Non-regenerative optical ultrashortpulse amplifier

Abstract

Non-regenerative optical amplifier has a first optical amplifying medium and at least one second optical amplifying medium. The non-regenerative optical amplifier may be an ultrashort pulse amplifier. The material properties of the first amplifying medium differ at least partially from the material properties of the second amplifying medium. The emission spectra of the amplifying media overlap partially, and the amplifying media are solid-state bulk crystals.

Claims

1. Non-regenerative optical ultrashort pulse amplifier, comprising: a) a first optical gain medium; b) a second optical gain medium; c) the material properties of the first optical gain medium differ at least partially from the material properties of the second optical gain medium; d) the emission spectra of the first and second optical gain media partially overlap, the emission spectra of the first and second optical gain media are selected to overlap in such a way that a gain spectrum results which is spectrally expanded as compared to the individual emission spectra of the respective first and second optical gain medium; e) the first and second optical gain media are formed by solid-state bulk crystals; f) at least one of the first and second optical gain media contains a host crystal which is doped with a dopant; and g) the dopant is Nd or Yb.

2. Ultrashort pulse amplifier according to claim 1, wherein: a) the gain media have an emission effective cross section (emission efficiency) of >110.sup.19/cm.sup.2.

3. Ultrashort pulse amplifier according to claim 2, wherein: a) the solid-state bulk crystals each have a length of greater than 1000 m along the optical axis.

4. Ultrashort pulse amplifier according to claim 1, wherein: a) the host crystal contains one of YVO.sub.4, GdVO.sub.4, LuVO.sub.4, Ylf, and YAG.

5. Ultrashort pulse amplifier according to claim 1, wherein: a) an excitation light source is designed for mode-selective longitudinal excitation of the first and second optical gain media.

6. Ultrashort pulse amplifier according to claim 5, wherein: a) the excitation light source for exciting the first and second gain media has an excitation wavelength for excitation at 800-1000 nm.

7. Ultrashort pulse amplifier according to claim 1, wherein: a) the output signal of the amplifier is a pulse signal having a pulse duration of 0.5 ps to 50 ns, in particular 0.5 ps to 10 ps.

8. Ultrashort pulse amplifier according to claim 1, wherein: a) the first and second optical gain media are situated in direct succession in the irradiation direction of an excitation light source.

9. Ultrashort pulse amplifier according to claim 1, wherein: a) for influencing the absorption curve in a targeted manner, the first and second optical gain media which are situated in direct succession in the irradiation direction of the excitation light source have different absorption properties.

10. Ultrashort pulse amplifier according to claim 1, wherein: a) the first and second optical gain media include at least one laser crystal which is tilted relative to the optical axis of the amplifier.

11. Ultrashort pulse amplifier according to claim 1, wherein: a) the input signal of the amplifier originates from seed source such as a fiber oscillator or solid-state oscillator which is one of mode-coupled and pulsed in some other way, or a semiconductor laser.

12. Ultrashort pulse amplifier according to claim 1, wherein: a) the solid-state bulk crystals each have a length of greater than 1000 m along the optical axis.

13. Ultrashort pulse amplifier according to claim 1, wherein: a) at least one of the first and second optical gain media contains a host crystal which is doped with a dopant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The figures show the following:

(2) FIG. 1a shows a first embodiment of an amplifier according to the invention in a highly schematic, block diagram-like manner;

(3) FIG. 1b shows an embodiment of a further amplifier stage, which may be situated downstream from the second amplifier stage of the first embodiment of FIG. 1a;

(4) FIG. 2 shows a diagram for illustrating the individual emission spectra of the gain media used in the amplifier according to FIG. 1a;

(5) FIG. 3 shows a diagram for illustrating the resulting emission spectrum of the amplifier according to FIG. 1a;

(6) FIG. 4 shows, in the same manner as FIG. 1a, a second embodiment of an amplifier according to the invention;

(7) FIG. 5 shows a diagram for illustrating the spatial dependency of the absorption of the excitation light in the embodiment according to FIG. 4;

(8) FIG. 6 shows, in the same manner as FIG. 1a, a third embodiment of an amplifier according to the invention; and

(9) FIG. 7 shows a diagram for illustrating the spatial dependency of the temperature along the crystal axis during operation of the amplifier according to FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

(10) Identical or corresponding components are provided with the same reference numerals in the figures of the drawing.

(11) FIG. 1a illustrates a first embodiment of a non-regenerative optical amplifier according to the invention. An excitation light source by means of which excitation light is irradiated into the amplifier is denoted by reference numeral 1. The excitation light source may be configured as a fiber-coupled light source or as a free space light source. In the present embodiment, a lens system which is composed of two lenses 2, 3 and used for focusing the excitation light beam is situated downstream from the excitation light source 1. The lens system is situated downstream from a first mirror 4 which is highly reflective for the laser wavelength of a first optical gain medium (laser medium), but highly transmissive for the wavelength of the excitation light. An input beam to be amplified, denoted by reference numeral 6 in FIG. 1a, is coupled in via a second mirror 8. The first optical gain medium 5, which in the present embodiment is formed by a doped host crystal, namely, Nd:YVO.sub.4, is situated between the mirrors 4, 8. The above-described arrangement forms a first amplifier stage 10 of the amplifier. The output beam of the first amplifier stage 10 is deflected via the mirror 4 to a second amplifier stage 12 which in its basic design corresponds to the first amplifier stage 10. However, unlike the first amplifier stage 10, the second amplifier stage 12 has a second gain medium (second laser medium 5), which in the present embodiment is formed by a doped host crystal, namely, Nd:GdVO.sub.4. The output beam of the amplifier is denoted by reference numeral 7 in FIG. 1a.

(12) According to the invention, the gain media 5, 5 are formed as solid-state bulk crystals whose length along the optical axis in the present embodiment is greater than 1000 m.

(13) Thus, due to the use of different laser crystals, the material properties of the first laser medium 5 differ from the material properties of the second laser medium 5, the emission spectra of the laser media 5, 5 partially overlapping according to the invention.

(14) If necessary or desired, depending on the individual requirements, even further amplifier stages may be situated downstream from the second amplifier stage 12, as indicated by reference numeral 14 in FIG. 1b.

(15) Due to the use of the different laser media 5, 5 having partially overlapping emission spectra, the amplifier illustrated in FIG. 1a makes possible generation of a new, expanded gain spectrum, and thus, amplification of laser pulses in the range of approximately 0.5 ps to 10 ps.

(16) FIG. 2 shows a diagram for illustrating the emission spectra of the laser media 5, 5.

(17) FIG. 3 illustrates the emission spectrum, denoted by reference numeral 16, which results when the laser media 5, 5 are used. One possible input spectrum to be amplified, having a half-width value of approximately 2 nm, is denoted by reference numeral 18 in FIG. 3. With this spectral width of the emission spectrum, amplification of pulses in the range of below 1 ps, for example, is possible.

(18) FIG. 4 illustrates a second embodiment of an amplifier according the invention which differs from the embodiment according to FIG. 1a in that the different laser media within the amplifier stage are situated between the mirrors 4, 8. Strictly by way of example, FIG. 4 illustrates three laser media 5, 5, 5 situated in direct succession, i.e., without mirrors or other beamforming or beam-deflecting apparatuses situated in between.

(19) The third laser medium 5 is illustrated strictly by way of example and representative of the fact that, depending on the particular requirements, any arbitrary number of laser media may be used. The following discussion considers the properties which result from combining the first laser medium 5 with the second laser medium 5.

(20) In the illustrated embodiment, the material properties of the laser media 5, 5 are selected for influencing the absorption curve along the crystal axis in a targeted manner.

(21) FIG. 5 illustrates the absorption curve along the crystal axis, the absorption curve for the individual crystals being denoted by reference numerals 20, 20, and the absorption curve which results from combining the laser media or laser crystals 5, 5 being denoted by reference numeral 22. In the illustrated embodiment, the laser crystals 5, 5 are Nd:YVO.sub.4, laser crystal 5 being 0.2 at %-doped, and the other laser crystal 5 being 0.5 at %-doped.

(22) As is apparent from FIG. 5, the absorption curve and thus the longitudinal distribution of the pump power may be influenced in this way. In addition, due to the improved absorption, the length of the laser crystals or laser media 5, 5 may be shortened, which allows better spatial overlap between laser modes and pump mode. This has a beneficial effect on the overall efficiency of the amplifier system.

(23) FIG. 6 illustrates a third embodiment of an amplifier according to the invention in which the laser crystals 5, 5 are each tilted with respect to the optical axis. Due to the tilting of the laser crystals 5, 5 with respect to the optical axis, undesirable effects such as parasitic lasers or amplified spontaneous emission (ASE) are avoided. Corresponding tilting of the gain media with respect to the optical axis may also be used in the preceding embodiments.

(24) FIG. 7 shows the temperature curve along the crystal axis which results during operation of the amplifier. The temperature curve which results when an individual laser crystal is used is denoted by reference numeral 24. In contrast, the temperature curve which results when two laser crystals are used, as illustrated in FIG. 4, is denoted by reference numeral 26. It is apparent from FIG. 7 that the maximum temperature which occurs in the laser crystals may be greatly reduced by using two laser crystals 5, 5. The reduction in temperature is advantageous for temperature-dependent effects, such as thermally induced stresses which may result in destruction of a laser crystal, and thermo-optical effects such as the thermal lens.

(25) The invention thus opens up new possibilities for the design of non-regenerative optical amplifiers.

(26) While this invention has been described as having a preferred design, it is understood that it is capable of further modifications, and uses and/or adaptations of the invention and following in general the principle of the invention and including such departures from the present disclosure as come within the known or customary practice in the art to which the invention pertains, and as may be applied to the central features hereinbefore set forth, and fall within the scope of the invention.