectively located at the center of the respective pump light;

The first plane mirror 3 is arranged between the first crystal gain medium 4 and the convex lens 2 of the forward pump device, and the second plane mirror 6 is arranged between the second crystal gain medium 5 and Between the convex lens 7 of the reverse pumping device; the distance between the first plane reflector 3 and the second plane reflector 6 is adjusted according to the required number of reflections and the incident angle, while ensuring that the incident pulse and the outgoing pulse are not Blocked by a dichroic mirror.

The double crystal amplification gain medium in the present invention is made up of different substrates, the first crystal gain medium 4 and the second crystal gain medium 5 of the same doped particles, the two crystals should have close but inconsistent emission cross-sections, and the two crystals are superimposed The rear gain spectrum is wider than the gain spectrum when the two crystals work separately. Commonly used doped crystals usually have different central wavelengths and bandwidths, and the bandwidth is relatively narrow. The multiplexing of the two crystals is used in the amplification stage, which can effectively utilize the complementarity of their gain bandwidths, thereby expanding the gain bandwidth, and finally realizing The signal light is amplified over the entire spectral range. At the same time, professionals in the industry can also use crystals of different thicknesses, different doping concentrations, different doping ions, and different substrates to obtain a relatively flat gain spectrum through calculation and design, so as to achieve a more uniform gain curve in crystal amplification, as much as possible Effect of lower gain narrowing on signal light.

The bidirectional pumping device in the present invention realizes the pumping of the two crystals before and after it respectively from two directions, and the two crystals can be adjusted separately by using the bidirectional pumping device, so as to realize the effect of optimizing the parameters of the amplifier . The bidirectional pumping device consists of two identical pumping devices, each of which includes a pumping source and a convex lens, that is, the semiconductor laser pump source 1 of the forward pumping device and the convex lens 2 of the forward pumping device constitute the forward pumping device , the semiconductor laser pump source 8 of the reverse pump device and the convex lens 7 of the reverse pump device constitute the reverse pump device. The pump source emits divergent pump light, which is collimated and shaped by a convex lens, and the light beam is evenly hit on the first crystal. Similarly, the reverse pump device hits the backward pump light on the second crystal. The magnification efficiency is maximized by optimizing the focal length parameters of the convex lens and the relative positions of the convex lens, the pump source and the crystal.

The multi-pass signal amplifying cavity in the present invention is composed of two plane mirrors (the first plane mirror 3 and the second plane mirror 6), both of which are dichroic mirrors, that is, reflecting laser light and transmitting pump light. The incident pulse is incident into the multi-pass signal square cavity at a small angle (non-zero degree), and passes through the double crystal amplifying medium once, the pulse is reflected on the plane mirror, and passes through the double crystal again, so that the incident pulse passes through the two mirrors The structures in which the incident pulses are multiple-passed and amplified are realized by sequentially reflecting and passing through the twin crystals multiple times. By adjusting the incident angle of the incident pulse and the plane mirror and the distance between the two plane mirrors, the number of pulse reflections in the cavity can be controlled, thereby indirectly controlling the gain system of the amplifier and optimizing the amplification parameters. Using a multi-pass signal amplification cavity can make the signal light pass through the double crystal structure multiple times to gradually amplify. Using the similar but different gain spectra of the two crystals, the influence of gain narrowing caused by single crystal amplification can be avoided as much as possible.

Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only illustrative, rather than restrictive. Under the enlightenment of the present invention, many modifications can be made without departing from the gist of the present invention, and these all belong to the protection of the present invention.

Claims (2)

1. a bicrystal multi-way Femtosecond Laser Amplification System, is characterized in that, comprising:

The two directional pump device be made up of forward pumping device semiconductor laser for pumping source (1), forward pumping device convex lens (2), backward pumping device semiconductor laser for pumping source (8) and backward pumping device convex lens (7);

The bicrystal gain amplifier medium be made up of first piece of crystal gain medium (4) and second piece of crystal gain medium (5) of different substrates;

The multi-way signal enlarged cavity be made up of the first plane mirror (3) and the second plane mirror (6) respectively for dichroic mirror;

Wherein:

Described forward pumping device semiconductor laser for pumping source (1) and backward pumping device semiconductor laser for pumping source (8) are arranged in integrally-built two ends;

Described forward pumping device convex lens (2) and backward pumping device convex lens (7) are arranged between described forward pumping device semiconductor laser for pumping source (1) and backward pumping device semiconductor laser for pumping source (8); Described forward pumping device convex lens (2) and forward pumping device semiconductor laser for pumping source (1) spacing and distance between described backward pumping device convex lens (7) and backward pumping device semiconductor laser for pumping source (8) be the focal length of respective convex lens self respectively;

Described first piece of crystal gain medium (4) and second piece of crystal gain medium (5) close as far as possible when not contact failure, and the germ nucleus of described first piece of crystal gain medium (4) and second piece of crystal gain medium (5) lays respectively at the center of respective pump light;

Described first plane mirror (3) is arranged between described first piece of crystal gain medium (4) and forward pumping device convex lens (2), and described second plane mirror (6) is arranged between described second piece of crystal gain medium (5) and backward pumping device convex lens (7); Spacing between described first plane mirror (3) and described second plane mirror (6) order of reflection as required and incident angle adjust.

2. bicrystal multi-way Femtosecond Laser Amplification System according to claim 1, it is characterized in that, the position of described first plane mirror (3) is finely tuned to exit end, the position of described second plane mirror (6) is finely tuned slightly toward incidence end, thus ensures that incident pulse and outgoing pulse do not stop by dichroic mirror.