A laser crystallization apparatus comprising: a light source unit (LS) configured to irradiate a laser beam (B); and an optical unit (OP) to which the laser beam (B) is incident, in use, in an incident direction, wherein the optical unit (OP) includes a first portion (Pa) and a second portion (Pb) bonded to each other to form a bonded surface (Sab), and wherein a first width (Wa) of the first portion (Pa) and a second width (Wb) of the second portion (Pb) are the same as each other at the bonded surface (Sab) based on a direction parallel to the incident direction of the laser beam (B); wherein the optical unit (OP) comprises a plurality of sub-optical units (O1, O2, O3, O4, O5), characterised in that each of the plurality of sub-optical units (O1, O2, O3, O4, O5) includes a first portion (Pa) and a second portion (Pb) bonded to each other to form a bonded surface (Sab), and wherein the plurality of sub-optical units (O1, O2, O3, O4, O5) are sequentially arranged in the direction parallel to the incident direction of the laser beam (B); and wherein the plurality of sub-optical units (O1, O2, O3, O4, O5) include a first sub-optical unit (O1) and a second sub-optical unit (O2), and a length (L01) of a first portion (O1a) of the first sub-optical unit (O1) is different from a length (L02) of a first portion (O2a) of the second sub-optical unit (O2); and wherein the bonded surface (Sab1) of the first sub-optical unit (O1) and the bonded surface (Sab2) of the second sub-optical unit (O2) are disposed parallel to each other and offset from each other in the direction parallel to the incident direction of the laser beam (B). a light source unit (LS) configured to irradiate a laser beam (B); and an optical unit (OP) to which the laser beam (B) is incident, in use, in an incident direction, wherein the optical unit (OP) includes a first portion (Pa) and a second portion (Pb) bonded to each other to form a bonded surface (Sab), and wherein a first width (Wa) of the first portion (Pa) and a second width (Wb) of the second portion (Pb) are the same as each other at the bonded surface (Sab) based on a direction parallel to the incident direction of the laser beam (B); wherein the optical unit (OP) comprises a plurality of sub-optical units (O1, O2, O3, O4, O5), characterised in that each of the plurality of sub-optical units (O1, O2, O3, O4, O5) includes a first portion (Pa) and a second portion (Pb) bonded to each other to form a bonded surface (Sab), and wherein the plurality of sub-optical units (O1, O2, O3, O4, O5) are sequentially arranged in the direction parallel to the incident direction of the laser beam (B); and wherein the plurality of sub-optical units (O1, O2, O3, O4, O5) include a first sub-optical unit (O1) and a second sub-optical unit (O2), and a length (L01) of a first portion (O1a) of the first sub-optical unit (O1) is different from a length (L02) of a first portion (O2a) of the second sub-optical unit (O2); and wherein the bonded surface (Sab1) of the first sub-optical unit (O1) and the bonded surface (Sab2) of the second sub-optical unit (O2) are disposed parallel to each other and offset from each other in the direction parallel to the incident direction of the laser beam (B). <EOS>