35a is mode-locked with a SAM, giving a FWHM spectral bandwidth of 6 to 8 nm and an average power of 1 to 1.5 mW, depending on the property of SAM and the Er-fiber. 10% of the output 35a is split by a fiber coupler and sent to PD0 for the oscillator power monitoring. This OSC power monitor provides a feedback to the electronic board controlling the applied voltage to EVOA1 391 for a constant output power control of the OSC 35. The remaining 90% will be split in 50/50 and sent to the 1 fÊm generation stage 320 and the 1560 nm CPA stage (the second amplifier) 360, respectively.

The function of the stage 320 is to generate 1 fÊm wavelength narrowband first source laser light 33 from the 1560 nm base laser 35a as the first laser source. The purpose is to obtain the exactly the same repetition rate for both 1 fÊm arm and 1.5 fÊm arm. In this stage 360, the power amplification is done with an EDFA (Er02) built within this stage 360 and the average output power from the amplifier is ˜18 mW. 1% of the power is coupled out and sent to PD1 right at the output of the amplifier for power monitoring. The signal from PD1 becomes the feedback to the board controlling EVOA2 392 so the output power from this EDFA can remain constant. The EDFA output pulse will be compressed directly by a piece of fiber providing negative dispersion. At the splice spot to the HNLF 325, the FWHM pulse duration is compressed down to ˜60 fs, corresponding to a peak power of ˜25 KW. An optical pulse with this peak power sent into a short piece of HNLF makes the wavelength extend from 1560 nm and eventually covers a range from 1 fÊm to 1.7 fÊm. This is the so-called SC generation process. That is, with this peak power, the pulse propagates in the HNLF 325 with strong nonlinear effects and the spectrum can be broadened from 1560 nm to both short and long wavelengths, eventually forming a supercontinuum spectrum spanning from 1 μm to 1.7-1.8 μm. This 1 fÊm part is our target which will be harvested for the next stage of amplification 330.

The 1032 nm CPA stage 330 includes the preamplification, pulse stretch and the final amplification processes. The 50% pump split branch not connected to any EVOA in the distributor 390 is split to 50/50 again here by another fiber coupler (FL16). One arm goes to the preamplifier 340 in this 1032 nm CPA stage 330, and the other goes to the preamplifier 370 of 1560 nm CPA stage 360, which will be introduced later. The generated 1 fÊm will be sent into the port #1 of a 1 fÊm CIR 333. From the port #1 to the port #2 of this CIR 333, only the 1 fÊm part will be selected from the SC spectrum due to the component property. At the port #2, an Yb-fiber (Yb01), a CFBG 335, and a 1030/980 WDM/Tap hybrid component 336 are spliced in sequence. The selected 1 fÊm seed meets the Yb-fiber first and gets amplified. Then the CFBG 335 reflects ˜40% power within a wavelength range from 1018 nm to 1053 nm. Wavelengths outside of this range will directly transmit the CFBG 335 and come out from the WDM 336. The output of WDM 336 is used as the monitor of spectrum (to tap2) and power (to PD2) after this preamplifier 340. The reflected part will pass through the Yb-fiber (Yb01) again and have the second amplification before going back into the port #2. The pre-amplified 1 fÊm pulse going into the port #2 comes out from the port #3 of the CIR 333. At this point, the 1 fÊm pulse has been stretched and ready to be amplified in the final amplifier 350.

LD1 396 is an individual laser diode providing the pump power up to 850 mW for 1032 nm final amplifier 350. First the seed from the CIR port #3 will spliced with an isolator/WDM hybrid component 337. This component protects the previous stages from the damages due to the reflected light and the residual pump. An Yb-fiber (Yb02) and a WDM 338 are then spliced in sequence to complete the construction of the 1032 nm CPA stage 330. The final output (first light source) 95 provides optical pulses at 12 MHz with a FWHM pulse duration of ˜66 ps. The spectral FWHM bandwidth is ˜14 nm and the average output power directly from the FC/APC connector connected to a collimator should be in a range from 450 mW to 520 mW. A 1% Tap is coupled to PD3 and tap3 for the power and spectrum monitoring, respectively. PD3 also provides the feedback to form a control loop for the constant output from the 1032 nm CPA stage 330.

The 1560 nm CPA stage 360 also includes the preamplification, pulse stretch and the final amplification processes. The concept is identical to the 1032 nm CPA stage 330 but only a slightly difference in the components due to the operation in different wavelength region. The pump source of the preamplifier 370 is the other half of the split pump from the distributor 390. The seed of 1560 nm beam (second source pulses) 34 is the other half of the split from the 80% of the OSC output 35a. The same idea of the 1032 nm CPA stage 330 is applied for the 1560 nm CPA stage 360, but the 1560 nm CPA stage 360 uses 1560 nm CIR 361 port #1 to bring the seed to the preamplification and the pulse stretching processes by using CFBG 363 and WDM 364 components working at 1560 nm. LD2 397 is another individual laser diode providing the pump power up to 850 mW for 1560 nm final amplifier 380. From the port #3 of CIR 361, the pre-amplified seed is sent to the Er-fiber (Er04) and a Tap/Isolator/WDM hybrid component 365 to complete the 1560 nm CPA stage 360.

The final output provides optical pulses at 12 MHz as the 1560 nm output 96. The FWHM pulse duration is ˜35 ps and the FWHM spectral bandwidth is ˜7 nm. The average output power is in a range of 130 mW to 180 mW. A 1% Tap is coupled to PD4 and tap4 for the power and spectrum monitoring, respectively. PD4 also provides the feedback to form a control loop for the constant output from the 1560 nm CPA stage 360.

FIG. 4 depicts one of the embodiments of the laser module 30 of this invention. This laser module 30 is a full fiber laser module and includes the oscillator 35 for supplying the base laser 35a with mode-locked to be split to the first source laser light 33 and the second source laser light 34, the 1 fÊm laser generation stage (first laser source) 36 for generating the narrowband first source laser light 33 from the base laser 35a, and a plurality of routes (optical fiber routes, optical fiber sections) 310. The plurality of routes 310 includes: (i) a first route 301 for splitting the first source light pulses 33 for generating broadband first light pulses (Stokes light pulses) 51 and narrowband second light pulses (pump light pulses) 52; (ii) a second route 302 for amplifying and broadening a range of wavelengths with a first train 81 that includes a first amplifier 81b, a first hollow-core photonic crystal fiber (HCPCF) 81a, and highly non-liner photonic crystal fiber (HNLPCF) 85 spliced directly (without free space) to supply the broadband first light pulses (the Stokes light pulses) 51; (iii) a third route 303 for amplifying with a second train 82 that includes a second amplifier 82b and a second HCPCF 82a spliced directly (without free space) to supply the narrowband second light pulses (the pump light pulses) 52: (iv) a fourth route 304 for multiplexing the Stokes light pulses 51 and the pump light pulses 52 and outputting the Stokes light pulses 51 and the pump light pulses 52 overlapping in time as an irradiation beam 31 to irradiate the target 5; and (v) a fifth route 305 for generating a narrowband third light pulses (the probe light pulses) 53 with a third train 83 that includes a third amplifier 83b, a third HCPCF 83a and a SHG 23s spliced directly (without free space) to supply the probe light pulses 53. The first route 301, the second route 302, the third route 303 and the fourth route 304 configure the Stokes-pump pulse generation stage 37 for generating the Stokes light pulses 51 and the pump light pulses 52 from the first source laser light 33. The fifth route 305 configures the probe pulse generation stage 38 for generating the probe light pulses 53 from the second source laser light 34.

The oscillator 35 may have the same or common configurations with those described with reference to FIG. 3. The 1 fÊm laser generation stage 36 may include the generator 320, or the generator 320 and the 1 fÊm laser preamplifier 340 described above. The first route 301 may include a 50/50 coupler 309 for separating the first source laser light 33 to the second route 302 and the third route 303 and a narrow band filter 301a for conditioning the input for the narrowband pump light pulses 52. The range of wavelengths the first source laser light 33 is centered at 1030 nm.

The first train (first arm, first line, first series of optical fibers) 81 in the second route 302 may include a stretching fiber 81d, a preamplifier 81c, the amplifier 81b, the HCPCF 81a and the HNLPCF 85 connected without free space. The preamplifier 81c and the amplifier 81b may respectively have the same or common configurations with the preamplifier 340 and the amplifier 350 described above. For the stretching, instead of the stretching fiber 82d, the configurations using the CFBG described in the 1032 nm CPA stage 330 can be applied.

The HCPCF 81a replaces the free-space compressor applied in the optical module 90 described above and delivers the compressed high peak power pulses at the end of the HCPCF 81a. The HCPCF 81a can be directly spliced to the HNLPCF 85 to use it as the supercontinuum PCF (SCPCF) for generating the broadband Stokes light pulses 51. The documents suggest that the HCPCF 81a can be used as an outstanding fiber beam delivery or extremely efficient nonlinear compressor (For example, Martin Maurel, Matthieu Chafer, Benoit Debord, Foued Amrani, Benoit Beaudou, et al. Scalable hollow fiber pulse compressor for NIR and UV lasers. SPIE Photonic West 219 February 2019, San Francisco, United States. Paper 10899. hal-02329692).

By using the first train 81 which includes the first amplifier 81b, the first HCPCF 81a, and the HNLPCF 85 directly spliced, the all-fiber Stokes generation from the first source laser light 33 having the range of wavelengths centered at 1030 nm can be provided and, before the final collimating, alignment-free Stokes light pulses 51 can be supplied. In the second route 302, by splicing (connecting) directly (without free space) two different types of photonic crystal fibers (PCFs), i.e., HCPCF 81a and HNLPCF 85 with the amplifier 81b, the compression function provided by the HCPCF 81a and the supercontinuum (SC) generation function provided by the HNLPCF 85 can be integrated into a single series of fibers (the first train) 81 with the amplifier 81b. Hence, the system 1 and the optical module 10, which include the laser module 30, can be made compact by omitting one or more free-space grating compressors and other free-space optical elements.

In addition, by using the all-fiber (full-fiber) Stokes generation system (the second route) 302, the loss in the free-space propagation can be reduced, so the power level of the Stokes light pulses 51 can be easily increased or the energy consumption in the laser module 30 can be reduced. For using the HCPCF 81a as the compressor, it is expected that HCPCF 81a of 5 to 12 m in length, and even more suitably 7 to 9 m, will be required for the broadband Stokes light pulse generation.

The second train (second arm, second line, second series of optical fibers) 82 in the third route 303 may include a stretching fiber 82d, a preamplifier 82c, the amplifier 82b and the HCPCF 82a connected without free space. The preamplifier 82c and the amplifier 82b may respectively have the same or common configurations with the preamplifier 340 and the amplifier 350 described above. For the stretching, instead of the stretching fiber 82d, the configurations using the CFBG described in the 1032 nm CPA stage 330 can be applied.

By using the second train 82 which includes the second amplifier 82b and the second HCPCF 82a directly spliced, the all-fiber pump generation from the first source laser light 33 having the range of wavelengths centered at 1030 nm can be provided and, before the final collimating, alignment-free pump light pulses 52 can be supplied. In the third route 303, by splicing (connecting) HCPCF 82a directly (without free space) with the amplifier 82b, the integrated single series of fibers (the second train) 82 is provided. Hence, the system 1 and the optical module 10, which include the laser module 30, can be made compact by omitting one or more free-space grating compressors and other free-space optical elements.

In addition, by using the all-fiber (full-fiber) pump generation system (the third route) 303, the loss in the free-space propagation can be reduced, so the power level of the pump light pulses 52 can be easily increased or the energy consumption in the laser module 30 can be reduced. For using the HCPCF 82a as the compressor, it is expected that HCPCF 82a of 10 to 20 m in length, and even more suitably 12 to 15 m, will be required for the narrowband pump light pulse generation.

The fourth route 304 may include a chirp rate conditioner 308 for varying at least one of a chirp rate of the Stokes light pulses (first light pulses) 51 supplied by the first route 302 and a chirp rate of the pump light pulses (second light pulses) 52 supplied by the third route 303 to make them substantially equal. This fourth route 304 includes the chirp rate conditioner 308 for controlling the chirp rate of the Stokes light pulses 51. The chirp rate conditioner 308 may include a CIR 308a and a CFBG 308b connected to the CIR 308a. The output from the second route 302 is injected into the CFBG 308a via the CIR 308a