KR20210118169A - Multi-stage optical parametric module and picosecond pulsed laser source with integrated module - Google Patents

Abstract

Multi-stage optical parametric (OP) module, and arranged along a single optical path to each of λp, λ3, and λ _f upstream wavelength pump, signal, and interact with the IR light beams from the multi intermediate and output optical parametric amplification (OPA ) is configured to have a stage. Each OPA stage is provided with a time delay compensation (TDC) assembly that alternates with the OPA stage along a single optical path. Each TDC assembly is configured to guide the IR, pump and signal beams along the optical path between the OPA stages while compensating for group velocity mismatch between the pump and signal beam and preventing propagation of the idler beam after each subsequent parametric interaction. do.

Description

Multi-stage optical parametric module and picosecond pulsed laser source with integrated module

The present disclosure relates to picosecond lasers. In particular, the present disclosure relates to use of high power quasi-continuous (QCW) picosecond lasers and OPA modules based on optical parametric modules configured to have a plurality of non-linear crystal based parametric amplifier (OPA) stages. .

Many scientific and industrial applications require high average power pulsed lasers with tunable central wavelengths, tunable spectral widths, and variable pulse durations in the visible frequency range. Although high-power single-mode (SM) lasers in the infrared frequency range have been developed and widely used in various industries, high-power blue lasers in general and specifically ultrafast high-power blue lasers with any desired output power anywhere from hundreds of watts to at least 1 kW. Not yet done in scope.

There are few practical technical approaches for generating blue laser light. One approach involves fabricating a blue diode laser based on gallium nitride (GaN). GaN-based diode lasers are not known for long lifetimes and have limited optical efficiency.

For many years, the most effective approaches to the development of ultrafast blue laser-based sources have been nonlinear transformations, i.e. Kerr-lens-mode-locked (KLM) Ti:sapphire lasers, Nd:YAG lasers, It was based on 3-fold and 4-fold increases in frequency of mode-locked lasers, including mode-locked EDFAs, and more recent nanosecond (ns) Yb-fiber lasers.

Another widely used approach to developing ultrafast blue laser sources is based on parametric non-linear optical devices. In particular, green-pumped OPAs, optical parametric oscillators (OPO) and OP generators (OPG) are attractive laser sources due to their wide tuning range and average power scalability. For example, a synchronously pumped optical parametric device is a viable ultrafast source of tunable coherent radiation that provides an average output over a wide spectral region.

The law of conservation of energy in parametric processes is:

(1)

(One)

SHS/SHI - Second harmonic generation of signal/idler:

(2)

(2)

SFS/SFI - Sum-Frequency generation (SFG) of signal/idler and IR laser wavelengths

(3)

(3)

1 illustrates an exemplary schematic diagram of a blue laser source based on a staged summing-frequency parametric amplifier as disclosed in USP 7,106,498. This schematic is reasonably representative of a conventional blue laser source and includes a splitter 1 that guides light fragments at fundamental and pump frequencies respectively along two different optical arms through multiple mirrors 9 . The outputs optically coupled together in a sum-frequency tunable generator (SFG) 14 include four optical signals 17, 18, 19, 20). The illustrated two-arm schematic with a splitter, combiner and multiple mirrors has a large footprint and complex configuration, which are major disadvantages of known blue lasers based on parametric amplification.

Among the various NLOs used in parametric processes, lithium triborate LiB3O5 (LBO) NL crystals have proven to be very good in damage protection and non-absorption, and as a result are suitable for high power parametric devices that would otherwise be easily damaged. Other borate NL crystals (β-barium borate, BaB2O4 or BBO and bismuth borate, BiB3O6 or BiBO) and periodically polarized NL crystals (PPLT, PPLN and PPKTP) can be equally effective, sometimes mostly with higher nonlinear coefficients ( deff) may outperform the LBO determination for parametric amplification. Unfortunately, when using BBO and BIBO, the desired minimum pulse peak output is relatively high due to the critical phase matching conditions used. The most common crystals with periodic polarity are susceptible to photorefractive or photochromic damage, limiting the scaling of the average power. However, various applications may only benefit from high average power blue light. Parametric transformation is not limited to blue light generation. Other wavelengths generated by the parametric process can be advantageously used in various industries.

Accordingly, it would be desirable to provide an adjustable microwave parametric module having a compact structure that does not feature optical splitters and combiners.

It is also desirable to provide a ps pulsed fiber laser source in combination with the disclosed parametric module.

In accordance with one aspect of the present disclosure, the multi-stage optical parametric (OP) module, upstream of the array and the interaction pump, signal and the IR light beam and in each of λp, λ ₃ and λ _f wavelengths along a single optical path, It is constructed with multiple intermediate and output optical parametric amplification (OPA) stages. Each OPA stage is provided with a time delay compensation (TDC) assembly that alternates with the OPA stage along a single optical path. Each TDC assembly is configured to guide the IR, pump and signal beams along the optical path between the OPA stages while compensating for group velocity mismatch between the pump and signal beam and preventing propagation of the idler beam after each subsequent parametric interaction. do.

According to a further aspect of the present disclosure, the optical pump is configured with a linearly polarized (LP) ps fiber laser source that pumps the optical parametric module. Advantageously, but not exclusively, the disclosed source may be used to simultaneously output red, green and blue light. The ps laser source is configured with a mode-locked ps fiber laser that uses chirped pulse amplification (CPA) technology to produce an output at a fundamental wavelength in the 1 μm spectral range. By properly selecting the desired fundamental wavelength, the source can simultaneously output red and blue light with an average pulse power exceeding 100 W. For example, the fundamental wavelength may be selected from the group consisting of 1030, 1048, 1060 and 1071 nm.

Each of the above aspects is characterized by a plethora of features that can be structurally coupled to one another as detailed in the specific description and claims below. The features of each aspect may be combined in a manner readily discernible to one of ordinary skill in the laser art.

These and other aspects and features of the present disclosure will become more readily apparent with reference to the following drawings, in which:
1 is an optical schematic diagram of a blue laser according to the known prior art;
2 is a schematic diagram of a fiber light source of the present invention;
Fig. 3a is a schematic diagram of a red light generating OPA module incorporated in the fiber laser source of the present invention of Fig. 2;
Fig. 3B is an example of a parametric blue light generating module combined with the red light generating module of Fig. 3A;
Fig. 3C is another example of a blue light generating module combined with the red light generating module of Fig. 3A;
3D is another example of an OPA module;
3e is a further example of an OPA module of the present invention;
4A is a detailed optical schematic diagram of a blue laser of the present invention according to one specific example;
4B is a detailed optical schematic diagram of a blue laser of the present invention according to another example;
5 illustrates the blue-red wavelength relationship of the disclosed RG light source;
6 is an optical schematic diagram of the disclosed ps fiber laser based pump module;
7 is a schematic diagram of an example of a pulse replicator module in accordance with aspects of the present invention;
8 is a schematic diagram of another example of a pulse replicator module in accordance with aspects of the present invention.

Reference will now be made in detail to the disclosed system. Wherever possible, the same or similar reference numbers are used in the drawings and description to refer to the same or similar parts or steps. The drawings are in simplified form and are not at all to scale. For convenience and clarity only, "connect," "join," "combines," and similar terms having their inflected morphemes do not necessarily denote direct and immediate connection, but also include coupling through an intermediary element or device.

Figure 2 schematically illustrates a light source 10 of the invention comprising several modules optically coupled to each other. The fiber laser source module 12 operates to generate a train of ps IR pulses propagating along the optical path, for example, at a fundamental wavelength λf selected from 1030, 1048, 1060 or 1071 nm. The IR beam interacts with the NLO of the pump 14 to convert a portion of the IR light into pump light at the pump wavelength λp = λf/2 to produce SH. The pump 14 may also be packaged in a pump module 16 that includes a fiber laser source 12 and outputs the pump and the remaining IR light at λp and λf wavelengths, respectively. Parametric NLO module 18 is configured to process the output received from pump module 16 and output red, green, and blue light at respective signal, pump and blue wavelengths. As disclosed below, various structural examples illustrate the concepts of the present invention. Common to all disclosed examples is an optical schematic of an NLO module 18 comprising several OPA stages positioned along a single optical path, as better illustrated in the following figures.

3A-3C illustrate the operating principle and structure of the NLO 16 of FIG. 2 . In particular, FIG. 3A illustrates four OPA stages each comprising an LBO crystal. The upstream OPA1 is configured to generate a signal beam, i.e., red light in the wavelength range of 777 - 854 nm, which is guided along the optical path through a subsequent intermediate OPA2-OPA3 stage where it is progressively amplified. The schematic diagram shown requires including at least three or more upstream and intermediate LBO OPA stages to provide sufficient amplification of the light component propagated and produced therein because the peak power of the fiber laser source 12 is limited by a few MW. there is A laser source not shown here but disclosed below outputs ps IR pulses coupled to a second harmonic generator (SHG) (not shown here), after which the IR light is filtered and quantum noise The green light generated at the pump wavelength λp with Consequently, the latter outputs the green pump light beam, the generated red signal beam, and the idler beam at respective signal and idler wavelengths λ ₃ , λ _{4 .}

Ultrafast OPA requires time-delay compensation (TDC) for the group velocity mismatch between the pump and signal pulse beam at the output of the LBO crystal. Thus, prior to further parametric amplification of the red signal beam in LBO OPA stage 2, the propagating green/pump and red signal beams are incident on _{TDC 1 positioned in-line with all OPA stages between adjacent LBO OPA stages.} In summary, the OPA module 18 is configured to have a plurality of OPA stages and TDCs that alternate with each other along the optical path.

A TDC is an optical system of components that may include a chirped mirror, a dichroic mirror (discard idler), and a birefringent window made of various materials and placed at various temperatures. Consequently, spectral tuning can only be achieved by changing the temperature of the LBO, using, for example, a combination of chirped mirrors and material dispersion.

The operation disclosed above is repeated whenever the red signal is amplified in the four sequentially positioned stages OPA1-OPA4 shown, while the idlers created in each OPA stage are discarded by the designated TDC1-TDC3 before the subsequent OPA stage. As one of ordinary skill in the art knows, no meaningful parametric interaction will occur if the idler is coupled to the subsequent OPA stage. At the output of the schematic diagram shown, the source light strikes a spectral filter, such as a dichroic mirror, which is transparent to the amplified red signal and reflects the green pump light to a designated output.

FIG. 3B , illustrating an OPA block having the configuration of FIG. 3A , shows an example of an output blue light generating OPA stage of module 18 of the present invention of FIG. 2 . In particular, _{the red signal beam at signal wavelength λ 3} is amplified according to the schematic diagram of FIG. 3a and is further coupled to the output LBO SHG to generate a second harmonic, ie a blue light beam. An additional dichroic mirror transmits the red signal beam, but reflects the resulting blue light beam.

3C shows another example of an output blue light generating OPA stage that utilizes both polarizations of output blue and red light. In particular, the output OPA stage is configured with two SHGs spaced apart from each other along the optical path and adjacent to a fourth TDC4 comprising a double half-wave plate. At the output of module 18 , the cross polarized blue light and the remaining red light are incident on a subsequent dichroic mirror that separates these lights at the output of the source 10 of FIG. 2 . It is noted that the schematic diagram of the NLO module 18 of FIGS. 3B and 3C provides separate outputs for each of the green, red, and blue light advantageously used in the RGB engine as disclosed below.

3D and 3E illustrate _{a slightly different configuration of an NLO module 18 using IR light at the fundamental wavelength λ f} , some of which remain after the upstream SHG configured to generate a green light beam at the pump wavelength. (not shown here). In particular, FIG. 3D illustrates a multi-stage NLO module 18 configured similar to that of each of FIGS. 3A-3C . The IR light is incident on the OPA block configured identically to Figure 3a and propagates through all OPA stages unaffected by the parametric operation. Thus, as shown in this figure, the output of the OPA block includes an IR light beam, a signal red light beam and a pump green light beam, all of which impinge on an output upstream dichroic mirror that is transparent to both red and IR light. But it reflects green light. The IR and red light beams are combined into an SFG stage that produces blue light as a result of mixing the combined IR and red light. An output downstream dichroic mirror spaced downstream from the SFG along the optical path reflects blue light and transmits the remainder of the IR and red light beams. Accordingly, the source 10 includes three output ports traversed by each of the red, green, and blue light beams.

Fig. 3e advantageously offers the possibility of using orthogonal polarization directions of the red, blue and IR light beams, as in Fig. 3c. This is realized by the combination of spaced upstream and downstream outputs LBO SFG1 and LBO SFG2 and TDC4. The latter contains a triple half-wave plate with another mirror and is located between SFG1 and SFG2. The upstream output SFG mixes the IR and red light beams resulting in a blue light beam output. All three lights are incident on the triple half-wave plate which shifts the polarization direction of the linearly polarized light. The downstream SFG provides the summation frequency generation of blue light with a polarization direction orthogonal to the polarization of the blue light at the input of this SFG. At the output of the downstream SFG, cross-polarized light is incident on the output dichroic mirror to reflect the blue light beam and transmit the red/IR light beam.

Referring to FIGS. 3A-3E previously described, it can be readily seen that the disclosed schematic features alternating OPAs and TDCs positioned in-line and together defining a single optical path through the illustrated overall arrangement. The experimental phase of the previously disclosed structure has yielded very promising results. For example, for a 50% conversion efficiency, the ultrafast OPA of FIGS. 3A-3C can be pumped by 50 - 500 nJ pulse energies easily achieved by a regular fiber laser. Using low absorption and high damage threshold LBO bulk NLOs instead of commonly used periodically polarized materials, the schematic diagram of the previously disclosed light source 10 (FIG. It is plausible that it is possible to produce a blue light pulse output greater than 1 kW with a spectral linewidth.

4A illustrates an exemplary detailed optical schematic diagram of a light source 10 producing a source blue output in the 443 - 467 nm wavelength range. The illustrated schematic is configured to provide a single linear angular light path. However, a person skilled in the art of lasers can easily reconstruct the schematic diagram shown to have an inline architecture similar to that shown in FIGS. 3A-3E and to be configured identically to the schematic diagrams of FIGS.

Specifically, the laser module 12 generates ps pulses of IR light at a 1030 nm fundamental wavelength λf and a green pump signal at a pump wavelength λp = 515 nm. During the second harmonic generation, a portion of the IR light is passed to the pump signal at SHG 14 in FIG. 2 . A train of ps pulses at the fundamental and pump wavelengths is a focal lens that trains each pulse to the central region of the first NLO 26 functioning as both the OPG/A parametric devices constituting the upstream stage of the NLO module 18 . Enter (L2). The first nonlinear crystal 26 interacts with the green pump beam to produce a red light signal beam and an idler beam at the third and fourth wavelengths λ3 and λ4, respectively. The combination of the fundamental wavelengths remaining after some have interacted with the upstream SHG (not shown) propagates freely between the output of OPG 26 and the input of SFS 46, and with NLO 26 of the upstream OPA stage After the interaction between the pump signal beams, a fragment of the pump light beam at the λp wavelength and the red light signal beam generated at the λ3 wavelength are incident on the first dichroic mirror 28 . The dichroic concave mirror 28 is transparent to the idler, but reflects the pump and signal light beams in opposite and non-parallel directions so that the reflected light is incident on the same NLO 26 acting as an OPA. . Thus, the dichroic mirror 28 is part of the TDC assembly that compensates for the group velocity mismatch between the reflected pump and the red light beam. As the reflected light propagates through the NLO 26 of the upstream OPA stage in the opposite direction, a similar process as for the NLO 26 in the other direction is repeated.

As the reflected light interacts with the first NLO 26, the red signal beam at the signal wavelength λ3 is further amplified. The idler beam at wavelength λ4 is regenerated and propagated coaxially with the further attenuated green pump beam and the amplified red light beam. Upon impacting the dichroic planar mirror 30 , light beams of all wavelengths except the newly created idler propagating through the mirror 30 are reflected towards at least one intermediate OPA stage of the module 18 .

The reflected light beam is further incident on and reflected from a planar mirror 32 which directs the light towards a concave mirror 34 that reflects in one direction through a second non-linear crystal of the intermediate OPA stage. The interaction between the second NLO 36 and the pump signal further amplifies the red signal at λ3 which is then incident on the dichroic mirror 38 along with the remaining pump signal, the red signal and the idler. is transmitted through this mirror. The reflected light propagates through the second NLO 36 in the opposite direction, repeating a process similar to that in the upstream OPA stage. As a result, the amplified red signal, the third fragment of the pump, the idler and IR at each of λ3, λp, λ4 and λf impinges on the flat mirror 40 and directs all light except the idler towards the downstream stage.

Like the previous OPA stage, the downstream stage is configured to have a flat mirror 42 and a curved mirror 44 that sequentially guide light received in one direction through an SFG (denoted SHS) containing an LBO NLO 46 . do. The latter mixes the previously amplified red light signal at wavelength λ3 with the remaining IR light at wavelength λf to produce a source signal output at ^{wavelength λsso =(1/λf + l/λ3) −1 .} Thus, the output ps blue light is transmitted through the flat mirror 52 at wavelengths in the 443 - 467 nm wavelength range.

As shown, the remaining red and IR light at each pump λ3 and signal λ _{f wavelength can be further used.} This light is reflected from the curved mirror 48 in the opposite direction through the NLO 46 to again generate blue light incident on the flat mirror 50 and is further reflected towards the flat mirror 54 of the output stage. Half-wave plate 56 is in optical communication with mirror 54 and is configured to alter the polarization of the blue light to be orthogonal to the polarization of the blue light transmitted through mirror 48 . Downstream of the half-wave plate 56, a thin film polarizer (TFP) 58 couples the blue light output at the desired 443 or 467 nm center wavelength. In general, the output OPA stage can have a variety of parametric devices alone or in combination with devices that produce the desired output wavelength. Therefore, any type of parametric generation including the transform type including summation frequency, difference frequency, summation frequency, difference frequency and second harmonic generation suitably constitutes an output stage that can be realized by a person skilled in the art. can be used by

As previously described, all OPA stages can each be configured to provide a single pass LBO NLO. With this change, the schematic diagram of FIG. 4A can be reconfigured to provide an inline architecture identical to that shown in FIGS. 3A-3E but with twice as many LBO NLOs.

4B illustrates another example of an OPA module 18 of the present invention of a source 10 that outputs a 343 nm blue light beam. The source used in FIG. 4B includes a ps UV fiber laser source (not shown) operating at a 343 nm pump wavelength. Constructed generally similar to the schematic diagram of FIG. 4A , module 18 has a downstream OPA stage provided with an optical parametric amplifier instead of the SFG NLO of the previously disclosed module with a pump beam of 515 nm wavelength.

Various types of NLO determinations may be used within the context of this disclosure. The decision may or may not be critically phase matched for any existing spatial walkoff that can be compensated for by the WOC plate. Thus, crystal types such as BBO, BIBO, KTP, KTA, periodically polarized LiNbO 3 (PPLN), periodically polarized LiTaO 3 (PPLT), etc. can be implemented in the schematic diagrams of FIGS. 2 and 3 . However, the only crystal capable of providing more than 100 W in output power is LBO (and possibly BIBO) as it has the lowest bulk absorption and highest damage threshold than all other alternative NLO crystals. The NLO may or may not be a non-critical phase matched crystal. If any spatial walk-off exists, it can be compensated as known to those skilled in the art. Each NLO crystal is individually thermally controlled to provide the best phase matching conditions.

The NLO module 18 disclosed above is particularly advantageous when used in an RGB engine in a visual display where all three primary colors must be generated from one laser source. The efficiency of an RGB engine is based on the following key considerations: First, the primary red, green and blue colors must be selected so that the human eye can detect more than 90% of the color gamut. Second, the speckle phenomenon that causes image distortion should be minimized and preferably eliminated. In addition, the RGB light source should be characterized by high wall plug efficiency and high luminous efficacy of the converted visible light at the minimum output power of the fiber pump as disclosed in this application. However, the display industry is not the only one benefiting from the disclosed source 10 of FIG. 2 . For example, the same parametric module 18 shown in FIGS. 3A-3E uses an IR light beam as a pump beam and uses BIBO crystals instead of LBO crystals to provide an output in the 1.7 - 2.5 μm wavelength range. It has been proven. Structurally, the output OPA stage may be configured with two SHGs, and the remaining OPA stage may be configured with a parametric amplifier similar to FIGS. 4A and 4B .

Returning to FIG. 2 , the pump module 16 includes a ytterbium (Yb) doped mode-locked ps fiber laser 12 . Most industrial Yb fiber lasers operate at about 1030 nm or 1064 nm (emission) fundamental wavelength λf. The selection of any of these wavelengths determines the configuration of the NLO module 18 as described below.

FIG. 5 is a blue color based on Equations 1, 2 and 3 with a 515 nm pump wavelength generated by SHG 14 interacting with an IR signal from Yb fiber laser 12 at 1030 nm fundamental wavelength ( FIG. 2 ). -Illustrating the red wavelength relationship. Curve 120 is determined using a combination of two second harmonic generators (SHG and SHGi) that interact with light of each pump wavelength. Alternatively, curve 120 may be modeled using a combination of summing frequency generators SFG and SFGi. According to another alternative, curve 120 is modeled using a combination of SFG and SHG parametric devices. This curve 120 indicates that the desired red and blue wavelengths can be obtained by using two SHG devices or two SFG devices. If the blue light wavelength has been changed to, for example, a 445 nm wavelength but a 610 nm idler wavelength is still needed, the combination of SFG stages corresponds to curve 122 . Curve 124 corresponding to the combination of SHG and SFG stages indicates that this combination cannot be used for efficient RGB 10 if a 610 nm idler wavelength is required. Combinations of various parametric devices can result in a desired wavelength. Ultimately determining one or another combination of parametric mechanisms that can be readily obtained using the structural flexibility of the NLO module 18 of FIGS. 3A-3E and 4A-4B to adapt to any desired wavelength is is the efficiency of the light source 10 .

Table 1 provides the parametric operation and necessary data used by the high efficiency RGB source 10 at the 1030 nm fundamental wavelength to generate blue and signal (red) outputs at the 478 nm and 610 nm wavelengths, respectively. As can be seen, the RGB source 10 is configured with an NLO 18 comprising SHG at a wavelength of 1220 nm to produce the desired source idler output at a wavelength of 610 nm. However, to generate the source output signal at the 478 nm wavelength, the SHG mechanism does not work effectively. However, using an SFG device that interacts with a signal at 892 nm, it is possible to efficiently operate an RGB source 10 at a 478 nm source signal output. Additionally, this table provides linewidths for the source signal, pump, and source idler outputs, with 3 nm, 4 nm, and 5 nm linewidths, respectively, to help prevent speckle. The efficiency of converting IR light of the fundamental wavelength to the respective red, green and blue signals at the minimum power of the laser source of the module 12 is considered to be very high, between 8% and 20%, while the output red and blue signal average power is also extraordinary for a medium 2D cinema at 158 W, 106 W and 114 W respectively. It is believed that there is no comparable conversion efficiency and power for this type of projector in the respective red and especially blue spectral regions.

The relationship of the different wavelengths shown in Table 1 is based on the pump module 16 of FIG. 2 generating pump light at a wavelength of 515 nm. Other pump wavelengths may be used with the parametric NLO module 18, which is obviously based on the law of conservation of energy of optical parametric processes. Table 2 illustrates the signal red and blue wavelengths generated from OPA/OPO pumped by green light at 532 nm wavelength, which is the SH of IR light at 1064 nm wavelength. Table 2 provides the data and parametric mechanisms that make RGB light sources from 1064 nm sources most efficient for 2D cinemas.

6 illustrates a fiber laser pump module 12 based on a ps fiber source 100 with a chirped pulse amplification (CPA) architecture combined with pulse replication. Source 100 may have a variety of configurations, including full fiber or YAG based structures. Preferably, the source features a MOPA configuration comprising a master oscillator outputting a train of ps pulses and a fiber or other type of amplifier or booster 150 . The source 100 also has a pulse stretcher 130 , a pulse replicator module 140 , an isolator 160 positioned both between the seed and the booster, and a pulse compressor 170 followed by a fiber booster 150 . is composed The input laser pulses 112 are stretched in time using a pulse stretcher 130 , amplified in an amplification stage comprising a booster 150 and optionally a preamplifier 154 , and compressed using a pulse compressor 170 . is released Prior to amplification, the stretched pulse 132 is replicated using a pulse replicator module 140 .

Pulse stretcher 130 is configured to stretch a pulse duration of an input train of pulses 112 to produce a train of stretched pulses 132 with reduced peak output. According to some embodiments, the pulse stretcher 130 stretches the pulses of the initial pulse train 112 to a pulse duration on the order of a few nanoseconds, which may be 10 ns in some cases. The repetition rate of the stretched laser pulse 132 may be increased by a pulse replicator module 140 , which duplicates the optical waveform of the stretched laser pulse 132 in a timely manner to produce a modified pulse train 148 . create The time plot of the train of stretched laser pulses 132 output by pulse stretcher 130 has a pulse period of t and a pulse repetition rate of 1/t. According to some embodiments, the pulse replicator 140 may be used to replicate the stretched laser pulses such that t is reduced to the extent that the laser energy of the modified pulse train 148 appears continuously. The near continuous wave characterization of the modified pulse train 148 is a function of both the stretching performed by the pulse stretcher 130 and the replication performed by the pulse replicating module 140 . Examples of systems using such laser light are described in more detail below. The pulse replicator 140 may be configured to increase the repetition rate of the stretched laser pulse 132 to several tens of MHz and multi-GHz levels. Pulse stretcher 130 and/or pulse replicator module 140 may be configured to generate modified pulses 148 having a desired peak-to-average power ratio. An example is described below.

The pulse duplicator module 140 is a full fiber device comprising at least two fiber optic couplers comprising an input fusion fiber coupler and an output fiber coupler and at least one fiber optic delay line disposed between the input and output fusion fiber couplers. All fiber optic couplers are polarization-maintaining. The fiber optic coupler may also be configured as a single mode non polarization-maintaining (PM) fused fiber coupler. Components of pulse stretcher 130 and pulse replicator module 140 may be configured to output pulses at a custom (high) repetition rate. The pulse compressor 170 compresses the pulse width of the chirped amplified pulse 153 . Non-limiting examples of pulse compressors include lattice compressors such as CVBG and Treacy compressors, as well as Martinez compressors and prism compressors.

The amplified and compressed laser pulses 174 output from the pulse compressor 170 may be characterized as ultrashort pulse laser light having a high repetition rate and high average power. Specific uses of this power include the generation of high average power UV laser radiation and are described below.

5 is a schematic diagram of a first example of a pulse replicator module 440 . According to this configuration, the input fusion optical fiber coupler 442 is configured as an optical fiber splitter. One of the two fibers exiting the coupling region of the output fiber coupler 443 forms an output 436 comprising a modified pulse train 148 . Optical beamsplitter 442 has an input 434, in which case input 434 is coupled to optical pulse stretcher 130 (FIG. 4) and output 436 of output coupler 443 is a fiber coupled to or otherwise coupled to the output amplifier 150 . The pulse replicator module 440 also includes at least one fiber optic coupler 444 disposed between the input coupler 442 and the output coupler 443 .

For one of the outputs of the input splitter 442, a delay τ is added using a single mode fiber of an appropriate length (i.e., fiber delay line 445), so that one leg or output segment 445 of the pair is has a different (longer) optical path length than the other legs 446 . This produces two pulses separated by τ in both output fibers 445 ₁ and 446 _{1 of splitter 442 .} A delay of 2τ enters one of these paths to produce two sets of four pulses when these two outputs are coupled in coupler 444 . This process can be repeated, doubling the differential delay between the two paths until the desired number of replicas are obtained. The two paths are then combined using a combiner 443 . The length of the delay τ may be chosen to be slightly longer than the length of the laser pulses to avoid pulse overlap and interference.

The pulse replicator 440 includes a plurality of stages 449 each including a fiber delay line 445 such that each successive stage introduces a time delay in the elongated laser pulse 132 . For the example shown in FIG. 5 , pulse replicator 440 includes four stages 449 ₁ , 449 ₂ , 449 ₃ , 449 ₄ , where at each stage the signal output is divided by a fixed time delay and are reunited Since the number of replicas is doubled in each stage 449 (ie, a 50:50 coupler), the two outputs 445 ₄ and 446 ₄ propagating to the combiner 443 each ^{contain 2 x} replicas, where x is the number of stages used (x = 4 in this example). Accordingly, the pulse replicator 440 is configured as a multi-stage passive pulse replicator where each successive stage introduces a fixed time delay to the elongated laser pulse 132 . The time delay may increase or decrease by a predetermined amount in each successive stage.

The outputs of the last stages 445 ₄ and 446 ₄ of replicator 440 are combined in combiner 443 to produce a train of time delayed replica pulses as modified pulse train 148 at output 436 . As can be seen in FIG. 6 , _{each of the eight replicate pulses of the fiber legs 445 4} and 446 ₄ are combined in a combiner 443 to produce 16 pulses. These 16 pulses are configured as pulse bursts, so the modified pulse train 148 will contain a sequence of pulse bursts each containing 16 pulses. The length of the delay lines 445 _{1 -} 445 ₄ represents the burst repetition rate (ie, the time interval between bursts).

As will be appreciated, components of pulse stretcher 130 and pulse replicator module 140 may be configured to output pulses at a custom repetition rate. The repetition rate can be chosen such that the peak output is low enough to avoid undesirable damage, but high enough for efficient frequency conversion. The fiber coupler and fiber delay lines of the pulse replicator module may be used to generate various pulse shapes, and FIG. 8 is a schematic diagram of another example of a pulse replicator module 540 . According to some embodiments, the pulse duplicator module may include a sequence of submodules, each of which may be configured separately. For example, the pulse replicator module 540 shown in FIG. 5 uses the output of the pulse replicator module 440 of FIG. 7 as an input, but the replicator module 540 is also a submodule on its own or with other configurations. It should be understood that it can be used with

In a manner similar to the replicator module 440 of FIG. 6 , the pulse replicator module 540 also includes an input fusion fiber coupler 542 and an output fiber coupler 543 . Between the input coupler 542 and the output coupler 543 are intermediate fiber couplers 544, 547a, and 547b. Instead of a delay line from each stage 549 being directed to an adjacent (downstream) stage, at least one delay line bypasses one or more downstream stages as shown in the configuration of FIG. 6 . According to this example, the delay line 545 ₄ is directed from the intermediate coupler 544 to the output coupler 543 at the output of the first stage 549 _{1 , whereby the second and third stages 549 2} and 549 ₃ ) and form the delay line of the fourth stage 549 _{4 .} As such, the time delay increments introduced in each successive stage are not all equal to each other. As shown in FIG. 5 , this configuration has an initial 16 pulse burst with a total duration (envelope) of 9 ns _{through 4 stages 549 1} -549 4 160 pulses with an envelope of 90 ns bursts, where each pulse duration is 0.45 ns and the pulses are separated by 0.56 ns. Table 1 below outlines each stage.

The examples of pulse replicators shown in FIGS. 7 and 8 are not intended to be limiting and other configurations are also within the scope of the present disclosure.

Thus, while various aspects of at least one example have been described, it should be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. For example, examples disclosed herein may also be used in other contexts. Such changes, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the examples described herein. Accordingly, the description and drawings described above are merely examples.

Claims (22)

A multi-stage optical parametric (OP) module comprising:
An upstream optical parametric amplification (OPA) stage configured to receive a linearly polarized pump beam at a pump wavelength λp _{and generate a signal and idler beam at wavelengths λ 3} and λ ₄ , respectively - the pump, a fragment of the signal and idler beam is a single light propagated along the path -;
a plurality of intermediate OPA stages optically coupled to one another along the optical path and each subsequent OPA stage receiving progressively weaker fragments of the pump beam and an amplified signal beam from the preceding OPA stage;
a plurality of times configured to alternate with the OPA stage along the path, compensate for group velocity mismatch between the pump and signal beam, and guide the pump and signal beam along the optical path while preventing propagation of idlers after each subsequent parametric interaction delay compensation (TDC) assembly; and
An OP module comprising an output OPA stage configured to receive a fragment of the pump beam and the amplified signal beam and to generate an output beam at a desired output wavelength λo different from _{a wavelength λ 3 of the signal beam.} 2. The signal beam of claim 1, wherein the signal beam is progressively amplified in at least two or more intermediate OPA stages each configured to have an optical parametric amplifier, the optical parametric amplifier comprising LBO, BBO, BiBO, KTP, KTA, periodically polarized; OP module comprising nonlinear crystals each selected from LiNbO3 (PPLN), or periodically polarized LiTaO3 (PPLT). 3. The method of claim 2, wherein the output OPA stage for generating the output beam comprises at least one or more summed frequency generation (SFG) parametric devices, at least one or more second harmonic generation (SHG) parametric devices, or a combination of SFG and SHG parametric devices. , wherein the parametric devices each include a non-linear determination. The OP module of claim 1 , wherein the output OPA stage is configured with a half-wave plate that modifies the polarization of the output beam, and a combiner configured to combine the two polarizations of the output beam such that the output beam is cross-polarized. The OP module of claim 1 , wherein the output OPA stage is configured with two spaced apart upstream and downstream SFG devices and a half-wave plate between the SFG devices. The OP module of claim 1 , wherein the TDC assembly is each configured to have a chirped mirror, a dichroic mirror, or a birefringent window or a combination of a mirror and a birefringent window. The method of claim 1 , wherein the pump wavelength λp is in the green light range centered at 515 nm wavelength and the output wavelength λo is in the blue light 443 - 467 nm wavelength range, or the pump wavelength λp is in the IR light range centered at 1030 nm wavelength and the output wavelength λo is in the range of 1700 - 2500 nm, the OP module. The OP module of claim 1 , wherein the upstream, intermediate and output OPA stages and TDC assemblies are all in-line along a straight single light or are positioned along an inclined single light path. The OP module of claim 1 , further comprising at least one output wavelength filter that provides output separation for the pump, signal, and output beam. The method of claim 1 , wherein the OPA stages are spaced apart from each other along a single inclined light path,
The upstream and intermediate OPA stages each include an optical parametric amplifier (OPA) with the pump and signal beams traversed in one and opposite non-parallel directions along a single angular path light;
The output OPA stage comprises at least one summation frequency generation (SFG) parametric device, at least one second harmonic generation (SHG) parametric device, or a combination of SFG and SHG parametric devices, the OPA stage having two outputs at the output wavelength λo. A pump that crosses the output OPA stage in one and opposite directions to produce a beam, a fragment of the signal and output beams, and cross polarization combined by shifting the linear polarization of one of the output beams and further combining the output beam with a different polarization an OP module comprising a polarization assembly configured to provide an output beam. A picosecond (ps) single mode (SM) pulsed laser source comprising:
a ps fiber laser based optical pump that operates to produce a linearly polarized pulsed pump beam at a pump wavelength λp along a single optical path;
Receive the pump beam downstream of the optical pump, i.e.:
an upstream optical parametric amplification (OPA) stage configured to receive a linearly polarized pump beam at a pump wavelength λp _{and generate a signal and an idler beam at respective wavelengths λ 3} and λ _{4 propagating along a single optical path;}
a plurality of intermediate OPA stages optically coupled to one another along the optical path and each subsequent OPA stage receiving progressively weaker fragments of the pump beam and an amplified signal beam from the preceding OPA stage;
a plurality of times configured to alternate with the OPA stage along the path, compensate for group velocity mismatch between the pump and signal beam, and guide the pump and signal beam along the optical path while preventing propagation of idlers after each subsequent parametric interaction a wavelength conversion parametric module, configured with a delay compensation (TDC) assembly; and
A picosecond single mode pulsed laser source comprising an output OPA stage configured to receive a fragment of the pump beam and the amplified signal beam and generate an output beam at a desired output wavelength λo. 12. The pico of claim 11, wherein the signal beam is increasingly amplified in at least two or more intermediate OPA stages, each configured to have an optical parametric amplifier, each comprising LBO or a nonlinear crystal selected from BBO or BiBO. Ultra-single-mode pulsed laser source. 12. The method of claim 11, wherein the output OPA stage for generating the output beam comprises at least one or more summed frequency generation (SFG) parametric devices, at least one or more second harmonic generation (SHG) parametric devices, or a combination of SFG and SHG parametric devices. wherein the parametric devices each comprise a nonlinear crystal. 12. The picosecond single mode pulsed laser source of claim 11, wherein the output OPA stage is configured to have a half-wave plate that modifies the polarization of the output beam, and a combiner configured to combine the two polarizations of the output beam such that the output beam is cross-polarized. . 12. The ps SM pulsed laser source of claim 11, wherein the output OPA stage is configured with two spaced apart upstream and downstream SFG devices and a half-wave plate between the SFG devices. 12. The picosecond single mode pulsed laser source of claim 11, wherein the TDC assembly is each configured to have a chirped mirror, a dichroic mirror or a birefringent window or a combination of a mirror and a birefringent window. 12. The method of claim 11, wherein the pump wavelength λp is in the green light range centered at 515 nm wavelength and the output wavelength λo is in the blue light 443-467 nm wavelength range, or the pump wavelength λp is in the IR light range centered at 1030 nm wavelength and the output wavelength λo is in the range of 1700 - 2500 nm, and the blue light ps pulses at the output wavelength λo have an average power of up to 1000 W, respectively, and a spectral linewidth range of 1.5 to 3 nm, a picosecond single mode pulsed laser. sauce. 12. The picosecond single mode pulsed laser source of claim 11, wherein the upstream, intermediate and output OPA stages and the TDC assembly are in-line with each other or along an oblique single light path light. 12. The picosecond single mode pulsed laser source of claim 11, further comprising at least one output wavelength filter that provides output separation for the pump, signal, and output beam. The method of claim 11 , wherein the fiber laser based optical pump comprises:
a Yb mode-locked fiber laser configured to operate in a pulsed or burst region providing an input train of ps pulses at a fundamental wavelength λf;
an optical pulse stretcher configured to stretch a pulse duration to produce a train of stretched pulses;
a pulse duplicator module optically coupled to the optical pulse stretcher and configured to split each pulse into a plurality of replicas;
a fiber output amplifier optically coupled to the pulse replicator module and configured to amplify each replica;
a pulse compressor optically coupled to the fiber output amplifier and configured to temporally compress the amplified replicas into respective ps pulses at a fundamental wavelength; and
A picosecond single mode pulsed laser source comprising a second harmonic generator (SHG) that outputs a pump output beam at a pump wavelength λp. 21. The method of claim 20, wherein the pulse replicator module comprises one or a plurality of time delay stages, each delay stage disposed between an input beamsplitter, an output fusion fiber coupler, and therebetween to provide a time delay between adjacent replicas. A picosecond single mode pulsed laser source comprising a fiber optic delay line, wherein the time delay is increased or decreased by a predetermined amount in each successive stage, the predetermined amount being the same for all stages or different in at least one stage. 21. The picosecond of claim 20, wherein the optical pump has a fiber master oscillator and output amplifier (MOPA) architecture, the master oscillator is a Yb mode-locked fiber laser with a ring resonator, and the output amplifier is a fiber amplifier or Yb:YAG. Single mode pulsed laser source.

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